Background:

Recent studies indicate that aggressive hypothermia for out-of-hospital cardiac arrest (OHCA) may be unnecessary. This has raised skepticism regarding the utility of hypothermia for OHCA. The aim of this meta-analysis was to determine whether hypothermia improves clinically-relevant outcomes compared with normothermia, and whether outcomes are dependent on target temperature for OHCA patients.

Methods:

A comprehensive search was undertaken to identify all randomized trials (RCTs) of lower versus higher temperature for OHCA patients (defined as hypothermia versus normothermia for the primary analysis, and redefined as <36°C versus ≥36°C for the secondary analysis). MEDLINE, Cochrane, and EMBASE were searched to July 2014. The primary outcome was a composite of death or poor neurologic outcome defined as cerebral performance category (CPC) score over 2. Risk ratios (RR) and 95% confidence intervals [CI] were calculated, and meta-regression was performed by temperature achieved. Heterogeneity was calculated using I² statistic.

Results:

For normothermia versus hypothermia, 7 RCTs involving 570 patients were included. For <36°C versus ≥36°C, 8 RCTs involving 1509 patients were included. Hypothermia versus normothermia significantly reduced the composite of death/poor neurologic outcome (RR 0.79, 95% CI 0.68 to 0.92, p=0.002; I²=40%). In addition, all-cause mortality (RR 0.79, 95%CI 0.67 to 0.92; p=0.003; I²=0%) was reduced and good neurologic outcome of CPC 1 or 2 (RR 1.42, 95%CI 1.15 to 1.74; p=0.001, I²=4%) was significantly improved with hypothermia. Results were similar in the secondary analysis of lower versus higher temperature (ie, for <36°C versus ≥36°C). Meta-regression showed a significant relationship between target temperature and death/poor neurologic outcome (p<0.0001).

Conclusion:

Existing evidence indicates that lower temperatures improve all-cause mortality and neurologic outcomes compared with higher temperatures in OHCA, and meta-regression suggests that lower temperatures are associated with the greatest improvement.

Footnotes