Inspired oxygen fraction of 0.8 compared with 0.4 does not further reduce postoperative nausea and vomiting in dolasetron-treated patients undergoing laparoscopic cholecystectomy

Background. Postoperative nausea and vomiting (PONV) is one of the most frequent complications after general anaesthesia. Single-dose antiemetic prophylaxis has limited efficacy in high-risk patients. Adding a simple potential antiemetic approach, such as increasing the inspired oxygen fraction, to the antiemetic portfolio would preserve pharmacological interventions for treatment of symptoms in the postoperative period. However, the antiemetic effect of a high inspired oxygen fraction is still discussed controversially. The aim of the study was to evaluate whether an inspired oxygen fraction of 0.8 decreases PONV in patients receiving the 5-HT3-antagonist dolasetron. Methods. In a randomized, placebo-controlled, double-blinded trial we studied 377 patients (ASA I-III) undergoing elective laparoscopic cholecystectomy. Induction of anaesthesia was standardized, including thiopental fentanyl and cis-atracurium. For all patients the individual risk for PONV was calculated using the Koivuranta score and all patients received 12.5 mg dolasetron i.v. before surgery. Patients were allocated randomly to one of three groups: Group A (n=125) received 80% oxygen in air, Group B (n=125) 40% oxygen in air and Group C (n=127) 40% oxygen in nitrous oxide. Postoperative nausea, postoperative vomiting (PV), or nausea, vomiting, or both (PONV) was assessed in the early (0-4 h) and overall postoperative period (0-24 h) by an anaesthesiologist unaware of patient allocation. Results. There was a significantly lower incidence of PONV and PV in Groups A (PONV: 11.2%; PV: 3.2%) and B (PONV: 10.4%; PV: 3.2%) compared with Group C (PONV: 26.7%; PV: 13.3%), but there were no significant differences between Groups A and B. Conclusions. An inspired oxygen fraction of 0.8 does not further decrease PONV or vomiting in dolasetron-treated patients undergoing laparoscopic cholecystectomy. The lower incidence of PONV in Groups A and B compared with Group C is most likely caused by the omission of nitrous oxide.