Clinical paperDoes induction of hypothermia improve outcomes after in-hospital cardiac arrest?☆
Introduction
Hypothermia may reduce production of deleterious molecules, cerebral oxygen demand, and intracranial pressure in patients resuscitated from cardiac arrest, and thereby the final extent of their neurologic injury.1 Two trials showed hypothermia improved neurologic function versus normothermia in patients resuscitated from out-of-hospital ventricular fibrillation.2, 3
The burden of in-hospital4, 5 and out-of-hospital6 cardiac arrest are similar. While the physiology of brain injury is similar regardless of the location of arrest,7 patients resuscitated from in-hospital cardiac arrest (IHCA) are more likely than those resuscitated from out-of-hospital arrest to die with multiple organ failure.8 Thus, current care guidelines recommend induction of hypothermia after resuscitation regardless of the location of arrest.9 But no large observational study or trial has evaluated induced hypothermia in patients resuscitated from IHCA. We evaluated the effect of hypothermia in this population.
Section snippets
Methods
This study was approved by the Get With the Guidelines-Resuscitation (GWTG-R) scientific advisory board. The University of Washington Institutional Review Board (IRB) determined that this retrospective analysis of deidentified data was exempt from IRB review.
Study design
We used data from GWTG-R, an ongoing quality improvement project for IHCA. Participating hospitals voluntarily report data regarding in-hospital resuscitations as identified by an emergency resuscitation response by medical personnel and a resuscitation record. In GWTG-R, cardiac arrest is defined as patient unresponsiveness, apnea, and absence of a central pulse. The AHA provides quality control and oversight for all GWTG-R data collection, analysis, and reporting. Additional details regarding
Patient population
Included were adults who had IHCA between 2000 and 2009 in the general in-patient hospital ward and achieved restoration of spontaneous circulation. For an admission containing multiple cardiac arrest events, only the first arrest was included. Both primary and secondary analyses excluded patients who arrested in emergency departments, intensive care units, operating rooms, procedure areas, or post-procedural areas at the time of their arrest due to clinical circumstances associated with these
Exposure and outcomes
The primary exposure of interest was induced hypothermia after resuscitation. In GWTG-R, this was elicited as “Was induced hypothermia initiated after return of circulation … achieved?” without any specific definition of hypothermia. Sensitivity analyses cross-validated “induced hypothermia” by confirming that the lowest temperature in the first 24 h post event was ≤ 34 °C among patients treated between 2004 and 2009, when temperature data were included in GWTG-R.
The primary outcome was survival to
Data analysis
Baseline patient characteristics were summarized descriptively. The association between exposure and outcome was determined by covariate adjustment using propensity scores (PS).14, 15 This method uses logistic regression to predict the probability that an individual patient was exposed to the intervention of interest (e.g., hypothermia), with adjustment for factors recognized as potential confounders based on prior studies. The latter included: age, gender, race (white, black, other), prior
Results
10,860 patients were eligible for inclusion in the study (Fig. 1). 8316 (76.6%) patients from 454 hospitals had complete data and were used in the analysis. Patient demographics and clinical characteristics were summarized in Table 1. Patients had mean age of 67 years, and 52% had male gender. 73% were white, and less than 6% were Hispanic. The majority lived at home prior to the event, while only 8% resided in an acute care facility. 27% were monitored before the event, and 59% of events were
Discussion
In this retrospective analysis of patients with ICHA, only 2.6% of patients had hypothermia induced after resuscitation. A majority of treated patients were not documented as achieving the intended range of hypothermia or were overcooled. Induced hypothermia was not associated with survival or neurologic outcome.
Prior trials that reported benefit with induced hypothermia in patients resuscitated from cardiac arrest were conducted in different populations. The HACA trial included 275 comatose
Conclusion
Hypothermia is induced infrequently in patients resuscitated from IHCA. A minority of treated patients were reported as receiving hypothermia or achieving target temperatures. The observed absence of evidence of survival or neurological benefit in treated patients may be evidence of the absence of effect, or inefficient application of the intervention or residual confounding. Application of hypothermia should include monitoring of adherence to treatment targets. High-quality controlled studies
Conflict of interest statement
We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome beyond those stated below.
Nichol has applied for a grant from the National Heart Lung Blood Institute to conduct a randomized trial of different durations of induced hypothermia in patients resuscitated from out-of-hospital cardiac arrest, with third-party cost sharing to be provided by C.R.
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A Spanish translated version of the abstract of this article appears as Appendix in the final online version at http://dx.doi.org/10.1016/j.resuscitation.2012.12.009.