Effect of PEEP on Lung Recruitment and Homogeneity Over Time in Moderate to Severe ARDS

Study Overview
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Brief Summary
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This study evaluates the effect of airway pressure release ventilation (APRV) on lung homogeneity and recruitment in patients with moderate to severe acute respiratory distress syndrome (ARDS). It will do this by comparing the homogeneity of ventilation and recruitment prior to a patient being ventilated on APRV, and at 30, 60 and 120 minutes after starting APRV.

Detailed Description
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Ventilator-induced lung injury (VILI) is a well-recognised problem of ventilation in patients with ARDS, and is currently treated with lung-protective ventilation, which limits tidal volumes and airway pressures by applying higher levels of positive-end expiratory pressure (PEEP). However, it is not known whether higher levels of PEEP increases recruitment and homogeneity of ventilation within the lungs. APRV is a mode of inverse ventilation, where high levels of PEEP are maintained with brief releases of pressure, and has been proposed as an appropriate method of ventilation in patients with ARDS. This study will assess homogeneity of ventilation and recruitment in 15 patients before APRV is started, and 30, 60 and 120 mins after commencing APRV. It will do this using Electrical Impedance Tomography (EIT), nitrogen wash in/wash out technique, and lung strain.

Official Title
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Estimation of Long Term PEEP Effect on Lung Homogeneity and Recruitment Using APRV Ventilation:Measurement of End Expiratory Lung Volume With Nitrogen Wash-out/wash-in Technique and End Expiratory Lung Impedance With EIT at Different Times.

Conditions
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ARDS, Critical Illness, Ventilator-Induced Lung Injury

Intervention / Treatment
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* Other: APRV


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Age ≥ 18 years and < 80 years Weight > 35 Kg and BMI < 40 Informed consent according to local regulations Hemoglobin ≥ 70 g/dl Haemodynamically stable > 4 hours Moderate to severe ARDS (PaO2/FIO2 < 26.6 kPa with positive end-expiratory pressure (PEEP) > 5 cmH2O) as per Berlin definition of ARDS Exclusion Criteria: Expected survival < 72 hours Suspected pregnancy (negative pregnancy test required for women of child-bearing potential) Open abdomen Documented or suspected raised intracranial pressure Active air leak (pneumothorax, pneumomediastinum, subcutaneous emphysema) Morbid obesity BMI > 40 Recent < 1 week cardiac or thoracic surgery Unstable thorax and sternum with paradoxical chest wall movement Severe Chronic Respiratory Disease (COPD) - GOLD 3 or 4 emphysema with bullae Severe smoking (> 40 pack-year history) Liver Failure: Child-Pugh Class C Massive ascites Lung fibrosis Severe cardiac disease (one of the following): New York Heart Association Class III or IV, acute coronary syndrome or persistent ventricular tachyarrhythmias Sickle cell disease

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 80 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Intervention/Treatment |
| --- |
|Other: APRV|Airway pressure release ventilation is a method of inverse ventilation, where high levels of positive end expiratory pressure are maintained to optimise oxygenation with brief releases of pressure to allow ventilation and release carbon dioxide. It is an approved and frequently used method of ventilation.|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| To compare lung homogeneity estimated with EIT upon commencing APRV (APRVpre) and after 30 - 60 - 120 min of APRV ventilation (APRV30, APRV60, APRV120) in patients with moderate to severe ARDS | EIT will be measured at time APRVpre during a low-flow maneuver consisting of a brief switch to PC ventilation: with a flow of 4 L/min, airway pressure will be gradually increased up to 30 cmH20 in order to see how the lung changes elastically minimising resistance. EIT will also be measured after 30 min (time APRV30), 60 min (time APRV60), 120 min (time APRV120) since APRV has started. | 30, 60 and 120 mins | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| To assess recruitment at the beginning and after the end of APRV ventilation in patients with moderate-severe ARDS. | To assess recruitment measuring change in end expiratory lung impedance (EELI) with EIT technique, and EELV with nitrogen wash-out/wash-in technique. | 2 hours | 
| To compare lung strain measured at APRVpre and after the end of APRV ventilation (APRVpost) in patients with moderate-severe ARDS | Strain will be calculated at time APRVpre using the strain formula (TV/EELV) | 2 hours | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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recruitment, lung homogeneity, airway pressure release ventilation