Comparison of arterial to end-tidal carbon dioxide gradient P (a-ET)CO2 in volume versus pressure controlled ventilation in patients undergoing robotic abdominal surgery in the Trendelenburg position. A randomised controlled study

Background and Aims: Robotic surgery is increasingly prevalent as an advancement in care. Steep head-down positions in pelvic surgery can increase the ventilation-perfusion mismatch and increase ventilatory requirements to offset carbon dioxide (CO 2 ) increases consequent to pneumoperitoneum. The primary objective was to assess the impact of two ventilatory strategies, volume versus pressure-controlled ventilation on the arterial to end-tidal carbon dioxide gradient P (a-ET)CO 2 in patients undergoing robotic surgery in the Trendelenburg position. The effects on alveolar to arterial oxygen gradient P (A-a)O 2 , peak airway pressure (P aw ) , dynamic compliance (C dyn ) and haemodynamics were also assessed. Methods: Fifty-one patients, 18-75 y, American Society of Anesthesiologists I-III undergoing robotic surgery in Trendelenburg position were randomised to volume-controlled ventilation (Group VCV) or pressure-controlled ventilation (Group PCV). The P (a-ET)CO 2 was measured at baseline T0, 10 min after Trendelenburg position T1, 2 h of surgery T2, 4 h T3 and at T e, 10 min after deflation. The P (A-a) O 2 , P aw , C dyn , heart rate and blood pressure were also measured at the same time. Results: The P (a-ET)CO 2 at T1, T2, T3 and at T e was lower in Group PCV versus Group VCV. The P aw was lower at T1, T2, and T3 and C dyn higher at T3 and Te in Group PCV at comparable minute ventilation. Haemodynamics and P (A-a)O 2 were comparable between the groups. Conclusion: Pressure-controlled ventilation reduces P (a-ET)CO 2 gradient, P aw and improves C dyn but does not affect P (A-a) O 2 or haemodynamics in comparison to volume-controlled ventilation in robotic surgeries in the Trendelenburg position.