Physiological effects of the open lung approach during laparoscopic cholecystectomy: focus on driving pressure.

BACKGROUND: During laparoscopy, respiratory mechanics and gas exchange are impaired because of pneumoperitoneum and atelectasis formation. We applied an open lung approach (OLA) consisting in lung recruitment followed by a decremental positive-end expiratory pressure (PEEP) trial to identify the level of PEEP corresponding to the highest compliance of the respiratory system (best PEEP). Our hypothesis was that this approach would improve both lung mechanics and oxygenation without hemodynamic impairment.

METHODS: We studied twenty patients undergoing laparoscopic cholecystectomy. We continuously recorded respiratory mechanics parameters throughout a decremental PEEP trial in order to identify the best PEEP level. Furthermore, lung and chest wall mechanics, respiratory and transpulmonary driving pressures (ΔP), gas exchange and hemodynamics were recorded at three time-points: 1) after pneumoperitoneum induction (TpreOLA); 2) after the application of the OLA (TpostOLA); 3) at the end of surgery, after abdominal deflation (Tend).

RESULTS: The "best PEEP" level was 8.1±1.3 cmH2O (range 6 to 10 cmH2O), corresponding to the highest compliance of the respiratory system (CRS). This "best PEEP" level corresponded with lowest ΔPL. OLA increased the compliance of the lung and of the chest wall, and decreased ΔPRS and ΔPL. PaO2/FiO2 increased from 299±125 mmHg to 406±101 mmHg (P=0.04). Changes in respiratory mechanics, driving pressures and oxygenation were maintained until Tend. Hemodynamic parameters remained stable throughout the study period.

CONCLUSIONS: In patients undergoing laparoscopic cholecystectomy, the OLA was suitable for bedside PEEP setting, improved lung mechanics and gas exchange without significant adverse hemodynamic effects.