The Mölnlycke O.R. blog
Patient temperature management: When cool is the difference between life and death
The importance of maintaining a patient’s body temperature to as near normal (normothermia) as possible is something that we have heard a fair bit about on this blog (Patient warming: Prevention is better than cure) and elsewhere (e-Learning: Learn about inadvertent perioperative hypothermia and how to help prevent it) recently. Normothermia and its importance in helping to reduce surgical site infection (SSI) cannot be underestimated. But listening to and reading about all this got me thinking. What about those times when a patient is kept artificially cold? Why is this done and how was it even discovered? Finding out more about intentionally keeping patients cool (therapeutic hypothermia) was an interesting voyage.
Hypothermia has been applied therapeutically since antiquity. The Greek physician Hippocrates, the namesake of the Hippocratic Oath and arguably the world’s first modern doctor, advocated the packing of wounded soldiers in snow and ice. Napoleonic surgeon Baron Dominique Jean Larrey recorded that officers who were kept closer to the fire survived less often than the minimally pampered infantrymen. In modern times the first medical article concerning hypothermia was published in 1945. This study focused on the effects of hypothermia on patients suffering from severe head injury.
In the 1950s hypothermia received its first medical application, being used in intracerebral aneurysm surgery to create a bloodless field. Most of the early research focused on the applications of deep hypothermia, defined as a body temperature between 20–25°C (68–77°F). Such an extreme drop in body temperature brings with it a whole host of side effects, which made the use of deep hypothermia impractical in most clinical situations1.
This period also saw sporadic investigation of more mild forms of hypothermia, with mild hypothermia being defined as a body temperature between 32–34°C (90–93°F). Doctor Rosomoff demonstrated (in dogs) the positive effects of mild hypothermia after brain ischaemia and traumatic brain injury2. In the 1980s, further animal studies indicated the ability of mild hypothermia to act as a general neuroprotectant following a blockage of blood flow to the brain.
In 1999, following a skiing accident, Anna Bågenholm fell headlong into a river while skiing in northern Norway. Friends watched helplessly as Anna, a 29-year-old Swedish radiologist, was carried away by currents and finally wedged beneath thick ice floes. More than an hour passed before she was pulled to shore. By then, she had no heartbeat and her core temperature had plunged to 57°F/13.1°C. This would normally be referred to as “death”.
Emergency crews started cardiopulmonary resuscitation and kept at it during the hour-long flight to Tromsø University Hospital. It took nine hours of treatment and slow warming before Bågenholm came to, and she spent 60 days in intensive care. Yet she was back at work within five months, and a year later she was skiing again!
Bågenholm had not really died in the biological sense. Her heart had stopped, but like her other vital organs, including her brain, it was likely preserved by her extraordinarily low body temperature. Metabolism is governed in part by temperature, and as the body cools, its cells need less oxygen. At 57°F/13.1°C, with her metabolism slowed to just ten percent of its baseline rate, Bågenholm needed practically no oxygen at all. She was in a quasi-hibernating state of suspended animation, poised between life and death. Further to the animal studies and Anna Bågenholm's accident two landmark human studies were published simultaneously in 2002 by the New England Journal of Medicine3. Both studies, one occurring in Europe and the other in Australia, demonstrated the positive effects of mild hypothermia applied following cardiac arrest4. Responding to this research, in 2003 the American Heart Association (AHA) and the International Liaison Committee on Resuscitation (ILCOR) endorsed the use of therapeutic hypothermia following cardiac arrest2.
In its medical use, this deliberate super-cooling of the patient is called therapeutic hypothermia, or protective hypothermia. Lowering the patient's body temperature is done this way in order to help reduce the risk of the ischaemic injury to tissue following a period of insufficient blood flow3. Periods of insufficient blood flow may be due to cardiac arrest or the occlusion of an artery by an embolism, as occurs in the case of stroke. Therapeutic hypothermia may be induced by invasive means, in which a catheter is placed in the inferior vena cava via the femoral vein, or by non-invasive means, usually involving a chilled water blanket or torso vest and leg wraps in direct contact with the patient's skin. Studies have demonstrated that patients at risk for ischaemic brain injuries have better outcomes if treated with a hypothermia protocol4.
The types of medical events that may be treated effectively by these hypothermic therapies fall into five primary categories:
- hypothermia therapy for neonatal encephalopathy
- cardiac arrest
- ischaemic stroke
- traumatic brain or spinal cord injury without fever
- neurogenic fever following brain trauma
Whether the medical priority is maintaining normothermia or inducing hypothermia, it is clear that, given the stakes, managing a patient’s body temperature is critical.
- Polderman, Kees H. "Application of therapeutic hypothermia in the ICU." Intensive Care Med. (2004) 30:556-575
- Hypothermia After Cardiac Arrest: An Advisory Statement by the Advanced Life Support Task Force of the International Liaison Committee on Resuscitation - Nolan et al
- Ron Winslow (6 October 2009). "How Ice Can Save Your Life". Wall Street Journal. Retrieved 23rd September 2013
- Holzer, Michael. "Mild Hypothermia to Improve the Neurologic Outcome After Cardiac Arrest." New England Journal of Medicine. (2002) Vol. 346, No. 8