Effect of nitrous oxide on post-operative nausea and vomiting during propofol anaesthesia for short surgical operations.

One hundred patients of ASA status I or II, undergoing gynaecological or urological surgery were studied. Opioids were omitted from premedication and anaesthesia. Patients were allocated randomly to one of two equal groups and were anaesthetized using a computer controlled infusion system, programmed to achieve theoretically any target blood propofol concentration. One group received 60% nitrous oxide in oxygen while the other group received 100% oxygen. Six patients in the nitrous oxide group had nausea and three of these patients vomited. Two patients in the oxygen group had nausea but no patient vomited. The frequency of nausea and vomiting in the two groups was not statistically different (P > 0.05). Theoretical blood propofol concentration shown to produce surgical anaesthesia was maintained in all patients. However 12% of the patients that received nitrous oxide and 40% of the patients that did not, responded to the surgical stimulus by limb movement. Patients in the oxygen group required higher rates of propofol infusion to maintain surgical anaesthesia.