Effect of low-dose ketamine on MAC_BAR of sevoflurane in laparoscopic cholecystectomy: A randomized controlled trial

Low-dose ketamine can reduce the minimum alveolar concentration of sevoflurane necessary to block the adrenergic response (MAC_BAR ) in animals. However, the effects of low-dose ketamine on the sevoflurane MAC_BAR in patients undergoing laparoscopic surgery are unclear. The aim of this study was to investigate the effects of three different low doses of ketamine on the MAC_BAR of sevoflurane in patients undergoing laparoscopic cholecystectomy.

One hundred patients who underwent laparoscopic cholecystectomy were enrolled. After general anaesthesia induction and tracheal intubation, patients received sevoflurane anaesthesia in combination with a loading dose of saline followed by infusion or a loading dose of 0.5 mg/kg ketamine followed by a continuous infusion of 5 (K₁ group), 10 (K₂ group) and 20 μg/kg/min (K₃ group). The target concentration of end-tidal sevoflurane was maintained for at least 20 minutes before carbon dioxide pneumoperitoneum stimulus. The MAC_BAR of sevoflurane in each group was determined by using an up-and-down sequential allocation technique.

Seventy-one patients completed the study. The values of MAC_BAR for sevoflurane were 5.3% in the K₀ , 4.8% in K₁ , 3.3% in K₂ and 3.2% in K₃ groups. The use of ketamine significantly reduced the MAC_BAR of sevoflurane compared to sevoflurane alone. The K₂ and K₃ groups showed significantly lower values of MAC_BAR than that in the K₁ group. However, a higher dose of ketamine in the K₃ group did not further reduce the sevoflurane MAC_BAR . The mean arterial blood pressure (MAP) values before pneumoperitoneum in the K₂ and the K₃ groups were significantly higher compared to those in the K₀ and K₁ groups. Compared with the values before pneumoperitoneum, the heart rate and MAP after pneumoperitoneum were significantly increased. Overall, the haemodynamics remained stable during the study period in all groups.

A loading dose of 0.5 mg/kg ketamine followed by a continuous infusion of 10.0 μg/kg/min led to a significant decrease in the MAC_BAR of sevoflurane in patients undergoing laparoscopic cholecystectomy.