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OOHCA: Hypothermia may improve outcome

Citation/s:  Hypothermia for neuroprotection after cardiac arrest: Systematic review and individual patient data meta-analysis, Critical Care Medicine 2005;33; 414-418.

Lead author's name and fax: Michael Holzer, Department of Emergency Medicine, General Hospital Vienna, Medical University of Vienna, Vienna, Austria

Three-part Clinical Question: Does induced mild hypothermia improve neurological recovery in survivors of primary cardiac arrest?

Search Terms: Hypothermia, Cardiac arrest, therapy

Data Sources: Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, non-English sources, CINAHL, PASCAL, BIOSIS

Study Selection: Included: randomized or quasi-randomized trials ^1-3, of adults, who were successfully resuscitated after primary out-of hospital cardiac arrest. Therapeutic hypothermia applied within 6 hours of arrival in A+E. Excluded: no control group or historical controls.    

Data Extraction: all authors of the identified trials supplied individual patient data with a pre-defined set of variables:

Patients: 3 studies enrolling 275, 77, & 33 patients, adults, comatose after VF/VF/PEA or asystole cardiac arrest, after return of spontaneous circulation

Treatment: induced hypothermia, target temperature < 35°C, 3 different methods (cooling mattress +/- icepacks, icepacks, helmet device), within 6 hours after arrival at Emergency Department after event

Outcome: Short term: good neurological recovery (Cerebral Performance Categories Scale 1 or 2) and discharge from hospital. Long term: good neurological recovery and alive at 6 months.

There were not multiple independent reviews of individual reports. They were not tested for heterogeneity.

The Evidence:

Comments:

1.      Do the methods allow accurate testing of the hypothesis?  No, the studies are heterogenous for patients included (VF/VT cardiac arrest versus PEA/asystole with known grim prognosis of the latter), of small sample size (n = 275, 77, & 33). Different methods of treatment in each trial (different method of cooling, target temperature, duration of hypothermia, method and timing of rewarming).   Different outcome measures and study objectives (one study³ was not designed to assess neurologic outcome, but to test the feasibility and timing of the helmet device to achieve hypothermia).

2.      Do the statistical tests correctly test the results to allow differentiation of statistically significant results? Yes, but note 1) and also outcome measure "alive at 6 months" was recorded in HACA trial only¹.

3.      Are the conclusions valid in view of the results? No. See Q1. There must be some doubt over the validity of the results due poor methodology.

4.      Did results get omitted, and why?    No, on the contrary: 3 patients who were not in the original publication in 2001 were added to Hachimi-Idrissi et al. for the purpose of this meta-analysis.

5.      Did the authors suggest areas of further research? Yes-further research necessary with standardised methodology and chosen end-points, to determine optimal method of cooling including duration, and to describe clearly long-term outcomes.

6.      Did they make any recommendations based on the results and were they appropriate? The authors suggest that mild hypothermia is effective in improving short-term recovery and survival in patients resuscitated from cardiac arrest of presumed cardiac origin. However further research regarding the exact method for applying hypothermia is recommended and a warning not to use hypothermia uncritically in view of possible adverse side effects is issued.

7.      Is the study relevant to my clinical practice?  Yes, but again, more due to the 2 large RCTs rather than this systematic review. Nothing new is added.

8.      Level of evidence? 1^- ; high risk of bias.

9.      What grade of recommendation does this study represent alone? N/A. 

10.  What grade of recommendation can I make when this study is considered along with other available evidence? B

11.  Should I change my practice in view of these results? Yes, but because of the 2 large RCTs.

12.  Should I audit my practice: if hypothermia used, then it should be audited with attention to clinical detail.
 

Appraised by:

Dr Anja G Beilharz, SHO, Stirling Royal Infirmary, Department of Anaesthesia, Intensive Care and Pain Management, Livilands Gate, Stirling FK8 2AU

15 June 2005.

Edited by CC & MD.
Email: anjagbeilharz@doctors.org.uk

Kill or Update By: May 2010

References:

1) HACA, NEJM, Feb 21, 2002, Vol.346: Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest

2) SA Bernard et al., NEJM, Feb 21, 2002, Vol.246 : Treatment of comatose survivors of out-of-hospital-cardiac arrest with induced hypothermia

3) S Hachimi-Idrissi et al., Resuscitation 51 (2001): Mild hypothermia induced by a helmet device: a clinical feasibility study

Citation: EBM Critical Appraisals. Scottish Intensive Care Society EBM Group. Beilharz AG. 2005 : Holzer M, et al. Hypothermia for neuroprotection after cardiac arrest: Systematic review and individual patient data meta-analysis, Critical Care Medicine 2005;33; 414-418.

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