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Etomidate is a widely used hypnotic drug for induction of general anesthesia and sedation, especially in elderly patients and hemodynamically unstable patients. Myoclonus, however, is the most prominent problem during induction of anesthesia with etomidate. Many agents have been used to prevent it and opioid is one of them. This meta-analysis was to evaluate effects of opioids pretreatment for preventing etomidate-induced myoclonus. We searched the PubMed, EMBASE, and the Cochrane Library databases and published studies in English updated to September 2015. Randomized controlled trials of opioids versus placebo/control in patients were included. We evaluated the prophylactic effect of opioids on etomidate-induced myoclonus. All statistical analysis was performed using RevMan 5.2 software. Nine randomized controlled trials involving 604 participants were included. The results indicated that compared with placebo/control, opioids allow more patients to experience no myoclonic movements after etomidate injection [risk ratio (RR) 2.76, 95% confidence interval (CI) 1.75–4.37, P < 0.0001]. The numbers of patients with mild myoclonus [(RR) 0.53, 95% (CI) 0.36–0.78, P = 0.001], moderate myoclonus [(RR) 0.36, 95% (CI) 0.23–0.55, P < 0.00001], and severe myoclonus [(RR) 0.20, 95% (CI) 0.08–0.52, P = 0.0009] after etomidate injection were significantly decreased with the pretreatment of opioids. This meta-analysis suggests that pretreatment with opioids before injecting etomidate was effective for preventing etomidate-induced myoclonus and can reduce the intensity of myoclonus without any adverse effects.