LANCET, NOVEMBER 6, 1999
More Oxygen May Equal Less Postoperative Nausea
High oxygen concentrations during and after surgery can decrease postoperative nausea, report anaesthetists from Vienna, Austria, and San Francisco, CA, USA.
Studies in which nitrous oxide was omitted from anaesthetics and replaced by oxygen as a control have shown that oxygen itself may have anti-emetic properties, says first author Robert Greif. "This theory prompted us to try oxygen as an anti-emetic", he says.
In the trial, patients undergoing surgery received oral lormetazepam and ranitidine, followed by thiopentone, vecuronium, fentanyl, and isoflurane (09%). During surgery, and for 2 hours thereafter, patients received either 80% or 30% oxygen in nitrogen. Of 112 patients given 80% oxygen, 19 (17%) had nausea or vomiting, compared with 36 (30%) of 119 patients given 30% oxygen. No pulmonary atelectasis was detected clinically (Anesthesiol 1999; 91: 1246-52).
"Postoperative nausea and vomiting occurs frequently, and patients find it quite disturbing. It entails high costs in terms of anti-emetic drugs and hospital readmissions", says author Daniel Sessler. "The efficacy of supplemental oxygen, which is risk-free and inexpensive, is comparable to and may be better than serotonin antagonists." The mechanism of oxygen's anti-emetic action "is unknown, but it may be related to the prevention of intestinal ischaemia and the release of emetic factors", adds Greif.
When asked whether these results mark the departure of nitrous oxide from operating theatres, Martin Tramer (Geneva University, Switzerland) warned that "omitting nitrous oxide in general anaesthesia carries a risk of intraoperative awareness. In this study, oxygen had no effect on vomiting, only on nausea, and atelectasis was excluded only clinically, not by means of computed tomography".