Efficacious and safe treatment strategies for patients who are nauseated or who are vomiting after surgery are needed. The aim of this study was to systematically review the literature on valid data on any treatment of established PONV symptoms, to critically appraise the data, to test for dose-responsiveness for each drug, and to estimate relative efficacy and likelihood for harm of the various treatments.
We searched the MEDLINE (PubMed, from 1966), and EMBASE (from 1974) databases using different search strategies. We also searched the Cochrane Controlled Trials Register (Cochrane Library 2000, issue IV). We used the free text terms (postoperative OR postoperative OR postsurg*), (nausea OR vomiting OR emesis OR retching), (randomised OR randomized), (treatment), NOT (chemotherapy OR radiotherapy), NOT (prevention OR prophylaxis) and combinations of these terms. The date of the last electronic search was 21.8.2000. We checked reference lists of retrieved reports and relevant review articles, and we searched our own comprehensive in-house bibliography. Authors of original trials were contacted when there was ambiguity about the data. We did not contact manufacturers.
We included full reports of randomised comparisons of any therapeutic antiemetic intervention (experimental intervention) with placebo, no treatment or another antiemetic (control intervention) in vomiting or nauseated postoperative patients. When Intralipid® was used as a control in propofol trials (to maintain blinding due to its milky-white colour), it was considered as an inactive control.
Retrieved reports were screened by one author (FK). Reports, which did not clearly meet inclusion criteria were excluded at this stage. All potentially relevant reports were then read by all authors independently who scored them for methodological validity using the three-item, five point Oxford scale taking into account randomisation, double-blinding, and description of withdrawals [7]. The minimum validity requirement for an included trial was an adequate method of randomisation (for instance, a table of random numbers). Trials with pseudorandomisation (for instance, according to patients' date of birth) were excluded.
The main endpoint of efficacy was a "success" (i.e. no further nausea or vomiting in a nauseated or vomiting patient). According to previous analyses [8], and in agreement with the majority of all retrieved trials, we distinguished between two arbitrarily defined observations periods: "early success" was within or close to 6 hours after administration of the study drugs, and "late success" was within or close to 24 hours. Dichotomous data on anti-vomiting and anti-nausea efficacy were separately extracted, and separately analysed. When no distinction was made between nausea and vomiting, the data were not further analysed. Data on adverse drug reactions were analysed when they were reported in dichotomous form. Data on patients' satisfaction, duration of hospital stay, number of vomiting episodes, degree of nausea, or number of rescue treatments were not analysed since these data were inconsistently reported. Sponsorship was assumed when it was acknowledged in the original paper or when a representative of the manufacturer was a co-author of the paper. All data were extracted by one author (FK) and then checked by the two others independently. Authors met to agree consensus on validity scores and extracted data; discrepancies were resolved by discussion.
For both efficacy and harm we calculated relative risks with 95% confidence intervals [9]. A statistically significant difference between an experimental intervention and control was assumed when the 95% confidence interval around the relative risk did not include 1. Data from independent trials were combined only when the data represented clinically homogenous subgroups. Such subgroups would include comparisons of data of the same dose and route of administration of the same experimental intervention, with the same control intervention (for instance, a placebo), and reporting on the same emesis endpoint (for instance vomiting) during the same observation period (for instance late success). A fixed effect model was used to combine these clinically homogenous data [10].
It became clear that valid trials represented homogenous patient populations with minimal variations in baseline risks and outcome frequencies. Also, most antiemetic interventions were tested in one or two large multicentre studies with similar control event rates. As estimates of the clinical relevance of the antiemetic efficacy
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