Modeling intra-abdominal volume and respiratory driving pressure during pneumoperitoneum insufflation - a patient-level data meta-analysis.

During pneumoperitoneum, intra-abdominal pressure (IAP) is usually kept at 12-14 mmHg. There is no clinical benefit in IAP increments if they do not increase intra-abdominal volume IAV. We aimed to estimate IAV (ΔIAV) and respiratory driving pressure changes (ΔPRS) in relation to changes in IAP (ΔIAP). We carried out a patient-level meta-analysis of 204 adult patients with available data on IAV and ΔPRS during pneumoperitoneum from three trials assessing the effect of IAP on postoperative recovery and airway pressure during laparoscopic surgery under general anesthesia. The primary endpoint was ΔIAV, and the secondary endpoint was ΔPRS. The endpoints' response to ΔIAP was modeled using mixed multivariable Bayesian regression to estimate which mathematical function best fitted it. IAP values on the pressure-volume (PV) curve where the endpoint rate of change according to IAP decreased were identified. Abdomino-thoracic transmission (ATT) rate, i.e., the rate ΔPRS changeto ΔIAP, was also estimated. The best-fitting function was sigmoid logistic and linear for IAV and ΔPRS response, respectively. Increments in IAV reached a plateau at 6.0 [95%CI 5.9 to 6.2] L. ΔIAV for each ΔIAP decreased at IAP ranging from 9.8 [95%CI 9.7 to 9.9], to 12.2 [12.0 to12.3] mmHg. ATT rate was 0.65 [95%CI 0.62 to 0.68]. One mmHg of IAP raised ΔPRS 0.88 cmH2O. During pneumoperitoneum, IAP has a non-linear relationship with IAV and a linear one with ΔPRS. IAP should be set below the point where IAV gains diminish.