Intraoperative positive end-expiratory pressure evaluation using the intratidal compliance-volume profile

Background. Lung-protective mechanical ventilation during general surgery including the application of PEEP can reduce postoperative pulmonary complications. In a prospective clinical observation study, we evaluated volume-dependent respiratory system compliance in adult patients undergoing ear-nose-throat surgery with ventilation settings chosen empirically by the attending anaesthetist. Methods. In 40 patients, we measured the respiratory variables during intraoperative mechanical ventilation. All measurements were subdivided into 5 min intervals. Dynamic compliance (C-RS) and the intratidal volume-dependent C-RS curve was calculated for each interval and classified into one of the six specific compliance profiles indicating intratidal recruitment/derecruitment, overdistension or all. We retrospectively compared the occurrences of the respective compliance profiles at PEEP levels of 5 cm H2O and at higher levels. Results. The attending anaesthetists set the PEEP level initially to 5 cm H2O in 29 patients (83%), to 7 cm H2O in 5 patients (14%), and to 8 cm H2O in 2 patients (6%). Across all measurements the mean C-RS was 61 (11) ml cm H2O-1 (40-86 ml cm H2O-1) and decreased continuously during the procedure. At PEEP of 5 cm H2O the compliance profile indicating strong intratidal recruitment/derecruitment occurred more often (18.6%) compared with higher PEEP levels (5.5%, P<0.01). Overdistension was practically never observed. Conclusions. In most patients, a PEEP of 5 cm H2O during intraoperative mechanical ventilation is too low to prevent intratidal recruitment/derecruitment. The analysis of the intratidal compliance profile provides the rationale to individually titrate a PEEP level that stabilizes the alveolar recruitment status of the lung during intraoperative mechanical ventilation.