Comparison of Pressure-Controlled Ventilation Mode and Volume-Controlled Ventilation Mode in Elective Laparoscopic Cholecystectomy Surgeries

Elective laparoscopic cholecystectomy is the most frequently performed procedure for the treatment of cholelithiasis and chronic cholecystitis.  Compared to open surgery, laparoscopic surgery has several advantages, which include the use of smaller incisions, less postoperative pain, and rapid recovery. Inherent to laparoscopy is pneumoperitoneum and steep patient positioning, which may sometimes severely impact the pulmonary mechanics, reducing the lung compliance, elevating the airway pressure, and altering the gas exchange (1). These changes present a challenge for the anesthetic management, specifically in the provision of satisfactory ventilation and oxygenation. Therefore, the decision on the mode of mechanical ventilation during such procedures is a very significant aspect to be taken into account in the practice of anesthesia. There are two major modes that are used in general anesthesia to help meet the patient's respiratory requirements. These include volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV). In VCV mode, a predetermined tidal volume is administered with each breath, which maintains a steady minute ventilation, but can also increase the peak airway pressure, particularly when pneumoperitoneum is set up (2). PCV, on the other hand, utilizes a predetermined inspiratory pressure and variable tidal volumes based on the compliance of the lungs and is linked to reduced peak airway pressures and a decreasing flow pattern that can improve distribution of ventilation (3). These inherent dissimilarities have clinical inferences: increased airway pressures may tend to precondition barotrauma in patients and impede venous return; however, enhanced compliance could improve the gas exchange and diminish ventilator-associated lung injury. A number of randomized clinical trials and comparative studies have studied the effects of PCV and VCV in patients who have undergone laparoscopic cholecystectomy. One of the studies conducted by Tyagi et al. (4) showed that PCV led to much lower peak airway pressures and higher mean airway pressures than VCV with an equal level of haemodynamic stability and gas exchange profiles.

In a similar study by Aydin et al., they found that VCV achieved improved alveolar ventilation following pneumoperitoneum as indicated by the difference in alveolar-arterial gradients despite similar respiratory mechanics in both modes (5). Recent review also indicates that PCV can be used to have benefits in terms of decreasing peak airway pressures and improving oxygenation even in laparoscopic settings, which can potentially reduce the risk of ventilator-induced lung injury (3). However, there is inconclusive evidence on the superiority of one of the two modes compared to another, with researchers finding little difference in respiratory and haemodynamic results of both methods (6). Hence, additional studies are justified to find out the extent to which particular groups of patients or intraoperative factors respond to a ventilation mode more favorably. This study aimed to compare the clinical outcomes of pressure-controlled ventilation and volume-controlled ventilation modes in elective laparoscopic cholecystectomy in terms of intraoperative respiratory mechanics, gas exchange, and haemodynamic stability.

A total of 80 cases, equally distributed in two groups, were used to determine the outcomes of this study. The demographic profile of the cohort is given in Table 1. Analysis of the table showed that the distribution of cases was equal in both groups with no statistically significant differences in any of the characteristics, including age, sex, ASA physical status, and duration of surgery and duration of pneumoperitoneum. The analysis of baseline vital parameters, including blood pressure, pulse rate, SpO_2, and ABG, was distributed similarly between the two groups. The results show that the two groups were well matched and no potential confounding factor existed between the groups, which could influence the results.

Intraoperative Ventilatory Parameters are given in Table 2. Peak airway pressure (P peak) and plateau pressure (P plateau) were found to be significantly lower in the PCV group at all measured time intervals (p < 0.001). The difference was more significant after CO₂ insufflation. VCV showed markedly higher airway pressures. This indicates that PCV better accommodates reduced lung compliance during pneumoperitoneum by limiting airway pressure. End-tidal CO₂ (EtCO₂) values were slightly lower in the PCV group at most time points, with statistically significant differences after CO₂ insufflation and during later intraoperative periods. These findings suggest improved CO₂ elimination with PCV during pneumoperitoneum. Therefore, PCV demonstrated superior ventilatory mechanics, particularly under the stress of increased intra-abdominal pressure.

Hemodynamic Parameters in the cohort at different intervals of time are given in Table 3. The hemodynamic variables (BP, HR, SpO₂) were found to be similar between the two groups at all intraoperative time points. Although transient increases in blood pressure and heart rate were observed after CO₂ insufflation in both groups, the differences were not statistically significant. This indicates that both ventilation modes maintained similar hemodynamic stability during laparoscopic surgery.

Arterial Blood Gas and Pulmonary Parameters values are depicted in Table 4. The overall analysis of the table showed that at skin closure, the PCV group showed significantly better gas exchange. The PCV group had a higher pH (p = 0.048), lower pCO₂ (p = 0.004), and higher pO₂ (p = 0.002). More importantly, the calculated pulmonary parameters favored the PCV method with higher oxygenation index (PaO₂/FiO₂), higher dynamic compliance, lower alveolar-arterial oxygen gradient (A-a DO₂), and lower dead space ventilation ratio (VD/VT). All these differences were statistically significant (p < 0.001). These findings indicate better oxygenation, improved lung compliance, and more efficient ventilation-perfusion matching with PCV.

Comparison of changes from baseline and recovery characteristics in the two groups is given in Table 5.  The increase in pCO₂ from baseline was significantly greater in the VCV group (p < 0.001), indicating comparatively reduced CO₂ clearance. Similarly, improvement in pO₂ was significantly greater in the PCV group (p = 0.002). Mean peak airway pressure and mean EtCO₂ during surgery were significantly lower in the PCV group. However, recovery characteristics, including time to extubation, Aldrete score at 10 minutes, and incidence of PONV, were comparable between groups. This suggests that although PCV improved intraoperative respiratory mechanics and gas exchange, it did not significantly alter immediate postoperative recovery outcomes.

The results of this study show that pressure-controlled ventilation (PCV) has tremendous benefits over volume-controlled ventilation (VCV), especially in terms of airway pressures, pulmonary mechanics, and gas exchange without compromising hemodynamic stability and recovery features in patients undergoing elective laparoscopic cholecystectomy. The presence of pneumoperitoneum in the laparoscopic surgery enhances pressure in the abdominal cavity, which causes a cephalad displacement of the diaphragm, a decrease in functional residual capacity, and a decrease in pulmonary compliance (1). These changes are normally known to be related to elevated airway pressures and the absence of ventilation-perfusion matching. Peak and plateau airway pressures in the current study were significantly and continuously reduced in the PCV group at all time points during the intraoperative period, especially at the time following CO2 insufflation. This observation is in line with the earlier research that has reported that the slowing inspiratory flow pattern of PCV facilitates the more homogenous alveolar distribution of tidal volume and lower peak inspiratory pressure than VCV (7,8). After pneumoperitoneum, the increase in airway pressures was more pronounced, which confirms the hypothesis that PCV is superior in terms of being able to adapt to decreased lung compliance during laparoscopy. Tyagi et al. have also found reduced peak airway pressures on PCV during laparoscopic cholecystectomy without affecting minute ventilation (9). The clinical significance of lower airway pressures is that they decrease the incidence of barotrauma and decrease the negative impact on the venous return and cardiac output. The PCV group had a much better gas exchange at skin closure due to improved airway mechanics. The levels of pCO₂ in the arteries were lower, pO2 was higher, and the oxygenation index (ratio of PaO2/FiO2) was much better than in the VCV group. A decreased dead space fraction (VD/VT) in the PCV group and lower alveolar-arterial oxygen gradient indicate enhanced matching ventilation-perfusion. Aydin et al. [4] have reported similar results, which showed an improvement in oxygenation and compliance parameters in the laparoscopic procedures with PCV. Its beneficial impact on the lung mechanics is further supported by the fact that the dynamic compliance was improved in the PCV group in the current study. Although there were respiratory benefits, hemodynamic measures (blood pressure, heart rate, and oxygen saturation) were similar across the groups during surgery. This indicates that the two ventilation modes are safe from a cardiovascular standpoint in laparoscopic cholecystectomies of ASA I & 2 patients. Minimal hemodynamic changes between PCV and VCV in laparoscopy have also been reported in the previous comparative trials (10).  Notably, the postoperative recovery outcomes, such as time to extubation, Aldrete score, and postoperative nausea and vomiting, were not significantly different in terms of recovery between groups. It means that PCV does not have a negative impact on the postoperative outcomes in the short term but only enhances intraoperative respiratory performance. The results of this study are consistent with the existing evidence that indicates that PCV has even better control of airway pressures and improved oxygenation during laparoscopic surgery, particularly when pneumoperitoneum is observed. Although the two ventilation modes are both clinically acceptable, PCV can be a better option in those patients where limiting airway pressures and optimization of pulmonary mechanics are a priority.

Within the limitations of the current study, we found that pressure-controlled ventilation (PCV) showed advantages over volume-controlled ventilation (VCV) for elective laparoscopic cholecystectomy. It provided lower peak and plateau airway pressures, better oxygenation, improved dynamic compliance, and effective carbon dioxide elimination following pneumoperitoneum. Although both modes had similarities as far as hemodynamic and recovery profiles were concerned. The volume-controlled ventilation was able to produce adequate ventilation, but it was associated with higher airway pressures, which were relatively less favourable for gas exchange. Therefore, pressure-controlled ventilation must be preferred in cases where minimizing airway pressures and optimizing pulmonary mechanics are priorities.