Anesthesia for laparoscopic cholecystectomy: Is nitrous oxide contraindicated?

Since it has been suggested that the use of nitrous oxide (N₂O) may contribute to bowel distention, we evaluated the effects of N₂O on operating conditions during laparoscopic cholecystectomy in 50 healthy patients using a double-blind protocol design. All patients received the same preanesthetic medication (midazolam, 2 mg intravenously) and induction of anesthesia consisted of intravenously administered fentanyl 1.5 μg·kg^-1, thiopental 4-6 mg·kg^-1, and a nondepolarizing muscle relaxant. For maintenance of anesthesia, patients were randomly assigned to one of two treatment groups: group 1 (n = 26) received isoflurane with 70% N₂O in oxygen (O₂), whereas group 2 (n = 24) received isoflurane in an air/O₂ mixture. The surgeon (blinded to the anesthetic technique) estimated the degree of technical difficulty before beginning the operation using a five-point scale. At 15-min intervals throughout the operation, the surgeon was asked to evaluate both 'overall operating conditions' and degree of 'bowel distension' using independent five-point scales. At the end of the operation, the surgeon was asked whether or not N₂O had been used as part of the anesthetic technique. There were no significant intraoperative differences between the two groups with respect to operating conditions or bowel distension. More importantly, there was no time-related change in either variable during the course of the operation. Finally, the incidence of postoperative nausea and vomiting was similar in both treatment groups. The surgeon was able to correctly determine that N₂O had been administered only 44% of the time. Thus, N₂O had no clinically apparent deleterious effects during laparoscopic cholecystectomy.