How Therapeutic Hypothermia Works

Chilled to Perfection
You can get a better idea of what a patient receiving therapeutic hypothermia might look like in this picture.
You can get a better idea of what a patient receiving therapeutic hypothermia might look like in this picture.
© Tim Shaffer/Reuters/Corbis

Therapeutic hypothermia requires balancing a ticking clock against the limits of how fast a body can be safely cooled or warmed. During the procedure, a patient is brought to target temperature quickly, kept in the desired range without fluctuations, and rewarmed slowly and steadily. These three steps define the three phases of therapeutic hypothermia: induction, maintenance and rewarming. Although the ideal duration of hypothermia remains unknown, the standard procedure lasts no more than 24 hours [sources: Adler at al.; Deckard and Ebright].

To prepare the patient for cooling, doctors increase sedation and watch for shivering. Shivering, the body's attempt to maintain its proper temperature, bumps up metabolic activity, increases oxygen consumption and raises body heat, so doctors block it with a paralytic [source: Deckard and Ebright].

Throughout the process, doctors may use one of several cooling technologies. During the cooling phase, ice packs placed around the armpits, chest, groin and sides of neck offer an inexpensive solution, but can cause undesirable high and low temperatures and require a lot of attention [sources: Adler at al.; Deckard and Ebright; Gibson and Andrews]. More invasive options, such as rapid intravenous infusions of chilled saline solution or cooling catheters, offer better temperature control but bring risks of their own[sources: Deckard and Ebright; Gibson and Andrews].

If the induction stage is not properly handled, patients can develop arrhythmias, including bradycardia (very slow heart rate), atrioventricular blocks (lags in the electrical signal between the atria and ventricles), and atrial and ventricular fibrillation [source: Deckard and Ebright].

During the maintenance phase, cooling might be handled noninvasively, by sandwiching the patient between special cold-water or cold-forced-air blankets, or wrapping their trunk, back and thighs in hydrogel-coated pads that circulate temperature-controlled water. Doctors might also continue core cooling using a catheter [source: Adler at al.; Deckard and Ebright; Gibson and Andrews; Resuscitation Central].

This phase, too, runs the risk of arrhythmias if not properly handled. The problem involves electrolytes (potassium, magnesium, calcium and phosphate), which move into and out of cells during temperature shifts and create harmful imbalances. Doctors handle this problem through electrolyte replacement and careful monitoring during the maintenance phase [sources: Deckard and Ebright; Delfin; Kupchik].

During rewarming, the patient's temperature is raised at a crawl -- around 0.27 to 0.90 F (0.15 to 0.50 C) per hour [sources: Adler at al.; Deckard and Ebright]. If employing cooling pads, doctors can gradually bump up the water temperature within until body temperature hovers at low normothermia for one hour. During or shortly after this period, depending on methods used, doctors will discontinue the paralytic and sedative drugs [source: Adler at al.]

In all phases, staff carefully monitors core body temperature, fluid levels and other key indicators. Afterward, recovery requires extensive nursing and management care in an intensive care unit (ICU). Just how long varies, but expect a stay of around four days to a week [source: Delfin].

In other words, therapeutic hypothermia is neither simple nor cheap, but, with luck, it will be one icy reception you will be grateful to have received [sources: Adler at al.; Deckard and Ebright].

Author's Note: How Therapeutic Hypothermia Works

The subject of therapeutic hypothermia is one close to my heart. Back in the early 1960s, a close family member was saved from cerebral hemorrhage by being "put on ice" by specialists at a local research hospital. It was early days for such treatments, and intervention was late in coming. Indeed, the doctors at the time gave the patient very poor odds, on the order of 1 in 10,000 against survival. Thanks to therapeutic hypothermia, he beat those odds and is still with us today.

Related Articles

More Great Links


  • Adler, Jonathan, et al. "Therapeutic Hypothermia." April 30, 2014. (Feb. 23, 2015)
  • Andrews, Peter. Consultant in Anesthetics & Critical Care, NHS Lothian. Personal correspondence, Feb. 24, 2015.
  • Columbia University Department of Neurological Surgery. "Cerebral Ischemia." (Feb. 18, 2105)
  • Davis, Charles P. "Hypothermia." eMedicine Health. Dec. 17, 2014. (March 1, 2015)
  • Deckard, Michelle E. and Patricia R. Ebright. "Therapeutic Hypothermia After Cardiac Arrest: What, Why, Who, and How." American Nurse Today. Vol. 6, no. 7. July 2011. (Feb. 19, 2015)
  • Delfin, Gail MSN RN, Nurse Researcher at the Center for Resuscitation Science, University of Pennsylvania. Personal correspondence. Feb. 27, 2015.
  • Encyclopedia Britannica. "Hypothermia." (Feb. 18, 2015)
  • Gibson, Alistair and Peter J. D. Andrews. "Therapeutic Hypothermia, Still 'Too Cool to Be True?'" F1000Prime Reports, Vol. 5, no. 26. July 2013. (Feb. 19, 2015)
  • Hsia, CCW, et al. "Evolution of Air Breathing: Oxygen Homeostasis and the Transitions from Water to Land and Sky." Comprehensive Physiology. Vol. 3, no. 2. Page 849. 2013. (March 1, 2015)
  • Kupchik, Nicole L. "Development and Implementation of a Therapeutic Hypothermia Protocol. Critical Care Medicine." Vol. 37, no. 7. Page S279. 2009. (Feb. 23, 2015)
  • Lai, Ming-Chi and San-Nan Yang. "Perinatal Hypoxic-Ischemic Encephalopathy." Journal of Biomedicine and Biotechnology. 2011. (Feb. 27, 2015)
  • Leary, Marion MPH MSN RN, Assistant Director of Clinical Research at the Center for Resuscitation Science, University of Pennsylvania. Personal correspondence. Feb. 27, 2015.
  • Meek, Leslie R. "Neuron Lectures." (March 1, 2015)
  • The Merck Manual. "Cardiac Arrest." February 2013. (Feb. 20, 2015)
  • Merriam-Webster. "Ischemia." (Feb. 18, 2105)
  • Mosby's Medical Dictionary, 8th ed. "Cerebral Perfusion Pressure." (Feb. 20, 2015)
  • Murphy, Kate. "Killing a Patient to Save His Life." The New York Times. June 9, 2014. (Feb. 18, 2105)
  • National Heart, Lung, and Blood Institute. "What to Expect During Heart Surgery." National Institutes of Health. Nov. 8, 2013. (Feb. 20, 2015)
  • Nolan, J.P., et al. "Therapeutic Hypothermia After Cardiac Arrest." Circulation. Vol. 108. Page 118. 2003. (Feb. 18, 2105)
  • Resuscitation Central. "Cooling Techniques." 2010. (Feb. 23, 2015)
  • Texas Heart Institute. "A Heart Surgery Overview." August 2014. (Feb. 18, 2105)
  • Winslow, Ron. "How Ice Can Save Your Life." The Wall Street Journal. Oct. 6, 2009. (Feb. 23, 2015)
  • Ziganshin, Bulat A. and John A. Elefteriades. "Deep Hypothermic Circulatory Arrest." Annals of Cardiothoracic Surgery. Vol. 2, no. 3. Page 303. May 2013. (Feb. 18, 2105)