Mild induced hypothermia and survival after out-of-hospital cardiac arrest.

BACKGROUND: Mild induced hypothermia (MIH) was introduced for post cardiac arrest care in Sweden in 2003, based on two clinical trials. This retrospective study evaluated its association with 30-day survival after out-of-hospital cardiac arrest (OHCA) in a Swedish community from 2003 to 2015.

METHODS: Out of 3680 patients with OHCA, 1100 were hospitalized after return of spontaneous circulation and 871 patients who remained unconscious were included in the analysis. Prehospital data were extracted from the Swedish Registry of Cardiopulmonary Resuscitation and in-hospital data were extracted from clinical records. Propensity score analysis on complete data sets and multivariable logistic regression with multiple imputations to compensate for missing data were performed.

RESULTS: Unadjusted 30-day survival was 23.5%; 37% in 386/871 (44%) MIH treated and 13% in 485/871 (56%) non-MIH treated patients. Unadjusted odds ratio (OR) for 30-day survival in patients treated with MIH compared to non-MIH treated patients was 3.79 (95% CI 2.71-5.29; p<0.0001). Using stratified propensity score analysis and in addition adjusting for in-hospital factors, 30-day survival was not significantly different in patients treated with MIH compared to non-MIH treated patients; OR 1.33 (95% CI 0.83-2.15; p=0.24). Using multiple imputations to handle missing data yielded a similar adjusted OR of 1.40 (95% CI 0.88-2.22; p=0.15). Good neurologic outcome at hospital discharge was seen in 82% of patients discharged alive.

CONCLUSION: Treatment with MIH was not significantly associated with increased 30-day survival in patients remaining unconscious after OHCA when adjusting for potential confounders.