REstricted Versus Liberal Positive End-Expiratory Pressure in Patients Without Acute Respiratory Distress Syndrome
Phase: NA
Conditions: Ventilator-free Days
Sponsor: Academisch Medisch Centrum - Universiteit van Amsterdam (AMC-UvA)

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Research protocol 
 
REstricted versus Liberal positive end–expiratory 
pressure in patients without Acute respiratory 
distress syndrome (RELAx) – a multicenter 
randomized controlled trial 
 
A.G. Algera1, L. Pisani1, C.A.J.M. de Borgie2, T.G. Cherpanath1, R.M. Determann4, 
A.M. Dondorp1,5, D.A. Dongelmans1, J. Horn1,3, N.P. Juffermans1,2, D.M.P. van 
Meenen1, M.P. Merkus3, P.R. Tuinman6,7, M. Gama de Abreu8, P. Pelosi9, A. Serpa 
Neto1,10, A.P.J. Vlaar1,2, M.J. Schultz1,2,5 and F. Paulus1 for the RELAx investigators 
of the PROVE network* 
 
Academic Medical Center, Amsterdam, The Netherlands: 
1Department of Intensive Care 
2Clinical Research Unit 
3Laboratory of Experimental Intensive Care & Anesthesiology (L·E·I·C·A) 
 
Westfriesgasthuis, Hoorn, The Netherlands: 
4Department of Intensive Care 
 
Madihol University, Bangkok, Thailand: 
5Madihol Oxford Research Unit (MORU) 
 
VU Medical Center, Amsterdam, The Netherlands: 
6Department of Intensive Care 
7REVIVE Research VU Medical Center 
 
University Hospital Carl Gustav Carus, Dresden, Germany: 
8Department of Anesthesiology and Intensive Care 
 
IRCCS San Martino IST, University of Genoa, Liguria, Italy: 
9Department of Surgical Sciences and Integrated Diagnostics 
 
Hospital Israelita Albert Einstein, São Paulo, Brazil: 
10Department of Intensive Care Medicine 
 
 
*PROVE Network, Protective Ventilation Network, www.provenet.eu 
 
 
Correspondence: 
Prof. Marcus J. Schultz, MD PhD 
Principal Investigator 
Department of Intensive Care, C3–423 
Meibergdreef 9 
1105 AZ Amsterdam 
Email address: m.j.schultz@amc.uva.nl 

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Title: REstricted versus Liberal positive end–expiratory pressure in patients 
without Acute respiratory distress syndrome (RELAx) – a multicenter 
randomized controlled trial 
 
Protocol ID 
RELAx 
Short title 
Restricted versus liberal positive end–expiratory pressure 
Version 
6.2 
Date 
December 6, 2019 
Coordinating 
investigators of 
the trial 
A.G. Algera, MD 
Department of Intensive Care 
Room C3–311 
Academic Medical Center 
Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands 
Telephone: +31 20 5666328 
E–mail: a.g.algera@amc.uva.nl 
& 
L. Pisani, MD 
Department of Intensive Care 
Room C3–423 
Academic Medical Center 
Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands 
Telephone: +31 20 5669111 
E–mail: luigipisani@gmail.com 
Principal 
investigators of 
the trial 
 
 
 
 
 
 
 
 
 
 
 
 
 
Local 
investigators in 
participating 
centers 
F. Paulus, PhD 
Department of Intensive Care 
Room C3–323 
Academic Medical Center 
Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands 
Telephone: +31 205662739 
E–mail: f.paulus@amc.uva.nl 
& 
Prof. M.J. Schultz, MD PhD 
Department of Intensive Care 
Room C3–423 
Academic Medical Center 
Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands 
Telephone: +31 205662509 
E–mail: m.j.schultz@amc.uva.nl 
 
Prof. B.J.M. van der Meer, MD PhD 
Department of Intensive Care 
Amphia Hospital 
Molengracht 21, 4818 CK Breda, The Netherlands 
Telephone +31 76 5955000 
E–mail: bvandermeer@amphia.nl 
 
P.E. Spronk, MD PhD 
Department of Intensive Care 
Gelre Hospitals, location Lucas 
Albert Schweitzerlaan 31, 7334 DZ Apeldoorn, The Netherlands 

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Telephone: +31 55 5818181 
E–mail: p.spronk@gelre.nl 
 
J.J. Haringman, MD PhD 
Department of Intensive Care 
Isala Clinics 
Dokter van Heesweg 2, 8025 AB Zwolle, The Netherlands 
Telephone: +31 38 4248410 
E–mail l: j.haringman@isala.nl 
 
D.C.J.J. Bergmans, MD PhD 
Department of Intensive Care 
Maastricht University Medical Center 
P. Debyeplein 25, 6229 HX Maastricht, The Netherlands 
Telephone: +31 43 3876385 
E–mail: d.bergmans@mumc.nl  
 
M. Slabbekoorn, MD 
Department of Intensive Care 
Haaglanden Medical Center 
Lijnbaan 32, 2512 VA Den Haag, The Netherlands 
Telephone: +31 88 9792119 
E–mail: m.slabbekoorn@haaglandenmc.nl 
 
I. Purmer, MD 
Department of intensive Care 
HagaZiekenhuis 
Leyweg 275, 2504 LN Den Haag, The Netherlands 
Telephone: +31 70 210 0000 
E–mail: i.purmer@hagaziekenhuis.nl  
 
H. Endeman, MD PhD 
Department of Intensive Care 
Onze Lieve Vrouwe Gasthuis 
Oosterpark 9, 1091 AC Amsterdam, The Netherlands 
Telephone: +31 20 5993007 
E–mail: h.edeman@olvg.nl 
 
F. Bosch, MD PhD 
Department of Intensive Care 
Rijnstate,  
Wagnerlaan 55, 6815 AD Arnhem, The Netherlands 
Telephone: +31 88 0058888 
E–mail: fhbosch@rijnstate.nl  
 
S. den Boer, MD 
Department of Intensive Care 
Spaarne Gasthuis 
Spaarnepoort 1, 2134 TM Hoofddorp, The Netherlands 
Telephone: +31 23 2246015 

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E–mail: sboer@spaarneziekenhuis.nl  
 
H.S. Moeniralam, MD PhD 
Department of Intensive Care 
Sint Antonius Hospital 
Koekoeslaan 1, 3430 EM Nieuwegein, The Netherlands 
Telephone: +31 88 3204729 
E–mail: h.moeniralam@antoniusziekenhuis.nl 
 
P.R. Tuinman, MD PhD 
Department of Intensive Care 
VU Medical Center 
De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands 
Telephone: +31 20 4442061 
E–mail: p.tuinman@vumc.nl 
 
A. Tacx, MD  
Department of Intensive Care 
Westfriesgasthuis 
Maelsonstraat 3, 1624 NP Hoorn, The Netherlands 
Telephone: +31 229 25779 
E–mail: a.tacx@westfriesgasthuis.nl 
Sponsor 
Academic Medical Center 
University of Amsterdam 
Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands 
Subsidizing party 
Zorgonderzoek–Medische Wetenschappen  
Laan van Nieuw Oost–Indië 334, 2593 CE Den Haag, The 
Netherlands 
Telephone: +31 70 3495111 
E–mail: info@zonmw.nl 
Independent 
physician per 
each center 
W.K. Lagrand, MD PhD 
Department of Intensive Care 
Room C3–430 
Academic Medical Center 
Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands 
Telephone: +31 20 62157 
E–mail: w.k.lagrand@amc.uva.nl  
 
 
 

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SIGNATURE SHEET OF STEERING COMMITTEE MEMBERS 
 
Core Steering Committee Members 
Other Steering Committee Members 
A.G. Algera, MD, Academic Medical  
Center, University of Amsterdam 
 
……………………… date ……………… 
C.A.J.M. de Borgie, PhD, Academic 
Medical Center, University of Amsterdam 
 
……………………… date ……………… 
L. Pisani, MD, Academic Medical  
Center, University of Amsterdam 
 
……………………… date ……………… 
T. Cherpanath, MD PhD, Academic 
Medical Center, University of Amsterdam 
 
……………………… date ……………… 
F. Paulus, PhD, Academic Medical  
Center, University of Amsterdam 
 
……………………… date ……………… 
R.M. Determann, MD PhD, 
Westfriesgasthuis 
 
……………………… date ……………… 
Prof. M.J. Schultz, MD PhD, Academic 
Medical Center, University of 
Amsterdam 
……………………… date ……………… 
Prof. A.M. Dondorp, MD PhD, Madihol 
Oxford Research Unit (MORU) 
 
……………………… date ……………… 
Prof. M. Gama de Abreu, MD, 
Universitätsklinikum Carl Gustav Carus 
 
……………………… date ……………… 
D.A. Dongelmans, MD MSc PhD, 
Academic Medical Center, University of 
Amsterdam 
……………………… date ……………… 
Prof. P. Pelosi, MD, IRCCS San 
Martino IST, University of Genoa 
 
……………………… date ……………… 
M.P. Merkus, PhD, Academic Medical 
Center, University of Amsterdam 
 
……………………… date ……………… 
Prof. A. Serpa Neto, MD MSc, Hospital 
Israelita Albert Einstein 
 
……………………… date ……………… 
P.R. Tuinman, MD PhD, VU Medical 
Center, VU University Amsterdam 
 
……………………… date ……………… 
 
 
Note. Although the Steering Committee Members consists of Dutch and international 
members, RELAx–trial is a randomized controlled trial in the Netherlands. 
 
 
 
 

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PROTOCOL SIGNATURE SHEET 
Name 
Signature 
Date 
Head of Department (AMC) 
Prof. M.B. Vroom, MD PhD 
 
 
 
Principal Investigator 
Prof. M.J. Schultz, MD PhD 
 
 
 
 
 
 

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TABLE OF CONTENTS 
 
1. INTRODUCTION AND RATIONALE .................................................................... 12 
1.1 Mechanical ventilation associated lung injury............................................................. 12 
1.2 Pulmonary effects of PEEP ........................................................................................ 12 
1.3 Non–pulmonary effects of PEEP ................................................................................ 12 
1.4 Systematic review and metaanalysis of RCTs of PEEP ............................................. 13 
1.5 Is there benefit of intraoperative PEEP? .................................................................... 13 
1.6 An historical perspective ............................................................................................ 13 
1.7 Current PEEP practice in ICU patients without ARDS ................................................ 14 
1.8 Need for a new RCT of PEEP in patients without ARDS ............................................ 14 
1.9 The RELAx trial ......................................................................................................... 15 
2. OBJECTIVES AND HYPOTHESIS ....................................................................... 16 
2.1 Objectives .................................................................................................................. 16 
2.1.1 Primary objective ................................................................................................ 16 
2.1.2. Secondary objectives ......................................................................................... 16 
2.2 Hypothesis ................................................................................................................. 16 
2.2.1 Primary hypothesis ............................................................................................. 16 
2.2.2. Secondary hypotheses ...................................................................................... 16 
3. STUDY DESIGN ................................................................................................... 17 
4. STUDY POPULATION ......................................................................................... 18 
4.1 Population ................................................................................................................. 18 
4.2 Inclusion criteria ......................................................................................................... 18 
4.3 Exclusion criteria ....................................................................................................... 18 
4.4 Sample size ............................................................................................................... 21 
5. INTERVENTIONAL TREATMENT OF SUBJECTS .............................................. 23 
5.1 Randomization to the ‘restricted PEEP’–arm or the ‘liberal PEEP’–arm ..................... 23 
5.2 The ‘restricted PEEP’–arm ......................................................................................... 23 
5.3 The ‘liberal PEEP’–arm .............................................................................................. 24 
6. STANDARD TREATMENT OF SUBJECTS ......................................................... 27 
6.1 Standard ventilatory management ............................................................................. 27 
6.2 Oxygenation targets ................................................................................................... 27 
6.3 Ventilator settings when a patient develops ARDS .................................................... 28 
6.4 Ventilator settings when a patient requires ECMO ..................................................... 28 
6.5 Weaning .................................................................................................................... 28 
6.6 Tracheostomy ............................................................................................................ 28 
6.7 Sedation protocol ....................................................................................................... 29 
6.8 Non–ventilatory management .................................................................................... 29 
6.8.1 Selective oropharyngeal– or digestive tract decontamination .............................. 29 
6.8.2 Thrombosis prophylaxis ...................................................................................... 29 
6.8.3 Fluid regimens .................................................................................................... 30 
6.8.4 Nutrition .............................................................................................................. 30 
7. METHODS ............................................................................................................ 31 
7.1 Study parameters/endpoints ...................................................................................... 31 
7.1.1 Main study parameter ......................................................................................... 31 
7.1.2 Secondary study parameters .............................................................................. 31 
7.1.3 Other study parameters ...................................................................................... 31 
7.3 Study procedures ...................................................................................................... 32 
7.4 Data collection ........................................................................................................... 32 
7.4.1. Other data to be collected .................................................................................. 34 
7.5 Withdrawal of individual subject ................................................................................. 34 

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7.6 Follow up of subject withdrawn from the study ........................................................... 35 
7.7 Replacement of individual subjects when deferred consent could not be obtained .... 35 
8. SAFETY REPORTING ......................................................................................... 36 
8.1 Temporary halt for reasons of subject safety ............................................................. 36 
8.2 Secondary endpoints for safety ................................................................................. 36 
8.3 Data Safety Monitoring Board (DSMB) ...................................................................... 36 
9. STATISTICAL ANALYSIS .................................................................................... 38 
9.1 General considerations .............................................................................................. 38 
9.2 Primary study parameter ........................................................................................... 38 
9.3 Secondary study parameter(s) ................................................................................... 38 
9.4 Cost–effectiveness analysis ....................................................................................... 39 
9.4.1 Cost–analysis and time horizon of the analysis ................................................... 39 
9.4.2 Measurements .................................................................................................... 39 
9.4.3 Unit costs ............................................................................................................ 39 
9.4.4. Statistical analysis of Cost–effectiveness ........................................................... 40 
9.5 Budget Impact Analysis (BIA) .................................................................................... 40 
10. ETHICAL CONSIDERATIONS ........................................................................... 41 
10.1 Regulation statement ............................................................................................... 41 
10.2 Recruitment and consent ......................................................................................... 41 
10.2.1 Deferred consent .............................................................................................. 41 
10.2.2 Ethical aspects .................................................................................................. 43 
10.2.3 No deferred consent in patients who die before obtaining informed  consent .... 44 
10.2.4 Conclusion deferred consent ............................................................................ 44 
10.3 Benefits and risks assessment, group relatedness .................................................. 45 
10.4 Compensation of injury ............................................................................................ 45 
11. ADMINISTRATIVE ASPECTS, MONITORING AND PUBLICATION ................. 46 
11.1 Handling and storage of data and documents .......................................................... 46 
11.2 Monitoring and Quality Assurance ........................................................................... 46 
11.3 Amendments ........................................................................................................... 46 
11.4 Annual progress report ............................................................................................ 46 
11.5 End of study report .................................................................................................. 46 
11.6 Public disclosure and publication policy ................................................................... 47 
12. PUBLICATION POLICY ...................................................................................... 48 
13. REFERENCES ................................................................................................... 49 
 
 
 
 

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ABBREVATIONS AND DEFINITIONS 
ARDS 
Acute Respiratory Distress Syndrome 
CE 
Cost–Effective 
DSMB 
Data Safety Monitoring Board 
ICU 
Intensive Care Unit 
LOS 
Length Of Stay 
METC 
Medical Research Ethical Committee (MREC) in Dutch: Medische 
Ethische Toetsings Commissie 
NAS 
Nurse & Activity Score 
PBW 
Predicted Body Weight 
PEEP 
Positive End–Expiratory Pressure 
RCT 
Randomized Controlled Trial 
SAE 
Serious Adverse Event 
Sponsor 
The party that commissions the organization or performance of the 
research, for example a pharmaceutical company, academic 
hospital, scientific organization or investigator; a party that provides 
funding for a study bus does not commission is not regarded as the 
sponsor, but referred to as a subsidizing party 
TISS 
Therapeutic Intervention Scoring System 
VFD–28 
Ventilator–Free Days and alive at day 28 
 
 

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SUMMARY 
Rationale: While there is sufficient randomized controlled trial–evidence for benefit of 
higher levels of positive end–expiratory pressure (PEEP) during ventilation of intensive 
care unit (ICU) patients with acute respiratory distress syndrome (ARDS), evidence for 
benefit of PEEP, at any level, during ventilation of ICU patients without ARDS is still 
insufficient. One recent metaanalysis suggests no benefit of PEEP in ICU patients 
without ARDS. Nevertheless, there is a trend to use higher PEEP levels in these 
patients in recent years. 
Hypothesis: We hypothesize that ventilation with the lowest possible PEEP level 
(‘restricted PEEP’, i.e., the lowest PEEP level resulting in an acceptable level of 
oxygenation) is as effective and safe as ventilation with the PEEP level currently 
practiced (‘liberal PEEP’, i.e., a PEEP level of 8 cm H2O, the median PEEP level 
applied in these patients in the Netherlands) in ICU patients without ARDS. 
Objective: To compare ventilation with the lowest possible PEEP level to ventilation 
with the PEEP level currently practiced in ICU patients without ARDS. 
Study design: National multicenter, non–inferiority, open, randomized controlled trial 
in intubated and ventilated adult ICU patients without ARDS. 
Study population: Consecutive intubated and ventilated adult ICU patients without 
ARDS with an anticipated duration of ventilation of at least 24 hours. 
Procedure: Patients are randomly assigned in a 1:1 ratio to the ‘restricted PEEP’–arm 
or to the ‘liberal PEEP’–arm of this trial. 
Study endpoints: The primary endpoint is the number of ventilator–free days and 
alive at day 28. Secondary endpoints include ICU– and hospital length of stay (LOS), 
ICU– and hospital, and 90–day mortality, incidence of severe hypoxemia, severe 
atelectasis and the need for rescue therapies, pneumonia, pneumothorax, the 
incidence and development of ARDS and days with use of hemodynamic support and 
with use of sedation. Also, therapeutic intervention scoring system (TISS)/ Nursing 
Activities Score (NAS) and related healthcare costs will be estimated and compared. 
Nature and extent of the burden and risks associated with participation, benefit 
and group relatedness: Differences in burden and risk of the two ventilation 
strategies are uncertain. Ventilation with the lowest possible PEEP level could increase 
the risk of atelectasis and also the risk of potentially dangerous hypoxemia, which can 
be adequately treated within the ICU setting. Ventilation with the PEEP level currently 
practiced could increase the amount of overdistended lung tissue and increase 

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hemodynamic compromise. No other study interventions are performed. Collection of 
demographic data, ventilation data and outcome data causes no harm for the patients. 

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1. INTRODUCTION AND RATIONALE 
1.1 Mechanical ventilation associated lung injury 
Mechanical ventilation is typically seen as a life–saving intervention in critically ill 
patients, despite increasing and unequivocal evidence that it can aggravate and even 
initiate lung injury.1 Indeed, ventilation may contribute to development of atelectasis,2,3 
increasing the risk of repetitive opening and closing of lung tissue, a phenomenon 
frequently referred to as ‘atelectrauma’.1 Results from preclinical studies using 
animals4,5 and studies in humans6,7 support the use of positive end–expiratory 
pressure (PEEP) during ventilation to prevent, or at least minimize the risk of 
atelectrauma. Ventilation with PEEP, however, can also lead to lung injury due to 
overdistension,8,9 frequently referred to as ‘volutrauma’.1 
1.2 Pulmonary effects of PEEP 
Atelectasis is more extensive in patients with the acute respiratory distress syndrome 
(ARDS) than in patients without lung injury, and are more frequently seen with 
mandatory than spontaneous forms of ventilation.10,11 In patients with ARDS, seen the 
balance between the positive effects of higher PEEP levels (i.e., reduction in 
atelectrauma, by reducing atelectasis) and negative effects of higher PEEP levels (i.e., 
increase in volutrauma, by increasing overdistension), ventilation with a higher PEEP 
level could result in a net beneficial effect. In patients without ARDS, however, patients 
who also more frequently receive spontaneous forms of ventilation, the balance 
between benefit and harm could go into the other direction, as the reduction in 
atelectrauma could be minimal or negligible, at a price of more volutrauma. 
The results of one metaanalysis using the individual patient data from three 
large randomized controlled trials (RCTs) comparing higher to lower PEEP levels 
during ventilation of patients with ARDS suggests benefit of higher PEEP levels (albeit 
only in patients with more severe form of ARDS).12-15 Sufficiently large RCTs 
comparing higher to lower PEEP levels during ventilation of patients without ARDS are 
presently lacking, and the available data does not allow individual patient data 
metaanalyses.16 
1.3 Non–pulmonary effects of PEEP 
Besides increasing lung aeration, ventilation with PEEP could also have 
extrapulmonary effects. Ventilation with PEEP affects the loading conditions of the 
heart,17 as every increase in intrathoracic pressure reduces the preload of the heart 

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and might increase as well as decrease the afterload of the right ventricle depending 
on whether lung tissue is recruited by PEEP.17 The effects of ventilation with PEEP on 
cardiac performance could also differ between patients with ARDS and patients without 
lung injury. Ventilation with higher PEEP levels could reduce right ventricle afterload 
through the prevention of atelectases in ARDS patients, while it could increase right 
ventricle afterload and reduce left ventricle preload through increases in overdistended 
lung tissue in patients without ARDS. RCTs evaluating the extrapulmonary effects of 
PEEP are lacking, both in ventilated patients with ARDS, and ventilated patients 
without ARDS. 
1.4 Systematic review and metaanalysis of RCTs of PEEP 
A recent systematic review and metaanalysis of RCTs in patients without ARDS did 
not find benefit from ventilation with higher PEEP levels with regard to mortality and 
duration of ventilation, neither in surgical ICU patients nor in medical ICU patients.16 
The analysis even suggested no benefit of any level of PEEP in these patients. There 
were no differences found in the incidence of hypotension and blood pressure levels 
between ventilation with higher PEEP levels versus lower PEEP levels. 
1.5 Is there benefit of intraoperative PEEP? 
The effects of PEEP during ventilation gained also interest from anesthesiologists, who 
struggle with the same question of whether or not to use PEEP in surgery patients 
without lung injury. Three RCTs showed that ventilation with PEEP combined with low 
tidal volumes was associated with better outcomes compared to ventilation without or 
a low level of PEEP combined with high tidal volumes.18-20 These RCTs thus studied 
the effect of a bundle of ventilator settings that are both expected to have an effect on 
the lungs, and it is impossible to conclude which part of the bundle was responsible for 
the benefit found. A more recent RCT, however, showed no difference in the incidence 
of pulmonary complication when no PEEP was compared to PEEP during ventilation 
at low tidal volumes.21 Furthermore, one individual patient metaanalysis using data 
from all four RCTs mentioned above suggests that benefit seemed to come mainly 
from restrictions in tidal volume size, and not from using higher levels of PEEP, in 
patients undergoing intraoperative ventilation during general anesthesia for surgery.22 
1.6 An historical perspective 
In the early years of mechanical ventilation, PEEP was seldom used because of its 
alleged negative effects on hemodynamics.23 Most RCTs of PEEP in ICU patients 

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without ARDS compared ventilation with some level of PEEP to no PEEP (figure 1). 
In the 1960s, Ashbaugh observed that PEEP improved oxygenation in mechanically 
ventilated patients with ARDS, triggering the use of PEEP in patients with this life–
threatening complication of critical illness.24 In the 1970s, animal experiments 
suggested that prophylactic PEEP could be beneficial as well,25-27 maybe even 
preventing development of ARDS.28,29 Since then PEEP is increasingly used, also in 
patients without ARDS, despite evidence for benefit of this strategy. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1.7 Current PEEP practice in ICU patients without ARDS 
Due to absence of RCT–evidence, it is highly uncertain what the best PEEP level is in 
ICU patients without ARDS. Interestingly, there is a salient tendency to use higher 
PEEP levels in these patients.30-32 Even more surprising, in the Netherlands ICU 
patients without ARDS are ventilated with a median PEEP level of 8 cm H2O, higher 
compared to a PEEP level of 6 cm H2O in surrounding countries,33 and what is reported 
to be used worldwide.34 
1.8 Need for a new RCT of PEEP in patients without ARDS 
While guidelines recommend using higher PEEP levels in ICU patients with ARDS, 
recommendations regarding the PEEP level to use in ICU patients without lung injury 
1980
1990
2000
2010
0
5
10
15
20
Year of Publication
PEEP (cm H2O)
High PEEP
Low PEEP
Figure 1. PEEP levels in randomized controlled trials in patients 
without ARDS.16 

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are lacking. Often a minimum PEEP level of 5 cm H2O is recommended, though this is 
without any scientific support. Consequently, the ICU community requests a well–
powered high–quality RCT comparing ventilation with higher versus lower PEEP levels 
in ICU patients without ARDS.16 This RCT should use objective and patient–relevant 
outcomes, such as duration of ventilation and ICU– and hospital length of stay (LOS), 
amongst others. 
1.9 The RELAx trial 
The ‘REstricted versus Liberal positive end–expiratory pressure in patients without 
Acute respiratory distress syndrome’ (RELAx) trial is a national multicenter open 
randomized controlled trial in ICU patients without ARDS at start of ventilation. It will 
be the first RCT comparing ventilation with the lowest possible PEEP level with 
ventilation with the median PEEP level currently practiced in the Netherlands that 
recruits a sufficient number of patients to test the hypothesis that ventilation with the 
lowest possible PEEP level is non–inferior to ventilation with a PEEP level of 8 cm H2O 
with regard to objective and patient–relevant clinical endpoints. 
 
 

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2. OBJECTIVES AND HYPOTHESIS 
2.1 Objectives 
2.1.1 Primary objective 
The aim of the RELAx trial is to compare ventilation with the lowest possible PEEP 
level (‘restricted PEEP’, i.e., the lowest PEEP level resulting in an acceptable level of 
oxygenation) to ventilation with the PEEP level currently practiced (‘liberal PEEP’, i.e., 
a PEEP level of 8 cm H2O, the median PEEP level in these patients in the Netherlands) 
in intubated and ventilated ICU patients not fulfilling the consensus definition for ARDS 
at start of ventilation. 
2.1.2. Secondary objectives 
Secondary objectives are to compare the effects of ‘restricted PEEP’ vs. ‘liberal PEEP’ 
on ICU– and hospital length of stay (LOS), ICU– and hospital, and 90–day mortality, 
the incidence of severe hypoxemia, severe atelectasis, and the need for rescue 
therapies including recruitment maneuvers, bronchoscopy and prone position, 
pneumonia, pneumothorax, the incidence and development of ARDS, days with use 
of hemodynamic support and with use of sedation, therapeutic intervention scoring 
system (TISS)/ Nursing Activities Score (NAS) and related healthcare costs. 
2.2 Hypothesis 
2.2.1 Primary hypothesis 
We hypothesize that ventilation with the lowest possible PEEP level results in a similar 
number of ventilator–free days at day 28 as ventilation with the PEEP level currently 
practiced in ICU patients without ARDS. 
2.2.2. Secondary hypotheses 
The secondary hypotheses are that ventilation with the lowest possible PEEP level is 
equal to ventilation with the PEEP level currently practiced in ICU patients without 
ARDS, with regard to the other endpoints mentioned above. 

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3. STUDY DESIGN 
The RELAx trial is a national multicenter, non–inferiority, open, randomized controlled 
trial in intubated and ventilated adult ICU patients without ARDS expected to need 
ventilation for at least 24 hours. A total of 980 ICU patients in 12 participating academic 
as well as non–academic centers will be included. 
 
 

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4. STUDY POPULATION 
4.1 Population 
The RELAx trial will recruit consecutive intubated and mechanically ventilated ICU 
patients without ARDS at onset of ventilation and who are expected to need ventilation 
> 24 hours. Patients are included in the ICUs of 3 academic and 9 non–academic 
centers in the Netherlands. Patients are screened for eligibility and randomized within 
one hour after initiation of invasive ventilation or, if already intubated and ventilated 
before admission, on ICU admission. A total of 980 patients will be randomized; 
approximately 82 patients per center. 
4.2 Inclusion criteria 
In order to be eligible to participate in this trial, patients must meet all of the following 
criteria: 
 Admission to one of the participating ICUs 
 Need for and start of invasive ventilation 
 An expected duration of ventilation > 24 hours 
4.3 Exclusion criteria  
Patients who meet any of the following criteria will be excluded: 
 Age less than 18 years 
 Patients with a clinical diagnosis of ARDS or possible ARDS with a PaO2/FiO2 < 
200 mmHg (as the benefit of ventilation with higher PEEP levels has been proven 
in these patients; see text box 1) 
 Patients with ongoing cardiac ischemia due to cardiac infarction and failed 
revascularization, patients with increased and uncontrollable intracranial pressure 
(of ≥ 18 mmHg), patients with delayed cerebral ischemia after subarachnoid 
hemorrhage, patients with necrotizing fasciitis, and severe untreatable anemia 
such as in case of Jehovah’s Witnesses (as these patients can be considered to 
be vulnerable to the potentially dangerous hypoxemia which could develop more 
often, even for a short time, in the ‘restricted PEEP’–arm of this trial; see text box 
2) 
 Patients previously randomized in this RCT 
 Patients participating in another RCT with the same clinical endpoint, or 
interventions possibly compromising the primary outcome 

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 Invasive ventilation longer than 12 hours directly preceding the present ICU 
admission 
 Invasive ventilation longer than 1 hour before randomization 
 Patients with suspected or confirmed pregnancy 
 Patients with morbid obesity (body mass index > 40) 
 Patients with GOLD classification III or IV chronic obstructive pulmonary disease 
(COPD) 
 Patients with premorbid restrictive pulmonary disease (evidence of chronic 
interstitial infiltration on chest radiographs) 
 Patients in whom pulse oximetry is known to be unreliable, e.g., patients with 
carbon monoxide poisoning 
 Any neurologic diagnosis that can prolong duration of mechanical ventilation, e.g., 
patients with Guillain–Barré syndrome, high spinal cord lesion or amyotrophic 
lateral sclerosis, multiple sclerosis, or myasthenia gravis 
 Patients receiving veno-venous, veno-arterial or arterio-venous extracorporeal 
membrane oxygenation (ECMO) 
 No informed consent 

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Text Box 1 – Diagnosing ARDS 
The diagnosis of ARDS is clinical, requiring (a) a medical history, (b) the presence 
of bilateral opacities on the chest radiograph that are fully explained by effusions, 
lobar/lung collapse or nodules, and (c) respiratory failure not fully explained by 
cardiac failure or fluid overload. The PaO2/FiO2 is used to classify ARDS severity, 
with a PaO2/FiO2 between 200 and 300 mmHg indicating mild ARDS, and a 
PaO2/FiO2 < 200 mm Hg indicating moderate or severe ARDS. 
The diagnostic approach, however, could be difficult if not impossible in ICU 
patients within the first hour after intubation and start of ventilation: they frequently 
suffer from temporary post–intubation atelectasis as a reason for a low PaO2/FiO2, 
the medical history is often not yet complete, and imaging studies are usually not 
yet performed or the results available. The risk is that only the PaO2/FiO2 is used 
to diagnose ARDS in the short time frame after intubation, which could induce 
severe bias, as many of these patients do not have ARDS. 
Thus, we exclude all patients that are clinically diagnosed with ARDS. Patients 
with a PaO2/FiO2 < 200 mm Hg are also excluded since we consider these 
patients at high risk of having ARDS; only when the attending physician explicitly 
states the patients has no ARDS and no direct risk factor for ARDS is present, the 
patient can be included. Patients without ARDS and with a PaO2/FiO2 between 200 
and 300 mmHg can be included: as these patients very seldom have ARDS. 

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4.4 Sample size 
Group size calculation is focused on demonstrating non–inferiority. When the sample 
size in each is 445, an one–sided non–inferiority t–test (targeted at 0.05 significance 
level) for the difference in means of log–transformed normalized data has a 80% power 
to reject the null hypothesis that the number of VFD–28 in the ‘restricted PEEP’–arm 
is inferior to the number of VFD–28 in the ‘liberal PEEP’–arm by a margin of 10% 
anticipating on a coefficient of a variation of 0.70 (www.stichting–nice.nl), in favor or 
the alternative hypothesis that the number of VFD–28 in the ‘restricted PEEP’–arm is 
non–inferior. 
The choice for a margin of 10% is motivated by what we consider acceptable 
from a clinical point of view as the maximal acceptable reduction of the ventilator–free 
period for non–inferiority. Clinically this margin means that an increase of > 10% in the 
Text Box 2 – Potentially vulnerable patients 
Oxygen delivery to the tissues (DO2) depends on cardiac output and arterial blood 
oxygen content,35 the latter being dependent on hemoglobin saturation, arterial 
blood oxygen saturation (SaO2) and partial pressure of oxygen (PaO2). The 
understanding of the importance of the several components of DO2 has led to 
emphasize early identification and prevention of hypovolemia (to prevent a low 
cardiac output) and anemia, but also prevention of hypoxemia for critically ill 
patients. 
Administration of fluids, packed red blood cells, and additional oxygen could all be 
useful, though the effect size on DO2 differs substantially. Indeed, a 50%–decrease 
in hemoglobin concentration (e.g., from 9 to 4,5 mmol/l) results in a 50% reduction 
of DO2, whereas a 50%–reduction in the PaO2 (e.g., from 12 to 6 kPa, or SaO2 
(from 98 to 78%) results only in no more than 20% decrease in DO2. Thus, the 
influence of a drop in hemoglobin concentration is of greater influence on DO2 as 
compared to a drop in PaO2 or SaO2. 
Nevertheless, the targeted O2 saturation proposed in this RCT could potentially be 
harmful in certain patient groups, like those with proven ongoing cardiac ischemia 
or delayed cerebral ischemia, or necrotizing fasciitis, or severe untreatable anemia 
such as in case of Jehovah’s Witnesses. Therefore, these patients should be 
excluded form participation in this trial. 

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duration of mechanical ventilation will reduce the VFD–28 with > 12 hours (calculated 
over the expected mean duration of mechanical ventilation of 5 days) 
(http://www.stichting–nice.nl) which will be considered inferior. To allow for an 
anticipated drop out of 10% a total of 980 patients will be included. 
 
 

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5. INTERVENTIONAL TREATMENT OF SUBJECTS 
5.1 Randomization to the ‘restricted PEEP’–arm or the ‘liberal PEEP’–arm 
Patients are randomly assigned in a 1:1 ratio to the ‘restricted PEEP’–arm or to the 
‘liberal PEEP’–arm of this trial. 
5.2 The ‘restricted PEEP’–arm 
Directly after start of invasive ventilation the PEEP level is set at 5 cm H2O with an 
inspired oxygen fraction (FiO2) between 0.21 and 0.6. The goal is to ventilate with the 
lowest possible PEEP level resulting in an acceptable level of oxygenation. For this, 
the operator, usually the attending ICU nurse, will reduce the level of PEEP in steps of 
1 cm H2O to a minimum level of 0 cm H2O. Every 15 minutes the PEEP level is reduced 
with 1 cm H2O, as long as the pulse oximetry reading shows a SpO2 > 92% or the 
arterial blood gas shows a PaO2 > 8 kPa, as illustrated in the flowchart (see Figure 1). 
Thereafter, ventilation continues with the lowest PEEP level at which the SpO2 > 92% 
or PaO2 > 8 kPa, using a FiO2 of between 0.21 and 0.6. In case the SpO2 drops below 
92% or the PaO2 drops below 8 kPa, brief periods of 5 minutes may be tolerated, first 
FiO2 is increased up to maximum 0.6 before the level of PEEP is increased in steps of 
1 cm H2O until 5 cm H2O. As soon as the patient stabilizes, again the level of PEEP is 
reduced in steps of 1 cm H2O to a minimum level of 0 cm H2O. 
So–called ‘down–titrations’ of the PEEP level are allowed as often as wanted, 
but with a minimum of three ‘down–titrations’ per ICU nurse shift (i.e., every eight 
hours). This number is chosen to push nurses towards using the lowest possible PEEP 
level. We deliberately chose not to state a maximum for these ‘down–titrations’, as 
adjustments in ventilator settings, like FiO2 and driving pressure, in the Dutch ICU 
setting are very frequent, occurring many more times than three times per shift – this 
is a safe process, and we assume it is the same for the PEEP level adjustments. 
Patients are weaned from the ventilator (see: weaning) and tracheally extubated 
using the lowest PEEP level. In other words, the lowest PEEP level is used throughout 
the complete period of invasive ventilation. However, during pulmonary toileting and 
tracheal suctioning, bronchoscopic procedures, intra– or inter–ICU transport or any 
maneuver during which ‘pre–oxygenation’ with high FiO2 is deemed beneficial, ICU 
nurses are allowed to increase the FiO2 > 0.6, and preferably not the level of PEEP. 
Pulmonary rescue: in case of severe hypoxemia, defined as a drop in SpO2 
below 88% or a drop in PaO2 below 7.3 kPa, common causes such as a mucus plug 

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requiring pulmonary toilet should be considered and treated, the FiO2 level is increased 
up to 1.0 and the PEEP level is set back at 5 cm H2O or more, both to a level left to 
the discretion of the attending physician. After solving the cause for the drop in SpO2 
or PaO2, the PEEP level is again ‘down–titrated’, following the same steps as described 
above. Development of atelectasis, or increases in the amount of atelectasis is not 
necessarily a reason for using a higher PEEP level, unless the SpO2 drops below 92% 
or the PaO2 drops below 8 kPa, and does not respond to increases in FiO2 to maximal 
0.6. If a patient develops ARDS, according to the Berlin definition for ARDS,36,37 the 
level of PEEP should always be increased to 10 cm H2O, or more. 
Hemodynamic rescue: in case a patient becomes hemodynamic unstable, 
meaning that more inotropes and/or vasoactive agents are needed, hemodynamic 
compromise due to increases in atelectasis could be considered. Then, for a short 
period of time (e.g., for 1 to 2 hours) the PEEP level can be set at 5 cm H2O. After 
solving the hemodynamic problem, the PEEP level is again ‘down–titrated’. 
5.3 The ‘liberal PEEP’–arm 
Directly after start of invasive ventilation the PEEP level is set at 8 cm H2O with a FiO2 
between 0.21 and 0.6. The goal is to ventilate the patient mainly at this level of PEEP 
till tracheal extubation. For this, the operator will increase the level of PEEP, if a level 
of < 8 cm H2O was used, to 8 cm H2O in one single step (see Figure 1). Thereafter, 
ventilation continues with the PEEP level at 8 cm H2O using a FiO2 of between 0.21 
and 0.6. In case the SpO2 drops below 92% or the PaO2 drops below 8 kPa, first FiO2 
is increased to maximum 0.6 before the level of PEEP is further increased. 
Patients are weaned of the ventilator (see: weaning) and tracheally extubated 
using a PEEP level of 8 cm H2O. However, during pulmonary toileting and tracheal 
suctioning, bronchoscopic procedures, intra– or inter–ICU transport or any maneuver 
during which ‘pre–oxygenation’ with high FiO2 is deemed beneficial, ICU nurses are 
allowed to increase the FiO2 > 0.6, and preferably not the level of PEEP. If preferred, 
the level of PEEP can be set at 5 cm H2O for one to two hours directly before tracheal 
extubation, left to the discretion of the attending physician. 
Pulmonary rescue: in case of severe hypoxemia, defined as a drop in SpO2 
below 88% or a drop in PaO2 below 7.3 kPa, common causes such as a mucus plug 
requiring pulmonary toilet can be considered and treated, FiO2 level is increased up to 
1.0 to a level left to the discretion of the attending physician, if necessary the PEEP 

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level can be increased. After solving the cause for the drop in SpO2 or the drop in PaO2, 
FiO2 and the level of PEEP is set back. 
Hemodynamic rescue: in case a patient becomes hemodynamic unstable, 
meaning that more inotropes and/or vasoactive agents are needed, hemodynamic 
compromise due to increases in overdistension could be considered. Then, for a short 
period of time (e.g., for 1 to 2 hours) the PEEP level can be set at 5 cm H2O. After 
solving the hemodynamic problem, the level of PEEP is again set back to 8 cm H2O. 
The goal is to ventilate patients in this arm with a PEEP level of 8 cm H2O and 
only to adjust the PEEP level when deemed necessary. This reflects current ventilation 
practice in the Dutch setting, where the PEEP level is further increased to improve 
oxygenation, but decreased in case of hemodynamic compromise (see Figure 1). 
 
 
 

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Figure 1. Flowchart ventilator settings in the ‘restricted PEEP’–arm and in the ‘liberal PEEP’–arm 
 
 
Abbreviations: PEEP, positive end–expiratory pressure; MV, mechanical ventilation; PBW, predicted body weight; ARDS, acute 
respiratory distress syndrome.  
In APPENDIX III a few patient examples are shown to clarify and explain the proposed ventilation strategy in the ‘restricted PEEP’–
arm. 

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6. STANDARD TREATMENT OF SUBJECTS 
6.1 Standard ventilatory management 
The RELAx trial allows the following ventilatory modes: volume–controlled or 
pressure–controlled ventilation, and pressure support ventilation. Automated modes, 
in particular those that automatically change the PEEP level and FiO2, are never 
allowed. 
With volume–controlled and pressure–controlled ventilation the inspiration–to–
expiration ratio is set at 1:2. With volume–controlled ventilation the inspiration time and 
pause are set at 25% and 10%, respectively. With pressure support ventilation, the 
highest possible pressure rise is chosen and cycling off is set at 25%. 
Tidal volume size is between 6–8 ml/kg predicted body weight (PBW), which is 
calculated according to the following formula38 50 + 0.91 x (centimeters of height – 
152.4) for males and 45.5 + 0.91 x (centimeters of height – 152.4) for females. The 
respiratory rate is adjusted to obtain a normal arterial blood pH (7.35 to 7.45). In case 
of metabolic acidosis or alkalosis, a lower or higher than normal PaCO2 can be 
accepted, which is left to the discretion of the attending physician. Recruitment 
maneuvers are allowed when deemed necessary, but the decision to perform a 
recruitment maneuver is also left to the discretion of the attending physician. 
6.2 Oxygenation targets 
The oxygenation target ranges for SpO2 and PaO2 are 92% to 96%, and 8 kPa to 11.5 
kPa, respectively.39-43 Oxygenation will be maintained in the target ranges primarily by 
adjusting the FiO2, which is typically set between 0.21 and 0.6. The oxygenation target 
is primarily assessed by peripheral saturation (SpO2) as measured by pulse oximetry 
and only in case of unreliable reading the oxygenation will be assessed by the arterial 
blood oxygen pressure (PaO2). 
For patients in whom the risk of potentially dangerous hypoxemia could be 
become unacceptable during the trial (e.g., in patients who develop: ongoing cardiac 
ischemia due to cardiac infarction and failed revascularization, delayed cerebral 
ischemia after subarachnoid hemorrhage, increased and uncontrollable intracranial 
pressure (of ≥ 18 mmHg), necrotizing fasciitis or severe untreatable anemia such as 
with Jehovah’s Witnesses), the oxygenation target ranges can be increased to SpO2 
and PaO2 of 94% to 96%, and 9 kPa to 11.5 kPa, respectively. 

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6.3 Ventilator settings when a patient develops ARDS 
In case a patient develops ARDS, ventilation should be continued according to existing 
guidelines for patients with ARDS. This at least consists of low tidal volumes (6 ml/kg 
PBW or lower), and higher PEEP levels (10 cm H2O or higher). Also, a low driving 
pressure could be considered. 
6.4 Ventilator settings when a patient requires ECMO 
In the unlikely event that a patient receives ECMO, the ventilator is set according to 
the local protocol for ventilation under ECMO. This means that PEEP is no longer 
titrated according to the study protocol. 
6.5 Weaning 
In all patients who receive assist ventilation, three times a day it should be tested 
whether the patient accepts assist ventilation; this should also be tried when the patient 
shows respiratory muscle activity during assist ventilation. 
The attending physician decides when to tracheally extubate a patient, based 
on general extubation criteria (i.e. responsive and cooperative, adequate cough reflex, 
adequate oxygenation with FiO2 ≤ 0.4, hemodynamically stable, no uncontrolled 
arrhythmia and a rectal temperature > 36 Celsius and after successfully passing a 
spontaneous breathing trial (SBT) with a T–piece or ventilation with minimal support 
(pressure support level < 10 cm H2O) and FiO2 ≤ 0.4. In case SBTs are used, an SBT 
is judged as successful when the following criteria are met for at least 30 minutes, the 
attending physician takes the final decision for extubation: 
 Respiratory rate < 35/min 
 Peripheral oxygen saturation > 90% 
 Increase < 20% of Heart rate and blood pressure 
 No signs of anxiety and diaphoresis 
In case a patient needs to be re–intubated and ventilated, the PEEP level is set as 
described above. 
6.6 Tracheostomy 
Early tracheostomy has no advantage over late tracheotomy.44 Therefore, 
tracheostomy is only to be performed on strict indications and preferably not earlier 
than 10 days after intubation. Strict indications for tracheostomy:  
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 Glasgow Coma Score < 7 and/or inadequate swallow or cough reflex with retention 
of sputum 
 Severe ICU–acquired weakness 
 Repeated respiratory failure after extubation 
 Pre–existent diminished pulmonary reserves 
 Failure to intubate 
 Prolonged or unsuccessful weaning 
Weaning with a tracheostomy follows recommendations as described under ‘weaning’, 
a suggested scheme for unassisted ventilation with a tracheostomy is described in 
APPENDIX II. 
6.7 Sedation protocol 
Sedation follows the local guidelines for sedation in each participating unit. In general, 
these guidelines favor the use of analgo–sedation over hypno–sedation, use of bolus 
over continuous infusion of sedating agents, and the use of sedation scores.  
Nurses determine the level of sedation at least 3 times per day. The adequacy of 
sedation in each patient is evaluated using a Richmond Agitation Sedation Scale 
(RASS).45,46 A RASS score of –2 to 0 is seen as adequate sedation. The goals of 
sedation are to reduce agitation, stress and fear; to reduce oxygen consumption (heart 
rate, blood pressure and minute volume are measured continuously); and to reduce 
physical resistance to– and fear of daily care and medical examination. Patient comfort 
is the primary goal.  
Level of pain is determined using scales such as Numeric Rating Scale (NRS), Visual 
Analogue Scale (VAS), Critical Care Pain Observation Tool (CCPOT) or Behavioral 
Pain Scale (BPS). 
6.8 Non–ventilatory management 
6.8.1 Selective oropharyngeal– or digestive tract decontamination 
To prevent nosocomial infections, selective oropharyngeal decontamination (SOD) or 
selective decontamination of the digestive tract (SDD) is performed in all patients who 
are expected to need ventilation for longer than 48 hours, and/or are expected to stay 
in ICU for longer than 72 hours.47 
6.8.2 Thrombosis prophylaxis 
Thrombosis prophylaxis is indicated for all patients who are not treated with 
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implanted device or extracorporal circulation like for renal replacement therapy. 
Thrombosis prophylaxis will be given according to local guidelines. 
6.8.3 Fluid regimens 
A fluid balance targeted at normovolemia and a diuresis of ≥ 0.5 ml/kg/hour should be 
maintained. Crystalloid infusions are preferred over colloid infusions. 
6.8.4 Nutrition 
A hypo–caloric, protein–rich diet (1.2–1.7 gr/kg bodyweight /24 hours) is started as 
soon as possible after ICU admission. Enteral nutrition with a feeding gastric tube is 
preferred over intravenous feeding. If stomach retention occurs, a duodenal tube can 
be used if administration of prokinetic drugs is not sufficient, according to local 
guidelines. When optimal protein intake cannot be reached within 4 days, additional 
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7. METHODS 
7.1 Study parameters/endpoints 
7.1.1 Main study parameter 
The primary endpoint is the number of ventilator–free days and alive at day 28, defined 
as the number of days from day 1 to day 28; the patient is alive and breathes without 
assistance of the mechanical ventilator, if the period of unassisted breathing lasted at 
least 24 consecutive hours. 
7.1.2 Secondary study parameters 
Secondary study parameters include: 
 ICU length of stay (LOS) 
 Hospital LOS 
 ICU mortality 
 Hospital mortality 
 90–day mortality 
 Incidence of development ARDS (APPENDIX I) 
 Incidence of severe hypoxemia (APPENDIX I) 
 Incidence of severe atelectasis, if a chest radiograph is obtained (APPENDIX I) 
 Rescue therapies for severe hypoxemia or severe atelectasis 
o Recruitment maneuver (APPENDIX I) 
o Prone positioning 
o Bronchoscopy for opening atelectasis 
 Incidence of pneumothorax, if a chest radiograph is obtained or other kind of 
imaging suitable for diagnosing pneumothorax is obtained (APPENDIX I)  
 Incidence of pneumonia (APPENDIX I) 
 The level of PEEP in the ‘restricted PEEP’–arm and the ‘liberal PEEP’–arm 
 Days with use of hemodynamic support, defined as the number of ICU days with 
any use of vasopressors/inotropes for > 1 hour on a day  
 Days with use of sedation, defined as the number of ICU days with any use of 
sedatives for > 1 hour on a day 
 Therapeutic intervention scoring system (TISS)/ Nursing Activities Score (NAS) 
7.1.3 Other study parameters 
Health care related costs will be estimated from the health systems perspective over 
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costs of stay in hospital, costs of use of inotropes and vasopressors, costs of use of 
sedatives, costs of use of tracheostomies, costs of ventilator–associated pneumonia. 
Costs will be determined for both PEEP arms during the 28 days follow up period after 
initial ICU admission. These are used to calculate incremental cost per mechanical 
ventilation–day avoided. 
Lung ultrasound (LUS): within 12 hours after enrolment in the RELAx study, after 24-
48 hours after enrolment and within 24 hours after detubation, a LUS will be performed 
to monitor changes in lung aeration. This is only done in patients admitted to the AMC 
(see appendix IV: RELAxLUS). 
Cardiac ultrasound (ECHO): 24-48 hours after enrolment in the RELAx study, a 
transthoracic echocardiography (TTE) will be performed to assess the cardiac function. 
This is only done in a total of 68 patients admitted to the AMC (see appendix V: 
RELAxECHO).7.2 Randomization, blinding and treatment allocation 
Randomization will be performed using a dedicated, password protected, SSL–
encrypted website. Randomization sequence is generated by a dedicated computer 
randomization software program, ALEA, using random block sizes (4, 6, up to maximal 
8). Due to the nature of the treatment, blinding is not possible. 
Patients are randomly assigned in a 1:1 ratio to the ‘restricted PEEP’–arm or to the 
‘liberal PEEP’–arm of this trial. 
7.3 Study procedures 
Patients in participating intensive care units (ICU) are screened and randomized within 
1 hour after start of mechanical ventilation. Demographic data of all screened patients, 
regardless of meeting the enrollment criteria will be recorded (age, gender, expected 
duration of ventilation > or < than 24 hours). 
The oxygenation target ranges for SpO2 and PaO2 are 92% to 96%, and 8 kPa to 11.5 
kPa, respectively.39-43 Oxygenation will be maintained in the target ranges primarily by 
adjusting the FiO2, which is typically set between 0.21 and 0.6. The oxygenation target 
is primarily assessed by SpO2, as measured by pulse oximetry and only in case of 
discrepancy unreliable reading the oxygenation will be assessed by the PaO2. 
Therefore, no extra arterial blood gasses need to be obtained, besides the normally, 
3–4 daily conducted arterial blood samples. 
7.4 Data collection 
 On admission and within the first 24 hours: 

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 Gender and age (male + years) 
 Height and weight (cm + kg) 
 Reason for ICU admission 
 Reason for ventilation support 
 Cause of respiratory failure 
 APACHE II score and SAPS II score 
 Respiratory status, on admission, and every day at a fixed time point until day 28: 
 Intubation status (if extubated: time of extubation) 
 Tracheostomy status (if tracheostomized: time of tracheostomy) 
 Invasiveness of ventilation (invasive, non–invasive, or intermittent ventilation via 
tracheostomy) 
 Location of patient, every day at a fixed time point until day 28, and at day 90 (in 
ICU, hospital, other facility, or home) and life status (alive of deceased) 
 Pulmonary complication, every day at a fixed time point until day 28 or discharge 
from ICU, whatever comes first: 
 ARDS (yes or no) (APPENDIX I) 
 Severe hypoxemia (yes or no) (APPENDIX I) 
 Pneumonia (yes or no) (APPENDIX I) 
 Severe atelectasis (yes or no) (APPENDIX I) 
 Pneumothorax (yes or no) (APPENDIX I) 
 Need for rescue therapies for severe hypoxemia or severe atelectasis, every day 
at a fixed time point until day 28 or discharge from ICU, whatever comes first 
 Recruitment maneuver (yes or no) (APPENDIX I) 
 Prone positioning (yes or no) 
 Bronchoscopy for opening atelectasis (yes or no) 
 Days with use hemodynamic support, every day at a fixed time point until day 28 
or discharge from ICU, whatever comes first. Defined as the number of ICU days 
with any use of vasopressors/inotropes use for > 1 hour on a day (yes or no) 
 Days with use of sedation, every day at a fixed time point until day 28 or discharge 
from ICU, whatever comes first. Defined as the number of ICU days with any use 
of sedatives for > 1 hour on a day (yes or no) 
 ICU–acquired weakness, every day until day 28 or discharge form ICU, whatever 
comes first: Medical Research Council (MRC) score (APPENDIX I)48  

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7.4.1. Other data to be collected 
 Mechanical ventilation parameters, 1 hour before and 1 hour after randomization 
and every day at a fixed time point until liberation from the ventilator: 
 Mode of ventilation 
 Tidal volume 
 Respiratory Rate 
 Level of positive end–expiratory pressure (PEEP, cm H2O) 
 Peak and plateau pressures, or level of pressure support (level above PEEP, 
and maximal airway pressure, cm H2O) 
 Inspiration to expiration ratio 
 Inspired oxygen fraction (%) 
 Minute volume (liters/minute) 
 Respiratory parameters, 1 hour before and 1 hour after randomization, and every 
day at a fixed time point until liberation from the ventilator: 
 Peripheral oxygen saturation (%) 
 End–tidal fractions CO2 (kPa) 
 PaO2 (kPa) 
 PaCO2 (kPa) 
 Arterial bicarbonate (mmol/L) 
 Arterial pH 
 Arterial base excess (mmol/L) 
 Non–respiratory parameters, every day at fixed time point until liberation from the 
ventilator: 
 Cumulative fluid balance (ml) 
 Transfusion of blood products (type and ml)   
 Infusion of colloids (type and ml) 
 Infusion of (artificial) colloids (type and ml) 
 Sequential Organ Failure Assessment score (SOFA) score 
 Extra pulmonary infection, sepsis, re–operation, cardiac arrest 
 Therapeutic intervention scoring system (TISS)/ Nursing Activities Score (NAS) 
7.5 Withdrawal of individual subject 
Subjects can leave the trial at any time for any reason if they wish to do so without any 
consequences. 

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7.6 Follow up of subject withdrawn from the study 
Patients withdrawn from the trial will not be subjected to follow up. 
7.7 Replacement of individual subjects when deferred consent could not be 
obtained 
When deferred consent is not obtained after randomization and provisional inclusion 
of a patient, the randomized subject will be replaced. In the randomization log these 
cases will be recorded without patient–specific data. The randomization subjects will 
be replaced in order to retain properly distributed randomization groups.  
In the sample size calculation, a dropout rate of 10 % has been taken into account. 
 
 

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8. SAFETY REPORTING 
8.1 Temporary halt for reasons of subject safety 
In accordance to section 10, subsection 4, of the WMO, the sponsor will suspend the 
trial if there is sufficient ground that continuation of the trial will jeopardise subject 
health or safety. The sponsor will notify the accredited METC without undue delay of 
a temporary halt including the reason for such an action. The trial will be suspended 
pending a further positive decision by the accredited METC. The investigator will take 
care that all subjects are kept informed. 
8.2 Secondary endpoints for safety 
Since we compare two ventilation strategies that are currently used in standard care, 
additional risks are not expected. Furthermore, the study population consists of 
critically ill patients, with a high incidence of death or life–threatening events due to the 
severity of their illness (the hospital mortality in ventilated ICU patients is 21% 34). 
Therefore, we propose to report the secondary endpoints of this trial, which incorporate 
ventilation specific complications, in a line listing two times per year to the METC to 
monitor safety of both treatment strategies. The METC will receive a line listing of the 
secondary endpoints incorporating ventilation specific ventilation complications (see 
below). These endpoints will be specified per study arm in the line listing without 
disclosing the specific arms. 
Those ventilation specific complications include: 
 ICU mortality 
 Incidence of development of ARDS 
 Incidence of severe hypoxemia 
 Incidence of rescue therapy for severe hypoxemia and/or severe atelectasis: 
 Recruitment strategies 
 Prone positioning 
 Bronchoscopy for opening atelectasis  
8.3 Data Safety Monitoring Board (DSMB) 
An DSMB will be installed to monitor safety and the overall conduct of the trial. The 
DSMB will compose of 4 individuals who will be invited, one of which will be the 
chairman. 
 The DSMB will first meet after inclusion of the first 150 patients, approximately 6 
months after the first patient is enrolled.  

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 Subsequent to this meeting the DSMB will meet virtually every 6 months 
 The DSMB will review the overall status of the program, number of patients enrolled 
overall and in each center, adherence to the protocol overall and by each center. 
 The DSMB will monitor safety of both ventilation strategies by monitoring the 
secondary endpoints of ventilation specific complications.  
 The following DSMB individuals will be invited: 
 I. Martin-Loeches, MD PhD, St James’s University Hospital, Dublin, Ireland 
 P. Severgnini, MD, Universita degli Studi dell’Insubria, Varese, Italy 
 F. van Haren, MD PhD, Canberra Hospital, Garran, Australia 
 Prof. A. Artigas, MD PhD, Hospital de Sabadell, Sabadell, Spain 
The report and/or advice of the DSMB will only be sent to the sponsor of the study, the 
Academic Medical Center. Should the sponsor decide not to fully implement the advice 
of the DSMB, the sponsor will send the advice to the reviewing METC, including a note 
to substantiate why (part of) the advice of the DSMB will not be followed. 
 
 

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9. STATISTICAL ANALYSIS 
9.1 General considerations 
The statistical analysis will be based on the intention–to–treat principle. In addition, we 
will perform a per–protocol analysis to check for robustness of results. The intention–
to–treat analysis includes all patients as randomized regardless of whether they 
received the randomized treatment or other protocol deviations. Per–protocol group 
analysis only considers those patients who completed the treatment according to the 
originally allocated protocol. In this non–inferiority trial we include a superiority, primary 
effect analysis. If the non–inferiority criterion is satisfied, a secondary analysis of the 
primary endpoint for superiority will be conducted. When appropriate, statistical 
uncertainty will be expressed by the 95% confidence levels. P–values of 0.05 are used 
for statistical significance. All statistical analysis will be performed with the R version 
3.3.2. 
9.2 Primary study parameter 
The primary outcome is the number of ventilator–free days and alive at day 28 after 
ICU admission. The null hypothesis entails that ventilation with the ‘restricted PEEP’–
arm is inferior by a margin of 10% to ventilation with the ‘liberal PEEP’–arm. If the 95% 
CI upper bound for inferiority of the ‘restricted PEEP’–arm is < 10%, the null hypothesis 
of inferiority is rejected. If the non–inferiority criterion is satisfied, then a secondary 
analysis of the primary endpoint for superiority will be tested. We will use an 
appropriate nonparametric analysis method to evaluate the confidence interval for the 
difference between the two medians of the ventilator–free days from both PEEP arms. 
Additionally, time to freedom from mechanical ventilation is expressed with Kaplan–
Meier curves. Differences between both PEEP arms will be analyzed using the log–
rank test. 
9.3 Secondary study parameter(s) 
Continuous normally distributed variables will be expressed by their mean and 
standard deviation or, when not normally distributed, as medians and their interquartile 
ranges. Categorical variables will be expressed as frequencies and percentages. 
Differences between groups in continuous variables will be analyzed with Students t–
test or if continuous data is not normally distributed, the Mann–Whitney U test will be 
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exact test, as appropriate. Time–dependent data will be expressed with Kaplan–Meier 
curves. 
9.4 Cost–effectiveness analysis 
Alongside the proposed RCT a prospective economic study will be performed. The 
economic evaluation primarily focuses on the possible gained benefits of ventilation 
with the lowest possible PEEP versus ventilation with the PEEP level currently 
practiced and the associated healthcare costs within 28 days (the primary outcome of 
the RCT). 
 
Incremental Cost Effectiveness Ratios (ICER) will be calculated by extra costs 
per TISS/NAS point, a valuable score reflecting workload and resource utilization in 
daily ICU practice.49,50 Cost calculations will be based on actual performance and 
resource use in routine ICU care during the study follow–up period. 
9.4.1 Cost–analysis and time horizon of the analysis 
Cost categories and overall costs will be compared between both ventilation strategies 
and where relevant, differences will be calculated, inclusive of 95% confidence 
intervals. Additional costs as a result of comorbid conditions will be excluded. The 
economic evaluation will be set–up as a cost–effectiveness analysis (CEA). The time 
horizon will be limited to the short–term follow–up (i.e., 28–days, 90–days). With this 
time horizon no discounting of costs and effects will be performed.  
9.4.2 Measurements 
The prospective cost evaluation will primarily focus on health care utilization (direct 
medical costs). The direct medical costs include the costs of all procedures and units 
associated with the ventilation strategies (e.g. fluids, vasopressors, sedatives, and 
ventilator days, ICU and hospital days). Health care utilization will be extracted from 
the hospital information system, hospital databases (e.g., the National Intensive Care 
Evalution (NICE) score, see www.stichting–nice.nl), case record forms (CRFs), 
financial reports, and patient files. Health service resource use and costs of both 
ventilation strategies will be measured from a health service and (if relevant) societal 
perspective. Protocol driven costs will be excluded.  
9.4.3 Unit costs 
Costs are defined as the volumes of used resources multiplied by calculated unit 
prices. For the evaluation of health care utilization standard prices published in the 

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current Dutch costing guidelines and market prices will be used. Standard guideline 
prices will be used (e.g., diagnostic interventions, hospital admissions).51 
9.4.4. Statistical analysis of Cost–effectiveness 
As most volumes of resource use follow a skewed distribution, differences between 
the two ventilation strategies will be statistically evaluated with bias–corrected 
bootstrap analysis.52 Incremental cost–effectiveness ratio will be calculated with the 
registered TISS/NAS–score as performance and effect parameter. The economic 
analysis will be expanded with a scenario–analysis to extrapolate the consequence of 
implementation and actual performance of the ventilation strategy with ‘restricted 
PEEP’ in the target population. The validity of the developed scenarios will be explored 
in a sensitivity analysis changing cost estimates and probabilities. 
9.5 Budget Impact Analysis (BIA) 
A budget impact analysis (BIA) will be designed and executed according to the ISPOR 
guidelines.53,54 The BIA will evaluate the nationwide economic/financial consequences 
of the adoption of treating non–ARDS patients at the ICU with ventilation with the 
lowest possible PEEP level or ventilation with the currently practiced PEEP level in the 
future. The analysis will be based on the decrease in ICU costs (e.g. ventilator–free 
days and alive at day 28) as estimated during the study. Registered data will be used, 
reflecting the size and characteristics of the eligible population in the Netherlands, the 
current and the new treatment mix, the effectiveness of ventilation with the currently 
practiced PEEP level and resource use and costs for the applied strategies and related 
side–effects. The BIA will be conducted from the perspective of the health care 
providers. When relevant, budget impact analysis is generated as a series of scenario 
analysis. 
Additional sensitivity analysis will be performed on the price of the intervention 
and the diffusion rate from the hospital perspective. 
 
 

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10. ETHICAL CONSIDERATIONS 
10.1 Regulation statement 
This trial will be conducted according to the principles of the Declaration of Helsinki as 
stated in the current version of Fortaleza, Brazil, 2013 and in accordance with the 
Medical Research Involving Human Subjects Act (WMO). 
10.2 Recruitment and consent 
10.2.1 Deferred consent 
For this trial we ask for deferred consent and we appeal to the emergency procedure 
for consent in medical research as stated in article 6, paragraph 4 of the WMO, as in 
a presently running trial of ventilation in a similar patient cohort, the ‘protective 
ventilation in patients not fulfilling the consensus definition for moderate or severe 
ARDS at start of ventilation – PReVENT, a randomized controlled trial (METC 
2014_075)58, for reasons as explained below. 
In patients admitted for ventilatory support to the ICU mechanical ventilation is 
needed urgently – consequently, mechanical ventilation starts right at ICU admission, 
or very short thereafter. The injurious effects of ventilation, however, could harm the 
lungs within hours and as such affect patient outcomes (see Text box 3 – Ventilation 
has the potential to harm the lungs – even after a short period of ventilation). For 
this reason, we consider it of utmost importance to set the ventilator according to the 
strategies of interest as soon as possible (i.e., within 1 hour after ICU admission, if 
ventilation started before admission), or within 1 hour after intubation and start of 
ventilation, if ventilation started after admission) – not doing so would largely reduce 
validity of this trial. 
Patients admitted for ventilatory support to the ICU are, without exception, 
incompetent to give informed consent. Persons who may take the role of legal 
representative in accordance with the WGBO are: a predefined representative, 
husband or wife, registered partner or other life partner, a parent or child, brother or 
sister, and incidentally a curator appointed the judge. However, obtaining informed 
consent from a legal representative in this situation usually takes much time, even by 
an experienced research team (see Textbox 4 – Experiences with deferred consent 
in critically ill patients). Reasons include the absence of a legal representative at 
time of intubation and start of ventilation, and early after admission to the ICU the legal 

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representatives are far more concerned about the wellbeing of the patient then 
participation in a trial.55,56 
For these reasons, we opt for using deferred consent, where informed consent 
from a legal representative must be obtained as soon as possible, but always within 
48 hours after randomization. If informed consent is not obtained, or if a legal 
representative denies participation within the time window of 48 hours, the patient is 
excluded and data will no longer be used. Thenceforth the patient is ventilated 
according to the policy of the attending physician. 
 
 
Textbox 3 - Ventilation has the potential to harm the lungs – even after a short 
period of ventilation 
Ventilation can harm the lungs, even after a short period of ventilation. If a patient, 
in the proposed trial, is already ventilated for several hours, injurious effects of 
ventilation could already be in place, largely reducing validity of the trial outcomes. 
From experimental animal studies we know that mechanical ventilation can cause 
effects within hours of ventilation with a high PEEP level.57 These findings are in line 
with results from clinical studies, showing ventilator-related effects after relative 
short periods of ventilation, e.g. after ventilation during general anesthesia for 
surgery.58 A recent randomized controlled trial of patients undergoing cardiac 
surgery with hypoxemia, comparing a ventilation strategy including a PEEP level of 
8 cm H2O with a ventilation strategy with a PEEP level of 13 cm H2O, showed an 
important effect of mechanical ventilation on the incidence of postoperative 
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10.2.2 Ethical aspects 
We can underpin the idea of ‘clinical equipoise’.60 Ventilation strategies with lower 
PEEP levels (sometimes even no PEEP) and higher PEEP levels have been used over 
the last decades in patients without ARDS, and we actually do not know what the best 
PEEP level in these patients is. A recent observational study in ventilation practice in 
Textbox 4 – Experiences with deferred consent in critically ill patients 
Most critically ill patients who need ventilation cannot be approached for informed 
consent for a study at ICU admission. Indeed, those patients are usually in severe 
respiratory distress, sedated or in coma. A prospective observational study on 
study recruitment practices in critically ill patients performed by a respected and 
experienced research group in Canada showed that the time from recognizing 
study eligibility to obtaining informed consent by a legal representative was as high 
as 12 hours, even while time from recognition to the first contact with a legal 
representative was as short as 2 hours.55 
The experience of ICU patients enrolled under deferred consent is mainly 
positive. To investigate contentment of patients that were included using deferred 
consent, a questionnaire was designed for – and distributed under the participants 
of the large NICE–SUGAR trial56, a trial compared a strict blood glucose control 
strategy with one that accepts higher blood glucose levels.57 Of the responders 
(79% of all participants), a large majority (96%) said to have granted consent if 
they would have been asked. A large majority (93%) mentioned they were happy 
with the decision made by the representative at the moment they were incapable 
of giving informed consent.57 
This is in line with our personal experience from the PReVENT trial (METC 
2014_075),58 a currently ongoing RCT in ventilated ICU patients without ARDS in 
The Netherlands, a study that compares two other ventilation strategies. From the 
PReVENT study we learned that it is very well possible to inform legal 
representatives about the trial within 24 hours. However due to longer travel 
distances for some of the legal representatives, obtaining written informed consent 
was sometimes not possible within the 24 hours: in as many as 19 out of 174 
patients (11%) this was a reason for exclusion of the patient. Interestingly, 
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ICU patients shows that a median PEEP level of 8 cm H2O is used in patients without 
ARDS in the Netherlands, and a medium level of 6 cm H2O is used in the European 
cohort.33 
10.2.3 No deferred consent in patients who die before obtaining informed  
consent 
In case a patient dies before informed consent could be obtained from the legal 
representative, we propose to use the data and inform the legal representative about 
the research without obtaining informed consent. This in in line with the advice from 
Jansen and colleagues regarding ethical validity and practical feasibility of deferred 
proxy consent in emergency critical care research and in line with the advice of the 
Central Committee on Research Involving Humans (CCMO, the Dutch national Ethics 
Committee) in these circumstances in the early lactate–directed therapy in the ICU.56,61 
The CCMO judged that the situation when a patient dies before consent could 
be obtained is comparable with the situation in which the research project has already 
finished at the time deferred consent can be obtained. They concluded that the legal 
representative should be notified about the study, but that seeking consent was not 
useful anymore due to the lack of consequences. The representation of the patient by 
a legal representative ends when the patient dies. In the Dutch law, the consent of the 
patient or his/her relative primarily relates to the participation in the study and not to 
using the data collected in the study. 56 
10.2.4 Conclusion deferred consent 
Critically ill patients in need of ventilation are, without exception, incapable to give 
informed consent at the moment of ICU admission.  Obtaining informed consent from 
a legal representative takes too much time to allow timely start of the ventilation 
strategies to be compared in this trial. Timely start is essential due to the risk of the 
injurious effects on the lungs even after a short period of ventilation not following 
protocol and thereby reducing the validity of the trial. Both ventilation strategies to be 
compared in this trial have been used in the last decades, and we do not know what 
the best PEEP level is. 
 
 

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10.3 Benefits and risks assessment, group relatedness 
Burden and risks of the ventilation strategies are uncertain. Ventilation with the lowest 
possible PEEP level could increase the risk of atelectasis and also the risk of potentially 
dangerous hypoxemia. Ventilation with the PEEP level currently practiced could 
increase the amount of overdistended lung tissue and increase hemodynamic 
compromise. Both ventilation strategies are currently used; there is no additional risk 
for patients enrolled in this study compared to current practice. 
We specifically chose not to exclude incompetent patients for two reasons. First, 
critically ill patients needing mechanical ventilation should be considered incompetent 
due to their needs for continuous sedation. Second, the strategies to be compared in 
this study are to be used in critically ill, intubated and ventilated patients. These 
conditions are not present in patients who are not suffering from a critical disease. We 
therefore consider it impossible not to include these patients in a study comparing 
strategies for mechanical ventilation.  
10.4 Compensation of injury 
The sponsor/investigator has a liability insurance, which is in accordance with article 7 
subsection 6 of the WMO. As this study compares two ventilation strategies used for 
standard care an exception from the requirement for insurance to cover for damage to 
research subjects through injury or death caused by the study is applicable. 
 
 

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11. ADMINISTRATIVE ASPECTS, MONITORING AND PUBLICATION 
11.1 Handling and storage of data and documents 
All patients will be addressed to the inventions with a random patient identification 
code. The codebook will be stored digitally and in paper. The paper version will be 
stored behind a lock and the digital form will be encrypted with a double password. All 
data will be stored for the length of the study and for 15 years afterwards. All handling 
of personal date will comply with the Dutch Personal Data Protection Act. 
11.2 Monitoring and Quality Assurance 
Queries on the database will be done by a statistician and analyzed by the monitor to 
signalize early aberrant patterns, trends, issues with consistency of credibility and 
other anomalies. 
On site monitoring will compromise controlling presence and completeness of the 
research dossier and the informed consent forms, source data checks will be 
performed as described in the monitoring plan. Every participating center will be visited 
after the inclusion of the first ten patients and thereafter at least once every year. A 
monitoring plan is being developed. 
11.3 Amendments 
Amendments are changes made to the research after a favorable opinion by the 
accredited METC has been given. All substantial amendments will be notified to the 
METC and to the competent authority. Non–substantial amendments (typing errors 
and administrative changes) will not be notified to accredited METC and the competent 
authority, but will be recorded and filed by the sponsor. 
11.4 Annual progress report 
The investigator will submit a summary of the progress of the trial to the accredited 
METC once a year. Information will be provided on the date of inclusion of the first 
subject, numbers of subjects included and numbers of subjects that have completed 
the trial, unexpected problems and amendments 
11.5 End of study report 
The investigator will notify the accredited METC of the end of the study within a period 
of 8 weeks. The end of the study is defined as the 90th day after the last patients 
inclusion in the study. In case the study is ended prematurely, the investigator will notify 
the accredited METC within 15 days, including the reasons for the premature 
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submit a final study report with the results of the study, including any 
publications/abstracts of the study, to the accredited METC. 
11.6 Public disclosure and publication policy 
The study protocol will be registered before inclusion of the first patient on 
Clinicaltrials.gov. The results of the study will find their way into (inter–)national 
scientific journals and guidelines. We will submit analyses to scientific journals in the 
field of intensive care medicine as well as anesthesiology, since both ICU physicians 
and anesthesiologists apply ventilation in the ICU setting. 

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12. PUBLICATION POLICY 
The PROVENet policy will be followed for publication. The intention is to publish the 
paper by the PROVE Network investigators. This means that there will be no names 
of individual researchers above a publication. The Principal Investigator is mentioned 
as the contact person, the members of the Steering Committee, the Writing Committee, 
and all local investigators of participating centers are summarized at the end of a 
manuscript or in the appendix depending on the journal policy. In this way 
http://www.ncbi.nlm.nih.gov/pubmed/  
 can link the names of all investigators to a publication. If a journal does not accept 
this, another approach will be discussed within the Steering Committee, and an 
explanation and conclusion will be posted on the website of the project. 
 
From each participating center in the RELAx trial one local investigator per 
participating center will be on the authors list for publication. When a participating 
center includes more than the anticipated 82 patients per center, a second local 
investigator will be added to the authors list for publication. In case a participating 
center includes more than 164 patients, a third local investigator will be added to the 
authors list for publication. 
 
 

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practice of ventilation, and clinical outcome in patients at risk of acute 
respiratory distress syndrome in intensive care units from 16 countries 
(PRoVENT): an international, multicentre, prospective study. Lancet Respir 
Med. 2016;4(11):882-893. doi:10.1016/S2213-2600(16)30305-8. 
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doi:10.1164/rccm.200912-1918OC. 
 
 
 
 

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APPENDIX I 
Table 1. The Berlin definition for ARDS 36,37 
Timing 
Within 1 week of a known clinical insult, or new/worsening respiratory symptoms 
Chest 
imaging* 
Bilateral opacities—not fully explained by effusions, lobar/lung collapse, or nodules 
Origin of 
edema 
Respiratory failure not fully explained by cardiac failure or fluid overload; need objective 
assessment (e.g., echocardiography) to exclude hydrostatic edema if no risk factor present 
Oxygenation 
Mild 
Moderate 
Severe 
200 < PaO2/ FiO2 ≤ 300 
mmHg 
100 < PaO2/ FiO2 ≤ 200 
mmHg 
PaO2/ FiO2 ≤100 mmHg 
26.7 < PaO2/ FiO2 ≤ 40 kPa 
with PEEP ≥ 5 cm H2O or 
CPAP ≥ 5 cm H2O 
13.3 < PaO2/ FiO2 ≤ 26.7 
kPa with PEEP ≥ 5 cm H2O 
PaO2/ FiO2 ≤ 13.3 kPa with 
PEEP ≥ 5 cm H2O 
*Chest radiograph or CT scan; ** If altitude higher than 1000 m, correction factor should be made as follows: 
PaO2/ FiO2 9 (barometric pressure/760) 
Abbreviations: ARDS, acute respiratory distress syndrome; PaO2, partial pressure of arterial oxygen; FiO2, 
fraction of inspired oxygen; PEEP, positive end–expiratory pressure; CPAP, continuous positive airway. 
 
DEFINITIONS 
 APACHE (Acute Physiology and Chronic Health Evaluation) II: a point score 
ranging from 0–71, calculated from 12 measurements (age, temperature 
(rectal), mean arterial pressure, pH, heart rate, respiratory rate, sodium 
(serum), potassium (serum), creatinine, hematocrit, white blood cell count, 
GCS) higher scores correspond to more severe disease and higher risk of 
death   
 MRC (Medical Research Council): grades strength in functional muscle groups 
in each extremity, ranging 0–5, a score of 5 corresponds to normal – healthy 
strength 
 Pneumonia: new or progressive radiographic infiltrate plus at least two of the 
following: fever tympanic temperature > 38,5, leukocytosis or leucopenia 
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 Pneumothorax: air in the pleural space with no vascular bed surrounding the 
visceral pleura on chest radiograph or other kind of imaging suitable for 
diagnosis severe atelectasis 
 Recruitment maneuver: increase of inspiratory pressure or the level of PEEP 
for at least 40 seconds 
 SAPS (Simplified Acute Physiology Score) II: point score ranging from 0–163, 
as APACHE   
 Severe atelectasis: at least complete lobar atelectasis of a lung on chest 
radiograph or other kind of imaging suitable for diagnosis severe atelectasis 
 Severe hypoxemia: SpO2 < 88% or < PaO2 7.3 kPa more than 5 minutes or a 
rise of the oxygen fraction > 60% for more than 5 minutes related to a 
hypoxemic event  
 
 

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APPENDIX II 
SCHEME FOR UNASSISTED VENTILATION WITH TRACHEOSTOMY 
The following suggested scheme can be used for unassisted ventilation with a 
tracheostomy, but should be individualized in every patient: 
1. Unassisted ventilation for 30 minutes, three times per day 
2. Unassisted ventilation for 1 hour, three times per day 
3. Unassisted ventilation for 2 hours, three times per day   
4. Unassisted ventilation for 4 hours, three times per day   
5. Unassisted ventilation for 6 hours, two times per day   
6. Unassisted ventilation for 18 hours 
7. Unassisted ventilation for 24 hours 
 
 
 

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APPENDIX III 
PATIENTS EXAMPLES FOR CLARIFICATION VENTILATION WITH ‘RESTRICTED 
PEEP’–ARM  
 
 
 
 
Patient A is intubated and ventilated due to decreased level of consciousness as a 
result of intoxication with presumed GHB. Patient A fulfills the inclusion criteria and is 
included in the RELAx study and randomized to the ‘restricted PEEP’–arm. The 
ventilation is started with a PEEP level of 5 cm H2O and FiO2 of 0.4, the saturation is 
stable and remains SpO2 > 94%. Following the flowchart, the oxygenation target range 
is reached and stable, hence the PEEP level can be ‘down-titrated’ with increments of 
1 cm H2O with reassessment of the saturation every 15 minutes following each 
adjustment of the PEEP level. The PEEP level is successfully ‘down-titrated’ to a PEEP 
level of 0 cm H2O with a SpO2 93%. Since the oxygenation target range is reached and 
stable, the attending physician is able to decrease the FiO2 level from 0.4 to 0.21.  
 
Patient B is a trauma patient with a flail chest, and is intubated and ventilated 
due to respiratory insufficiency. Patient B is a candidate for the RELAx study and is 
randomized to the ‘restricted PEEP’–arm. Ventilation is started with a PEEP level of 5 
cm H2O, soon the oxygenation target range is reached and the PEEP level is 
successfully ‘down-titrated’ to 0 cm H2O with a FiO2 of 0.3 while maintaining the 
oxygenation target (SpO2 > 92%). The admission is complicated by a ventilator 
acquired pneumonia (VAP) and purulent secretion is noticed, treatment with antibiotics 
is started. On the fifth day of admission, suddenly the saturation drops to SpO2 88%. 
The FiO2 is increased to 0.6 and the PEEP level was set back at 5 cm H2O. Since lots 
of purulent secretion was removed earlier that day, a mucus plug is considered and 
the attending physician performs a recruitment maneuver successfully with 
improvement of oxygenation (SpO2 93%). During reassessment, the saturation 
remains stable and within the oxygenation target range, therefore the PEEP level can 
be ‘down-titrated’ again. 

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Patient C is admitted due to a respiratory infection. Patient C is intubated due to 
respiratory insufficiency which developed the same day and is admitted to the ICU. 
Patient C is eligible for the RELAx study and is randomized to the ‘restricted PEEP’–
arm. Ventilation is started with a PEEP level of 5 cm H2O and a FiO2 of 0.5, the saturation 
is SpO2 92%. Attempts for ‘down-titration’ of the PEEP level are unsuccessful and 
therefore the PEEP level and the FiO2 remains unchanged. However, that afternoon the 
SpO2 drops to 88%, the FiO2 is increased to 0.6 and the PEEP level of 5 cm H2O is 
maintained. During reassessment, the oxygenation target range is not reached and 
consequently adjustments are made with increasing the FiO2 and the PEEP level further, 
until 10 cm H2O and 0.8.  
A chest radiograph is obtained with the appearance of bilateral infiltrates. Patient C is 
clinically diagnosed with ARDS, since the respiratory failure cannot be explained by 
cardiac failure or fluid overload. Ventilation is continued according to the existing ARDS 
guidelines. 

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APPENDIX IV 
Substudy – ‘RELAxECHO’ 
Background 
Cardiac function, in particularly of the right ventricle, depends on intrathoracic 
pressures[1,2]. Use of positive end–expiratory pressure (PEEP) could increase right 
atrial pressure, pulmonary vascular resistances and right ventricular afterload[3-5] . 
The net effect of PEEP may be a decrease in right ventricle (RV) volume and output, 
with no changes in ejection fraction [3]. One small study showed a negative effect of 
high PEEP on right ventricular strain[6], a surrogate measure of contractility. It is 
uncertain whether low PEEP has an independent effect on right ventricle myocardial 
strain. The myocardial performance index (MPI) is regarded as an easy and 
reproducible echocardiographic parameter of both systolic and diastolic function. The 
MPI is relatively independent of changes in loading conditions in various clinical 
settings [8-11]. The RELAx study provides a unique opportunity to study cardiac 
performance and especially the performance of the right ventricle during varying levels 
of PEEP (between 0 and 8 cm H2O) in patients with uninjured lungs. 
Aim 
The aim of RELAxECHO, a substudy of the RELAx study, is to assess and compare 
changes in cardiac function as measured by transthoracic echocardiography (TTE) in 
the two study groups. 
Hypothesis 
We hypothesize that ventilation with liberal PEEP decreases right ventricular function 
after 24-48 hours of mechanical ventilation. 
Endpoint 
The primary endpoint of this sub study is the myocardial performance index of the right 
ventricle in the first 24-48 hours of mechanical ventilation. 
In– and exclusion criteria 
Inclusion criteria: 
 Admitted to the ICU of the Academic Medical Center 
 Enrolled in the RELAx study 
Exclusion criteria: 

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 Ventilation with PEEP > 2 cm H2O in the ‘restricted PEEP’–arm and ventilation with 
PEEP < 7 cm H2O in the ‘liberal PEEP’–arm 
 Refractory circulatory instability requiring > 5 μg/kg/min dopamine or dobutamine, 
> 1 mg/hour milrinone, or norepinephrine dose of > 0.4 μg/kg/min 
 Documented poor left ventricular function (e.g. left ventricular ejection fraction ≤ 
30%) 
Original sample size calculation 
We estimated 28 patients in each study group to achieve a power of 80%, with a two–
sided significance level of 0.05, to detect a 0.06 difference in change in myocardial 
performance index between ventilation with restricted PEEP (defined as a PEEP ≤ 2 
cm H2O) and ventilation with liberal PEEP (defined as a PEEP ≥ 7 cm H2O), assuming 
a standard deviation of 0.08. The sample size is increased by 20% to correct for 
dropouts (i.e., if myocardial performance index cannot be determined from the TTE 
due to poor echogenicity), meaning that a total of 68 patients are required. The decision 
about the sample size is based upon the consideration that the quantity of PEEP has 
an effect on right ventricular function [6]. Differences in right ventricular function are 
expressed in the myocardial performance index, which is a parameter known to be 
relatively load–independent. 
Sample size re-calculation 
Based on the results of a recent study in a similar patient cohort, showing a much 
larger decrease of 0.23 in myocardial performance index with lower tidal volume 
reduction, [7] the sample size was recalculated on 12 November 2019 as follows. With 
a still conservative effect size on MPI of the right ventricle of 0.12 (an effect size half 
the size of the previous study [7]), and a mean MPI of the right ventricle of 0.41 and a 
standard deviation of 0.13, we need 18 patients in each study group to detect a 
difference of 0.12 in MPI of the right ventricle with PEEP reduction with 80% power 
with a two–sided significance level of 0.05. The sample size is increased by 20% to 
correct for dropouts, meaning that a total of 44 patients (22 per group) are required. 
Methods 
Cardiac ultrasound is performed within 24 to 48 hours after enrollment in the RELAx 
study. The cardiac echocardiography will be performed by trained physicians under 
supervision of cardio-intensivists, will perform the echocardiography, using the GE 
Healthcare Vivid 9 ultrasound machine with a 2–5 MHz sector probe. Traditional 

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echocardiographic measures, tissue Doppler imaging (TDI) and speckle tracking 
echocardiography (STE) parameters will be collected online and with post-acquisition 
offline analysis[12]. Images of the ventricles are analyzed offline for the myocardial 
performance index, strain and strain rate and diastolic parameters. Ultrasound clips 
will be saved for further offline STE analysis and quality control. Measurements will be 
performed after at least 5 minutes of stable mean arterial pressure. Bidimensional and 
Doppler measurements will be made in accordance with current recommendations of 
the American Society of Echocardiography[13]. 
Statistical analysis 
Normally distributed variables are expressed by their mean and standard deviation; 
non–normally distributed variables are expressed by their medians and interquartile 
ranges. Categorical variables will be expressed as n (%). To test groups of continuous 
normally distributed variables, Student’s t–test will be used. Likewise if continuous data 
is not normally distributed the Mann–Whitney U test will be used. Categorical variables 
will be compared with the Chi–square test or Fisher’s exact tests or when appropriate 
as relative risks. Statistical significance is considered to be at a p–value of 0.05. Where 
appropriate, statistical uncertainty will be expressed by 95% confidence levels. 
Analysis will be performed with R (www.r-project.org). 
Informed consent 
Deferred informed consent from a legal representative is obtained as soon as possibly 
for this sub study as part of the parent study RELAx. In case a patient is awake and 
adequate informed consent will be obtained from the patient. 
References 
1. Luecke T, Pelosi P. Clinical review: Positive end-expiratory pressure and cardiac 
output. Crit Care. BioMed Central; 2005;9:607–21.  
2. Luecke T, Roth H, Joachim A, Herrmann P, Deventer B, Weisser G, et al. Effects 
of end-inspiratory and end-expiratory pressures on alveolar recruitment and 
derecruitment in saline-washout-induced lung injury -- a computed tomography study. 
Acta Anaesthesiol Scand. 2004;48:82–92.  
3. Pinsky MR. My paper 20 years later: Effect of positive end-expiratory pressure on 
right ventricular function in humans. Intensive Care Med. Springer Berlin Heidelberg; 
2014;40:935–41.  
4. Tyberg JV, Taichman GC, Smith ER, Douglas NW, Smiseth OA, Keon WJ. The 
relationship between pericardial pressure and right atrial pressure: an intraoperative 
study. Circulation. American Heart Association, Inc; 1986;73:428–32.  

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5. Biondi JW, Schulman DS, Soufer R, Matthay RA, Hines RL, Kay HR, et al. The 
effect of incremental positive end-expiratory pressure on right ventricular 
hemodynamics and ejection fraction. Anesth. Analg. 1988;67:144–51.  
6. Franchi F, Faltoni A, Cameli M, Muzzi L, Lisi M, Cubattoli L, et al. Influence of 
positive end-expiratory pressure on myocardial strain assessed by speckle tracking 
echocardiography in mechanically ventilated patients. Biomed Res Int. Hindawi; 
2013;2013:918548–8. 
7. Cherpanath TGV, Simonis FD, Bouma BJ, de Bruin-Bon RH, Determann RM, 
Juffermans NP, et al. Myocardial function during low versus intermediate tidal 
volumes ventilation in patients without ARDS. Anesthesiology; 2019; in press. 
8. Tei C. New non-invasive index for combined systolic and diastolic ventricular 
function. J Cardiol. 1995;26:135–6.  
9. Yeo TC, Dujardin KS, Tei C, Mahoney DW, McGoon MD, Seward JB. Value of a 
Doppler-derived index combining systolic and diastolic time intervals in predicting 
outcome in primary pulmonary hypertension. Am. J. Cardiol. 1998;81:1157–61.  
10. ARNLOV J, INGELSSON E, RISERUS U, ANDREN B, LIND L. Myocardial 
performance index, a Doppler-derived index of global left ventricular function, 
predicts congestive heart failure in elderly men. European Heart Journal. 
2004;25:2220–5.  
11. Kato M, Dote K, Sasaki S, Goto K, Takemoto H, Habara S, et al. Myocardial 
performance index for assessment of left ventricular outcome in successfully 
recanalised anterior myocardial infarction. Heart. BMJ Publishing Group Ltd; 
2005;91:583–8.  
12. Mondillo S, Galderisi M, Mele D, Cameli M, Lomoriello VS, Zacà V, et al. 
Speckle-tracking echocardiography: a new technique for assessing myocardial 
function. J Ultrasound Med. 2011;30:71–83.  
13. Lang RM, Bierig M, Devereux RB, Flachskampf FA, Foster E, Pellikka PA, et al. 
Recommendations for chamber quantification: a report from the American Society of 
Echocardiography's Guidelines and Standards Committee and the Chamber 
Quantification Writing Group, developed in conjunction with the European 
Association of Echocardiography, a branch of the European Society of Cardiology. J 
Am Soc Echocardiogr. 2005. pp. 1440–63.  
 
 
 
 
 
 

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APPENDIX V 
Substudy – ‘RELAxLUS’ 
Background 
Ventilation with low PEEP may increase the risk of atelectasis in critically ill patients 
receiving invasive ventilation, as has been shown before in patients undergoing 
intraoperative ventilation (1, 2). Lung ultrasound (LUS) is a non–invasive relatively 
simple bedside technique used to semi–quantify changes in lung aeration in ventilated 
patients (3), and very capable to detect atelectasis (4). 
Aim 
The aim of RELAxLUS, a substudy of the RELAx study, is to assess and compare 
changes in pulmonary aeration and presence of atelectases as detected by LUS in the 
two study groups. 
Hypothesis 
We hypothesize that ventilation with restricted PEEP results in a decrease in lung 
aeration and an increase in atelectases. 
Endpoint 
The primary endpoint of this sub study is the change in lung ultrasound aeration score 
in the first 48 hours of invasive ventilation. 
In– and exclusion criteria 
Inclusion criteria: 
 Admitted to the ICU of the Academic Medical Center 
 Enrolled in the RELAx study 
Exclusion criteria: 
 Evidence of cardiac failure or fluid overload, based on an objective assessment 
such as echocardiography in the medical record and/or on judgment of the treating 
physician 
Methods 
LUS is performed at three predefined time points: within 12 hours after enrolment in 
the RELAx study (this LUS examination is standard of care in patients that are 
expected to need invasive ventilation > 24 hours), between 24 to 48 hours after 
enrolment and within the first 24 hours after extubation. Experienced and trained 
physician will perform LUS examinations, using a 2–5 MHz convex probe. Each 

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hemithorax is divided into six areas: the anterior, lateral and posterior areas, each 
divided in upper and lower quadrants, using the parasternal line, the anterior axillary 
line, the posterior axillary line and the paravertebral line as borders (Figure 1). The 12 
regions are examined and a semi–quantitative score is calculated to estimate lung 
aeration at each time point, and documented in a case report form (see Table 1). 
Additional sonographic signs previously described for atelectasis will be reported when 
present for each of the 12 lung regions examined. These include the absence or 
reduction in lung sliding, the presence of subpleural consolidations and presence of 
static air bronchograms in consolidated areas (5). 
 
 
 
 
 
 
 
 
Figure 1. Six zones are scanned per hemithorax. 
 
Table 1. LUS aeration score 
Pattern  Score View 
Interpretation 
A 
0 
Only A lines visible or isolated ≤2 
B–lines  
Normal lung aeration 
B1 
1 
Multiple well-defined either 
regularly spaced or irregularly 
spaced B–lines 
Moderate loss of lung 
aeration 
B2 
2 
Multiple coalescent B–lines 
Severe loss of lung 
aeration 
C 
3 
Hypoechoic or tissue–like area 
Consolidated lung tissue 
 
Informed consent 
Written informed consent is obtained for the two extra LUS examinations as part of the 
informed consent for the parent study (RELAx), i.e., the one between 24 and 48 hours 
after enrolment, and the one within the first 24 hours after extubation, as the first LUS 
examination is standard of care in these patients. 
References 
1.  
Martin JB, Garbee D, Bonanno L: Effectiveness of positive end-expiratory 
pressure, decreased fraction of inspired oxygen and vital capacity recruitment 
maneuver in the prevention of pulmonary atelectasis in patients undergoing 
general anesthesia: a systematic review. JBI Database Syst Rev Implement 

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Reports 2015; 13:211 
2.  
Dyhr T, Laursen N, Larsson A: Effects of lung recruitment maneuver and positive 
end-expiratory pressure on lung volume, respiratory mechanics and alveolar gas 
mixing in patients ventilated after cardiac surgery. Acta Anaesthesiol Scand 
2002; 46:717–25 
3.  
Bouhemad B, Mongodi S, Via G, et al.: Ultrasound for “Lung Monitoring” of 
Ventilated Patients. Anesthesiology 2015; 122:437–447 
4.  
Monastesse A, Girard F, Massicotte N, et al.: Lung Ultrasonography for the 
Assessment of Perioperative Atelectasis: A Pilot Feasibility Study. Anesth Analg 
2017; 124:494–504 
5.  
Acosta CM, Maidana GA, Jacovitti D, et al.: Accuracy of transthoracic lung 
ultrasound for diagnosing 
anesthesia-induced 
atelectasis in 
children. 
Anesthesiology 2014; 120:1370–1379 
 
 
 

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APPENDIX VI 
Substudy – ‘RELAxBiomarkers’ 
Background 
Mechanical ventilation has a strong potential to inflame and damage lung tissue. 
Plasma level of several markers of inflammation and lung damage, including tumor 
necrosis factor (TNF)–alpha, Interleukin (IL)–6 and IL–8, the soluble form of the 
Receptor for Advanced Glycation End–products (sRAGE), Surfactant Protein (SP)–D, 
Clara Cell protein (CC)–16 and Krebs von den Lungen 6 (KL6), have been shown to 
rise in response to intraoperative ventilation and depending on ventilator settings used 
[1]2. Plasma levels of these biomarkers also rise in response to mechanical ventilation 
using large tidal volumes [2]. The RELAx trial offers the unique opportunity to study the 
dependence of plasma levels of biomarkers of inflammation and lung damage on the 
level of PEEP used during the first week of mechanical ventilation in patients with 
uninjured lungs. 
Aim 
The aim of RELAxBiomarkers, a substudy of RELAx, is to describe and compare 
changes in plasma levels of biomarkers of inflammation and pulmonary injury. 
Hypothesis 
We hypothesize that ventilation with liberal PEEP, compared to ventilation with 
restricted PEEP, increases plasma levels of biomarkers of inflammation and 
pulmonary injury. 
Endpoints 
The endpoint of this substudy is the difference in plasma levels of biomarkers of 
inflammation and pulmonary injury between the two study groups. 
In- and exclusion criteria 
Inclusion criteria 
 Admitted to the ICU of the Academic Medical Center 
 Enrolled in the RELAx study 
Exclusion criteria 
 Receiving immunosuppressive medication 
Methods 
Blood sampling and handling 

NL60402.018.17 
 
 
RELAx version 6.2, 06–12–2019 
 
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Left–over blood from arterial blood samples used for arterial blood gas analysis, taken 
as part of standard of care in the morning, will be collected within 12 to 16 hours after 
enrolment in the RELAx study, and thereafter till day 7 or until ICU discharge, 
whichever comes first. 
Blood samples are centrifuged at 2,000 rpm for 15 minutes. Supernatant is collected 
and stored at –80OC until batchwise analysis, using customized Luminex kits for 
measurements of biomarkers of inflammation and lung injury, including TNF–alpha, 
IL–6, IL–8, sRAGE, SP–D, CC–16, and KL6. 
Statistical analysis 
Variables are expressed in mean plus standard deviation, or medians plus interquartile 
ranges where appropriate. Categorical variables are expressed as proportions. 
Student’s t and Mann–Whitney U test are used depending on distribution of data. 
Categorical variables will be compared with the Chi–square test or Fisher’s exact tests 
or when appropriate as relative risks. Statistical significance is considered to be at a 
p–value of 0.05. Where appropriate, statistical uncertainty will be expressed by 95% 
confidence levels. All analysis will be performed with R (www.r-project.org). 
Informed consent 
Written informed consent for the use left–over blood from arterial blood samples is 
asked as part of the informed consent for the parent study, RELAx. 
References 
1. Serpa Neto A, Campos PPZA, Hemmes SNT, Bos LD, Bluth T, Ferner M, et al. 
Kinetics of plasma biomarkers of inflammation and lung injury in surgical patients with 
or without postoperative pulmonary complications. Eur J Anaesthesiol. 2017;34:229–
38.  
2. Determann RM, Royakkers A, Wolthuis EK, Vlaar AP, Choi G, Paulus F, et al. 
Ventilation with lower tidal volumes as compared with conventional tidal volumes for 
patients without acute lung injury: a preventive randomized controlled trial. Crit Care. 
BioMed Central; 2010;14:R1.