Individualized versus Fixed Positive End-expiratory Pressure for Intraoperative Mechanical Ventilation in Obese Patients: A Secondary Analysis
Authors: Simon Philipp , Girrbach Felix , Petroff David , Schliewe Nadja , Hempel Gunther , Lange Mirko , Bluth Thomas , Gama de Abreu Marcelo , Beda Alessandro , Schultz Marcus J. , Pelosi Paolo , Reske Andreas W. , Wrigge Hermann ,   for the PROBESE Investigators of the Protective Ventilation Network* and the Clinical Trial Network of the European Society of Anesthesiology
Published: April 2021

Background
General anesthesia may cause atelectasis and deterioration in oxygenation in obese patients. The authors hypothesized that individualized positive end-expiratory pressure (PEEP) improves intraoperative oxygenation and ventilation distribution compared to fixed PEEP.

Methods
This secondary analysis included all obese patients recruited at University Hospital of Leipzig from the multicenter Protective Intraoperative Ventilation with Higher versus Lower Levels of Positive End-Expiratory Pressure in Obese Patients (PROBESE) trial (n = 42) and likewise all obese patients from a local single-center trial (n = 54). Inclusion criteria for both trials were elective laparoscopic abdominal surgery, body mass index greater than or equal to 35 kg/m2, and Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score greater than or equal to 26. Patients were randomized to PEEP of 4 cm H2O (n = 19) or a recruitment maneuver followed by PEEP of 12 cm H2O (n = 21) in the PROBESE study. In the single-center study, they were randomized to PEEP of 5 cm H2O (n = 25) or a recruitment maneuver followed by individualized PEEP (n = 25) determined by electrical impedance tomography. Primary endpoint was Pao
2/inspiratory oxygen fraction before extubation and secondary endpoints included intraoperative tidal volume distribution to dependent lung and driving pressure.

Results
Ninety patients were evaluated in three groups after combining the two lower PEEP groups. Median individualized PEEP was 18 (interquartile range, 16 to 22; range, 10 to 26) cm H2O. Pao
2/inspiratory oxygen fraction before extubation was 515 (individual PEEP), 370 (fixed PEEP of 12 cm H2O), and 305 (fixed PEEP of 4 to 5 cm H2O) mmHg (difference to individualized PEEP, 145; 95% CI, 91 to 200; P < 0.001 for fixed PEEP of 12 cm H2O and 210; 95% CI, 164 to 257; P < 0.001 for fixed PEEP of 4 to 5 cm H2O). Intraoperative tidal volume in the dependent lung areas was 43.9% (individualized PEEP), 25.9% (fixed PEEP of 12 cm H2O) and 26.8% (fixed PEEP of 4 to 5 cm H2O) (difference to individualized PEEP: 18.0%; 95% CI, 8.0 to 20.7; P < 0.001 for fixed PEEP of 12 cm H2O and 17.1%; 95% CI, 10.0 to 20.6; P < 0.001 for fixed PEEP of 4 to 5 cm H2O). Mean intraoperative driving pressure was 9.8 cm H2O (individualized PEEP), 14.4 cm H2O (fixed PEEP of 12 cm H2O), and 18.8 cm H2O (fixed PEEP of 4 to 5 cm H2O), P < 0.001.

Conclusions
This secondary analysis of obese patients undergoing laparoscopic surgery found better oxygenation, lower driving pressures, and redistribution of ventilation toward dependent lung areas measured by electrical impedance tomography using individualized PEEP. The impact on patient outcome remains unclear.

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