Impact of PEEP during laparoscopic surgery on early postoperative ventilation distribution visualized by electrical impedance tomography

Abstract

Background: General anesthesia, mechanical ventilation and pneumoperitoneum affect ventilation distribution at different extent. It should be clarified if an intraoperative positive end-expiratory pressure (PEEP) level of 10 cmH2O influences early postoperative ventilation. Electrical impedance tomography (EIT) was used to assess changes in regional ventilation.

Methods: Thirty-two patients (ASA physical status I/II) scheduled to undergo elective laparoscopic cholecystectomy were enrolled. The patients were randomly assigned to PEEP (10 cmH2O) or ZEEP group (0 cmH2O). EIT was performed before induction of anesthesia (T0) and after admission to the recovery room (T1-4). Ventral/dorsal and right/left lung impedance ratio (IR) and the center-of-ventilation index (COV) were calculated to investigate the differences in homogeneity of ventilation.

Results: Compared to preoperative data a significant increase in PaCO2 and reduction of pH values could be found in both groups. Significant decrease of postoperative tidal impedance change (∆Z) as well as a general postoperative ventral shift of the ventilation indicated by changes of IR and COV could be found in both groups. In ZEEP group IR and COV differed significantly from baseline (T0). In PEEP group there was just significant difference in COV at T2-T4 compared to T0. In the early postoperative period (T1) there was no difference in ventilation distribution in PEEP patients.

Conclusion: Changes of postoperative ventilation can be imaged by EIT. Intraoperative PEEP ventilation has a positive effect on early postoperative ventilation distribution, even though not all PEEP patients benefit from mechanical PEEP ventilation the same way. Intraoperative PEEP results in a more homogeneous ventilation distribution by trend.