Influence of mild therapeutic hypothermia after cardiac arrest on hospital mortality

Abstract

Objective: Following two randomized controlled trials that demonstrated reduced mortality and better neurological outcome in cardiac arrest patients, mild therapeutic hypothermia was implemented in many intensive care units. Up to now, no large observational studies have confirmed the beneficial effects of mild therapeutic hypothermia.

Design: Internet-based survey combined with a retrospective, observational study.

Patients: All patients admitted to an intensive care unit in The Netherlands after cardiac arrest from January 1, 1999 until January 1, 2009.

Data source: Dutch National Intensive Care Evaluation database.

Methods: The moment of implementation of mild therapeutic hypothermia for each hospital participating in the Dutch National Intensive Care Evaluation database was determined with an Internet survey. To compare mortality before and after implementation of mild therapeutic hypothermia, the odds ratio adjusted for Simplified Acute Physiology Score II score, age, gender, propensity score, and in- or out-of-hospital cardiac arrest was calculated. Patients were excluded if 1) they were admitted to an intensive care unit that did not respond to the survey, 2) they were admitted within 3 months after implementation of mild therapeutic hypothermia, 3) they had a Glasgow Coma Scale score of >8, or 4) they did not satisfy the Simplified Acute Physiology Score II inclusion criteria.

Interventions: None.

Measurements and main results: A total of 13,962 patients were admitted to an intensive care unit following cardiac arrest. In total 8,645 patients were excluded, 5,544 because of a Glasgow Coma Scale score of >8. Of the resultant 5,317 patients, 1,547 patients were treated before and 3,770 patients after implementation of mild therapeutic hypothermia. Patients admitted after implementation of mild therapeutic hypothermia had lower minimal and maximal temperatures (p < .0001) during the first 24 hrs on the intensive care unit compared to patients admitted before implementation of mild therapeutic hypothermia. The adjusted odds ratio of the hospital mortality of patients treated after implementation of mild therapeutic hypothermia was 0.80 (95% confidence interval of 0.65-0.98, p = .029).

Conclusion: The results of this retrospective, observational survey suggest that implementation of mild therapeutic hypothermia in Dutch intensive care units is associated with a 20% relative reduction of hospital mortality in cardiac arrest patients.