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Therapeutic hypothermia after cardiac arrest: Unintentional overcooling is common using ice packs and conventional cooling blankets

Merchant, Raina M. MD; Abella, Benjamin S. MD, MPhil; Peberdy, Mary Ann MD; Soar, Jasmeet MD; Ong, Marcus E. H. MBBS, MPH; Schmidt, Gregory A. MD; Becker, Lance B. MD; Vanden Hoek, Terry L. MD

doi: 10.1097/01.CCM.0000246016.28679.36
Scientific Reviews

Objectives: Although therapeutic hypothermia for cardiac arrest survivors has been shown to improve neurologically intact survival, optimal methods to ensure controlled induction and maintenance of cooling are not clearly established. Precise temperature control is important to evaluate because unintentional overcooling below the consensus target range of 32–34°C may place the patient at risk for serious complications. We sought to measure the prevalence of overcooling (<32°C) in postarrest survivors receiving primarily noninvasive cooling.

Design: Retrospective chart review of postarrest patients.

Setting: Three large teaching hospitals.

Patients: Cardiac arrest survivors receiving therapeutic hypothermia.

Interventions: Charts were reviewed if primarily surface cooling was used with a target temperature goal between 32°C and 34°C.

Measurements and Main Results: Of the 32 cases reviewed, overcooling lasting for >1 hr was identified as follows: 20 of 32 patients (63%) reached temperatures of <32°C, 9 of 32 (28%) reached temperatures of <31°C, and 4 of 32 (13%) reached temperatures of <30°C. Of those with overcooling of <32°C, 6 of 20 (30%) survived to hospital discharge, whereas of those without overcooling, 7 of 12 (58%) survived to hospital discharge (p = not significant).

Conclusions: The majority of the cases reviewed demonstrated unintentional overcooling below target temperature. Improved mechanisms for temperature control are required to prevent potentially deleterious complications of more profound hypothermia.

From the Sections of Emergency Medicine (RMM, LBB, TLVH) and Pulmonary and Critical Care (GAS), University of Chicago Hospitals Emergency Resuscitation Center, Chicago, IL; the Department of Emergency Medicine, Virginia Commonwealth University Health System, Richmond, VA (MAP, MEHO); the Department of Anesthesia and Intensive Care Medicine, Southmead Hospital North Bristol NHS Trust, Bristol, UK (JS); and the Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA (BSA). Dr. Abella has received research funding from the National Heart, Lung and Blood Institute, Philips Medical Systems, and Laerdal Medical Corp. and has received speaking honoraria from Alsius Corp., Philips Medical Systems, and Laerdal Medical Corp. Dr. Becker has received grants or research support from National Institutes of Health (NIH), Philips Medical Systems, Laerdal Medical Corp., and Alsius Corp. He is a consultant for Abbott Laboratories and Philips Medical Systems; holds patents (issued and pending) on hypothermia induction devices and methods; is inventor and equity partner in Cold Core Therapeutics LLC; and is a special government employee on the Food and Drug Administration CPR Device Panel. For the American Heart Association (AHA), he is past chair of the Cardiopulmonary, Perioperative, and Critical Care Council, a member of the Basic Life Support Subcommittee, chair of the Research Working Group on Emergency Cardiovascular Care, and director of the Resuscitation Science Symposium 2005. Dr. Vanden Hoek has received grants or research support from the NIH and Department of Defense, Office of Naval Research; holds patents (issued and pending) on hypothermia induction devices and methods; is inventor and equity partner in Cold Core Therapeutics LLC. For the AHA, he is current chair of the ACLS Committee and member of the Airway Task Force. The remaining authors have not disclosed any potential conflicts.

Supported, in part, by the University of Chicago Emergency Resuscitation Center, Chicago, IL, and Philips Medical Services Fellowship Training Grant, Seattle, WA.

© 2006 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins