Individualized versus Fixed Positive End-expiratory Pressure for Intraoperative Mechanical Ventilation in Obese Patients: A Secondary Analysis

Abstract

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 Pao2/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. Pao2/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. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Optimized ventilation strategy for surgery on patients with obesity from the perspective of lung protection: A network meta-analysis

“…We also excluded 1 article after sensitivity analysis. Finally, 23 RCTs were included ( 12 , 20 – 41 ), which involved a total of 3,364patients with obesity who were randomized to 13 ventilation strategies ( Figure 1 ). Information extracted from each article included the first author, publication year, design of the study, surgery type, patient data (age, country, American Society of Anesthesiologists physical status classification [ASA], BMI and sample size), ventilation strategy, outcome measures (PaO2/FiO2, intraoperative lung compliance, postoperative pulmonary atelectasis) ( Table 1 ).…”

“…In summary, 1 study ( 42 ) was assessed as having a high bias risk and was excluded. Two studies were assessed as being unclear ( 33 , 35 ), and the rest deemed to be low risk ( 12 , 20 – 32 , 34 , 36 – 41 ). All studies were symmetrically distributed within the funnel plot, indicating no publication bias (supporting information Figures S9–S11 ).…”

“…There were 17 RCTs (20)(21)(22)(23)(24)(25)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41) involving a total of 985 patients with obesity, which assessed the MD of the overall effect size of the intraoperative PaO 2 /FiO 2 across the 11 ventilation strategies (Figure 2). The network meta-analysis showed that the ventilation strategy volume-controlled ventilation with individualized positive end-expiratory pressure and recruitment maneuver (VCV+PEEPind+RM) was more efficacious in improving PaO 2 /FiO 2 than pressure-controlled ventilation (PCV), volume-controlled ventilation (VCV), volume-controlled ventilation with recruitment maneuver (VCV+RM), VCV+lowPEEP or volume-controlled ventilation with lower positive expiratory end pressure and recruitment maneuver (VCV+lowPEEP+RM), MD [95% CI] and [quality of evidence]: 162.…”

Methods for Determination of Individual PEEP for Intraoperative Mechanical Ventilation Using a Decremental PEEP Trial

“…This leads to lower elastance of the respiratory system and consecutively improves oxygenation during surgery [28,30,31]. Many authors have advocated the individualization of PEEP in the operating room [32,33], and there is recent evidence that individualized PEEP is superior to a standardized "one PEEP fits all" strategy, even if higher PEEP levels are routinely used [7]. The optimal method for the choice of best PEEP during mechanical ventilation in the operating room is, however, less clear [34].…”

“…We have recently shown that an individualized PEEP (PEEP IND ) titration using electric impedance tomography (EIT) in obese patients resulted in a PEEP range of 10-26 cm H 2 O with a median of 18 cm H 2 O when selecting PEEP according to the lowest temporal inhomogeneity determined by the regional ventilatory delay (RVD I method) [6]. The comparison with a subgroup of patients of the large PROBESE trial comparing standard higher PEEP of 12 cm H 2 O vs. PEEP of 4 cm H 2 O suggested that lung recruitment was incomplete in both arms of the PROBESE trial [7]. Likewise, even in non-obese patients, the PEEP IND determined by EIT was found as high as median of 14 cm H 2 O (median, range of 8-20 cm H 2 O) [4].…”