Effects of Variable Ventilation on Gas Exchange in an Experimental Model of Capnoperitoneum: A Randomized Crossover Study.

Background: The rapid advancement of minimally invasive surgical techniques has made laparoscopy a preferred alternative because it reduces postoperative complications. However, inflating the peritoneum with CO 2 causes a cranial shift of the diaphragm decreasing lung volume and impairing gas exchange. Additionally, CO 2 absorption increases blood CO 2 levels, further complicating mechanical ventilation when the lung function is already compromised. Standard interventions such as lung recruitment maneuvers or increasing positive end-expiratory pressures can counteract these effects but also increase lung parenchymal strain and intrathoracic pressure, negatively impacting cardiac output. The application of variability in tidal volume and respiratory rate during mechanical ventilation to mimic natural breathing has shown benefits in various respiratory conditions. Therefore, we aimed to evaluate the short-term benefits of variable ventilation (VV) on gas exchange, respiratory mechanics, and hemodynamics during and after capnoperitoneum, compared to conventional pressure-controlled ventilation (PCV).

Methods: Eleven anaesthetized rabbits were randomly assigned to PCV or VV. Oxygenation index (Pa o2 /FiO 2 ), arterial partial pressure of carbon dioxide (Pa co2 ), and respiratory mechanical parameters were assessed after a 15-minute-long ventilation period before, during, and after capnoperitoneum. According to a crossover design, after measurements at the 3 different stages, the ventilation mode was changed, and the entire sequence was repeated.

Results: Capnoperitoneum compromised respiratory mechanics, decreased oxygenation, and caused CO 2 -retention compared to baseline measurements under both ventilation modalities ( P < .05, for all). Application of VV resulted in lower Pa o2 /FiO 2 (405. 5 ± 34.1 (mean ± standard deviation [SD]) vs 370. 5 ± 44.9, P < .001) and higher Pa co2 (48. 4 ± 5.1 vs 52. 8 ± 6.0 mm Hg, P = .009) values during capnoperitoneum compared to PCV. After abdominal deflation and a lung recruitment maneuver, VV proved more beneficial for CO 2 removal than PCV (41. 0 ± 2.3 vs 44. 6 ± 4.3mmHg, P = .027). No significant difference was observed in the respiratory mechanical or hemodynamic parameters between the ventilation modalities under the same conditions.

Conclusions: The detrimental effects of capnoperitoneum on gas exchange were more pronounced with VV. However, after the release of capnoperitoneum, VV significantly improved CO 2 clearance. Therefore, VV could possibly be considered as an alternative ventilation modality to restore physiological gas exchange after, but not during, capnoperitoneum.