A Cochrane review included 6 studies and one abstract with a total of 1412 subjects assessing the effectiveness of therapeutic hypothermia in patients after cardiac arrest. When compared conventional cooling methods versus no cooling (four trials; 437 participants), it was found that participants in the conventional cooling group were more likely to reach a favourable neurological outcome (risk ratio (RR) 1.94, 95% confidence interval (CI) 1.18 to 3.21). Across all studies that used conventional cooling methods rather than no cooling (three studies; 383 participants), we found a 30% survival benefit (RR 1.32, 95% CI 1.10 to 1.65). Across all studies, the incidence of pneumonia (RR 1.15, 95% CI 1.02 to 1.30; two trials; 1205 participants) and hypokalaemia (RR 1.38, 95% CI 1.03 to 1.84; two trials; 975 participants) was slightly increased among participants receiving therapeutic hypothermia, and we observed no significant differences in reported adverse events between hypothermia and control groups.
A systematic review including 4 studies (RCTs or quasi-RCTs) with a total of 436 subjects was abstracted in DARE. Patients had primary cardiac arrest and were comatose (GCS<8) following return of spontaneous circulation. Studies that compared mild induced hypothermia (32 to 34ºC) with normothermia within 24 h of the patient's presentation were included. Cooling mattress (plus ice packs if required), ice packs and cooling helmet were used for cooling, the duration ranging from stopping after mild hypothermia was reached to 3 days. In 3 studies induction of mild hypothermia was associated with a significant reduction in in-hospital mortality compared with normothermia (RR 0.75, 95% CI 0.62 to 0.92, NNT for preventing one in-hospital death = 7). In 4 studies induction of mild hypothermia was associated with a significantly reduced risk of poor neurological outcome compared with normothermia (RR 0.74, 95% CI 0.62 to 0.84, NNT for preventing one poor neurological outcome = 5, 95% CI 4 to 10). Treatment-limiting adverse events were not consistently reported. There were no statistically significant differences in adverse events between mild hypothermia and normothermia.