Effect of prolonged inspiratory time on gas exchange during robot-assisted laparoscopic urologic surgery

Background

Gas exchange disturbance may develop during urologic robotic laparoscopic surgery with the patient in a steep Trendelenburg position. This study investigated whether prolonged inspiratory time could mitigate gas exchange disturbances including hypercapnia.

Methods

In this randomized cross-over trial, 32 patients scheduled for robot-assisted urologic surgery were randomized to receive an inspiratory to expiratory time ratio (I:E) of 1:1 for the first hour of pneumoperitoneum followed by 1:2 for last period of surgery (group A, n?=?17) or I:E of 1:2 followed by 1:1 (group B, n?=?15). Arterial blood gas analysis, airway pressure and hemodynamic variables were assessed at four time points (T1: 10?min after induction of general anesthesia, T2: 1?h after the initiation of pneumoperitoneum, T3: 1?h after T2 and T4: at skin closure). The carry over effect of initial I:E was also evaluated over the next hour through arterial blood gas analysis.

Results

There was a significant decrease in partial pressure of oxygen in arterial blood (PaO₂) for both groups at T2 and T3 compared to T1 but in group B the PaO₂ at T4 was not decreased from the baseline. Partial pressure of carbon dioxide in arterial blood (PaCO₂) increased with I:E of 1:2 but did not significantly increase with I:E of 1:1; however, there were no differences in PaO₂ and PaCO₂ between the groups.

Conclusion

Decreased oxygenation by pneumoperitoneum was improved and PaCO₂ did not increase after 1 h of I:E of 1:1; however, the effect of equal ratio ventilation longer than 1 h remains to be determined. There was no carryover effect of the two different I:E ratios.