Nine studies were included in the total i.v. anaesthetic meta-analysis. Other meta-analyses are described elsewhere (see Other Publications of Related Interest).
All interventions assessed appear to reduce early (<6 hours) post-operative nausea and vomiting. Control conditions showed 20-60% early and 40-80% late emetic event rates.
For early emetic events, Propofol anaesthesia decreased the incidence of nausea and vomiting: NNT (nausea and vomiting) = 4.9; 95% CI: 3.7 to 7.1.
Omitting nitrous oxide decreased vomiting but not nausea: NNT (nausea) =9.1; 95% CI: 4.1 to (; NNT (vomiting) = 4.8; 95% CI: 3.6 to 7.3.
Total i.v. anaesthesia with propofol also appeared effective for reducing early events, but these studies were small and poorly-reported. NNT (nausea) = 5.6; 95% CI: 3.4 to 16; NNT (vomiting) = 3.3; 95% CI: 2.3 to 5.4.
The 95% confidence intervals of the NNT for all these interventions overlapped: there was no significant difference between them.
Both propofol maintenance and omitting nitrous oxide reduced late vomiting, with NNTs of 6.3 (95% CI: 3.6 to 27) and 5.6 (95% CI: 3.9 to 10) respectively. Propofol also reduced late nausea: NNT =2.8, 95% CI 1.8 to 6.8, but again, omitting nitrous oxide did not affect nausea. The data on total i.v. anaesthesia were insufficient to permit any conclusions to be drawn on late efficacy.