Six RCTs were eligible including 4,745 patients (range 40 to 2,894). Studies had a low risk of bias for all domains, except for one study with an unclear risk of detection bias, and a different study having an unclear risk of attrition bias.
There were no significant differences between groups for overall rates of sustained restoration of spontaneous circulation, long-term survival or favourable neurological outcome.
In the subgroup analyses, for patients in asystole, vasopressin treatment was associated with higher long-term survival (OR 1.80, 95% CI 1.04 to 3.12, Ι²=9%; five RCTs). In asystolic patients of trials with mean time from cardiovascular collapse to first study-drug injection being less than 20 minutes, vasopressin increased the rates of sustained restoration of spontaneous circulation (OR 1.70, 95% CI 1.17 to 2.47, Ι²=0%; two RCTs) and long-term survival (OR 2.84, 95% CI 1.19 to 6.79, Ι²=17%; three RCTs).
Sensitivity analysis results were similar to the primary analysis results.