Comparative Effectiveness of Therapeutic Hypothermia After Out-of-Hospital Cardiac Arrest: Insight from a Large Data Registry.

This study was done to determine the effectiveness of therapeutic hypothermia (TH) after out-of-hospital cardiac arrest (OHCA) among a large cohort of adults in the Cardiac Arrest Registry to Enhance Survival (CARES), with an emphasis on subgroups with a nonshockable first documented rhythm. This was an IRB approved retrospective cohort study. All adult index events at participating sites from November 2010 to December 2013 were study eligible. All patient data elements were provided. Summary statistics were calculated for all patients with and without TH. For multivariate adjustment, a multilevel (i.e., hierarchical), mixed-effects logistic regression (MLR) model was used with hospitals treated as random effects. Propensity score matching (PSM) on both shockable and nonshockable patients was done as a sensitivity analysis. After predefined exclusions, our final sample size was 6369 records for analysis: shockable=2992 (47.0%); asystole=1657 (26.0%); pulseless electrical activity=1249 (19.6%); other unspecified nonshockable=471 (7.4%). Unadjusted differences in neurological status at hospital discharge with and without TH were similar (p=0.295). After multivariate adjustment, TH had either no association with good neurological status at hospital discharge or that TH was actually associated with worse neurological outcome, particularly in patients with a nonshockable first documented rhythm (i.e., for NS patients, MLR odds ratio for TH=1.444; 95% CI [1.039, 2.006] p=0.029, and OR=1.017, p=0.927 via PSM). Highlighting our limitations, we conclude that when TH is indiscriminately provided to a large population of OHCA survivors with a nonshockable first documented rhythm, evidence for its effectiveness is diminished. We suggest more uniform and rigid guidelines for application.