Abstract: We included 23 studies with 1250 participants that compared one drug with one or more other drugs. Of these comparisons, 19 studies compared propofol with another drug. Seven of these compared propofol with etomidate (four of which combined the drugs with remifentanil or fentanyl), five midazolam, six thiopentone and two sevoflurane. Three studies compared etomidate with thiopentone, and three etomidate with midazolam. Two studies compared thiopentone with midazolam, one thiopentone with diazepam and one midazolam with diazepam. Drug doses and the time over which the drugs were given varied between studies. Although all studies were described as randomized, limited information was provided about the methods used for selection and group allocation. A high level of performance bias was observed across studies, as study authors had not attempted to blind the anaesthetist to group allocation. Similarly, study authors had rarely provided sufficient information on whether outcome assessors had been blinded. Included studies presented outcome data for hypotension, apnoea, participant recall, success of cardioversion, minor adverse events of nausea and vomiting, pain at injection site and myoclonus, additional analgesia and participant satisfaction. We did not pool the data from different studies in view of the multiple drug comparisons, differences in definitions and reporting of outcomes, variability of endpoints and high or unclear risk of bias across studies. Few studies reported statistically significant results for our relevant outcomes, and most study authors concluded that both, or all, agents compared in individual studies were adequate for cardioversion procedures. It is our opinion that at present, there is no evidence to suggest that current anaesthetic practice for cardioversion should change.

Plain-language summary: Evidence is current to 27 March 2014. We found 23 relevant randomized controlled trials with 1250 participants undergoing cardioversion procedures. These studies compared one anaesthetic drug against one or more other drugs, including propofol, etomidate, thiopentone, sevoflurane, midazolam and diazepam. Study authors considered clinical outcomes such as decreased blood pressure, interrupted breathing and whether cardioversion was successful, as well as patient relevant outcomes such as recall, nausea and vomiting, pain on injection and satisfaction with the procedures. In addition to a variety of drug comparisons between studies, differences in study methods were described, with drugs given in different doses and over different lengths of time. These differences meant that it was inappropriate to combine the results of these studies. We believe that the quality of these studies was not sufficiently high, and that it would be misleading to combine the findings of all studies within this review. Study authors had not taken enough steps to reduce the risk of differences in methods within the studies, for example, by masking doctors and assessors regarding which drug was given to each patient. Most authors of individual studies concluded that all agents studied were adequate for making patients unaware during cardioversion. It is our opinion that at present, there is no evidence to suggest that drugs used by anaesthetists to make patients unaware of cardioversion should change.