Lung Recruitment in Obese Patients with Acute Respiratory Distress Syndrome
Authors: Fumagalli Jacopo , Santiago Roberta R. S. , Teggia Droghi Maddalena , Zhang Changsheng , Fintelmann Florian J. , Troschel Fabian M. , Morais Caio C. A. , Amato Marcelo B. P. , Kacmarek Robert M. , Berra Lorenzo ,   on behalf of the Lung Rescue Team Investigators
Published: March 2019

Abstract

Editor’s Perspective

What We Already Know about This Topic
Obesity increases the propensity to atelectasis in acute respiratory distress syndrome, but the optimal approach to reversing this atelectasis is uncertain

What This Article Tells Us That Is New
A clinical crossover study comparing three approaches to titrate positive end-expiratory pressure (PEEP; according to a fixed table, according to end-expiratory esophageal pressure, and targeting the best compliance during a decremental PEEP trial) found that a recruitment maneuver followed by decremental PEEP minimized atelectasis and overdistension, and best restored compliance and oxygenation without causing hemodynamic impairment

Background
Obese patients are characterized by normal chest-wall elastance and high pleural pressure and have been excluded from trials assessing best strategies to set positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS). The authors hypothesized that severely obese patients with ARDS present with a high degree of lung collapse, reversible by titrated PEEP preceded by a lung recruitment maneuver.

Methods
Severely obese ARDS patients were enrolled in a physiologic crossover study evaluating the effects of three PEEP titration strategies applied in the following order: (1) PEEPARDSNET: the low PEEP/Fio
2 ARDSnet table; (2) PEEPINCREMENTAL: PEEP levels set to determine a positive end-expiratory transpulmonary pressure; and (3) PEEPDECREMENTAL: PEEP levels set to determine the lowest respiratory system elastance during a decremental PEEP trial following a recruitment maneuver on respiratory mechanics, regional lung collapse, and overdistension according to electrical impedance tomography and gas exchange.

Results
Fourteen patients underwent the study procedures. At PEEPARDSNET (13 ± 1 cm H2O) end-expiratory transpulmonary pressure was negative (−5 ± 5 cm H2O), lung elastance was 27 ± 12 cm H2O/L, and PaO2/Fio
2 was 194 ± 111 mmHg. Compared to PEEPARDSNET, at PEEPINCREMENTAL level (22 ± 3 cm H2O) lung volume increased (977 ± 708 ml), lung elastance decreased (23 ± 7 cm H2O/l), lung collapse decreased (18 ± 10%), and ventilation homogeneity increased thus rising oxygenation (251 ± 105 mmHg), despite higher overdistension levels (16 ± 12%), all values P < 0.05 versus PEEPARDSnet. Setting PEEP according to a PEEPDECREMENTAL trial after a recruitment maneuver (21 ± 4 cm H2O, P = 0.99 vs. PEEPINCREMENTAL) further lowered lung elastance (19 ± 6 cm H2O/l) and increased oxygenation (329 ± 82 mmHg) while reducing lung collapse (9 ± 2%) and overdistension (11 ± 2%), all values P < 0.05 versus PEEPARDSnet and PEEPINCREMENTAL. All patients were maintained on titrated PEEP levels up to 24 h without hemodynamic or ventilation related complications.

Conclusions
Among the PEEP titration strategies tested, setting PEEP according to a PEEPDECREMENTAL trial preceded by a recruitment maneuver obtained the best lung function by decreasing lung overdistension and collapse, restoring lung elastance, and oxygenation suggesting lung tissue recruitment.