"Comparison of the Effects of Volume-Controlled Ventilation and Pressure-Controlled Ventilation Modes on Compliance and End-Tidal CO2 In Patients Undergoing Laparoscopic Cholecystectomy"

Laparoscopic cholecystectomy is one of the most commonly performed surgical procedures under general anesthesia. Creation of carbon dioxide pneumoperitoneum during laparoscopic surgery increases intra-abdominal pressure, resulting in reduced functional residual capacity, decreased lung compliance, increased airway pressures, and alterations in carbon dioxide elimination. These physiological changes may impair respiratory mechanics and increase the risk of perioperative pulmonary complications. Therefore, selection of an appropriate mechanical ventilation strategy is essential to maintain adequate ventilation and optimize respiratory function during laparoscopic surgery. The objective of this randomized controlled trial is to compare the effects of volume-controlled ventilation and pressure-controlled ventilation on static lung compliance and end-tidal carbon dioxide (EtCO₂) in adult patients undergoing elective laparoscopic cholecystectomy under general anesthesia. The study aims to determine whether pressure-controlled ventilation provides superior intraoperative respiratory mechanics compared with volume-controlled ventilation while maintaining adequate ventilation throughout the surgical procedure.

This is a prospective, single-center, randomized controlled trial conducted in the Department of Anaesthesia, Nishtar Hospital, Multan. A total of 60 adult patients aged 25-50 years, of either sex, classified as American Society of Anesthesiologists (ASA) physical status I or II and scheduled for elective laparoscopic cholecystectomy, will be enrolled after obtaining written informed consent. Patients with uncontrolled cardiopulmonary disease, diabetes mellitus, significant renal or hepatic impairment, chronic systemic illness, body mass index below 18.5 kg/m² or above 24.9 kg/m², or recent respiratory tract infection within the preceding three weeks will be excluded.

Participants will be allocated in a 1:1 ratio using computer-generated randomization by an independent third party into one of two study groups. Group A will receive volume-controlled ventilation, while Group B will receive pressure-controlled ventilation. Allocation concealment will be maintained until initiation of mechanical ventilation. Baseline demographic variables including age, sex, and body mass index will be recorded before induction of anesthesia.

A standardized anesthetic technique will be used for all participants. Mechanical ventilation settings will include a tidal volume of 8 mL/kg (with inspiratory pressure adjusted in the PCV group to achieve the target tidal volume), respiratory rate initially set at 12 breaths per minute and subsequently adjusted to maintain an end-tidal carbon dioxide concentration between 32 and 38 mmHg, inspiratory-to-expiratory ratio of 1:2, fraction of inspired oxygen (FiO₂) of 0.40, positive end-expiratory pressure (PEEP) of 5 cmH₂O, and oxygen saturation maintained above 95%. Carbon dioxide pneumoperitoneum will be maintained with an intra-abdominal pressure of 12-15 mmHg throughout the procedure.

Static lung compliance and end-tidal carbon dioxide will be recorded at three predefined intraoperative time points: five minutes after induction of anesthesia, fifteen minutes after carbon dioxide insufflation in the reverse Trendelenburg position, and ten minutes after carbon dioxide desufflation. Measurements will be recorded using the integrated monitoring systems of the anesthesia workstation by a trained anesthesiologist who is not involved in group allocation. Blinding of the anesthesia provider is not feasible because of the nature of the interventions; however, the primary outcome measures are objective monitor-derived variables, minimizing the risk of measurement bias.