Background and Goal of Study:
Induction of anesthesia frequently causes atelectasis, which, in obese patients, reduces end-expiratory lung volume by about 50%1 and may increase other
pulmonary complications after surgery.2 During mechanical ventilation, tidal recruitment and collapse may occur due to insufficient positive end-expiratory
pressure (PEEP) and may promote lung injury. Following a recruitment maneuver (RM), individualized setting of PEEP can be performed by Electric Impedance
Tomography (EIT)-based regional ventilation delay index (RVDi).3 We hypothesized that individualized PEEPEIT+RM will improve lung compared to a standard
PEEP (5 cmH2O) in obese and non-obese patients during general anesthesia for laparoscopic abdominal surgery.
Materials and Methods:
After institutional ethical committee approval and written informed consent, patients were prospectively arranged in an obese group (BMI ≥ 35 kg/m2) and a nonobese
group (BMI between 18.5 and 30 kg/m2). Patients were randomized to receive ventilation (VT=8ml/kg predicted body weight, I:E ratio 1:2, respiratory rate
of 12/min) with either standard (PEEP5) or individualized PEEPEIT. PEEPEIT patients received a RM (plateau pressure 40 or 50 cmH2O for 10 breaths; PEEP of 20
or 26 cmH2O, higher values in obese patients) followed by decremental PEEP-titration (steps of 2cmH2O). On every PEEP-step, a low-flow breath was performed
to assess lung inhomogeneity by RVDi
3 and PEEPEIT was selected at the RVDi minimum. PaO2/FIO2 was measured before and after intubation, during
capnoperitoneum, before and 2 hours after extubation. Data were compared using repeated measures ANOVA except for PEEP, which was tested by Kruskal-
Wallis-test due to non-normal distribution.
Results and Discussion:
90 patients (PEEP5 n=45, PEEPEIT n=45) completed the study with BMI 25.5±2.4 kg/m2 in normal weight group (n=40) and BMI 50.0±7.9 kg/m2 in the obese
group (n=50). PEEPEIT was significantly higher in both groups (normal weight: median 14 cmH2O [8;20]; obese: 18 cmH2O [10;26]) than the PEEP5 (p<0.001).
With PEEPEIT, patients had better oxygenation (p<0.001, table 1), higher significant compliance and lower driving pressure intraoperatively (p<0.001).
Conclusion:
In patients undergoing laparoscopic abdominal surgery, inhomogeneity of lung inflation can be reduced by RM and PEEP-titration guided by EIT. This requires
higher PEEP values than commonly recommended and improved oxygenation with reduced driving pressures.
References:
1 Nestler C et al. Br J Anaesth. 2017 Oct 16. doi: 10.1093/bja/aex192.
2 Serpa Neto A et al. JAMA 2012; 308: 1651-59.
3 Muders T et al. Crit Care Med 2012; 40:903-911.


03 / Individualized PEEP-adjustment in obese and non-obese patients undergoing laparoscopic abdominal surgery