Brain Cooling for Brain Injury

Research suggests hypothermia therapy may not benefit children with brain injuries. In June, Reuters reported that "chilling the body to well below its normal temperature does little to protect children from further damage after an accidental brain injury, and may even make things worse," according to a study published in the June 5 issue of the New England Journal of Medicine. The original article is "Hypothermia Therapy after Traumatic Brain Injury in Children" by James S. Hutchison, M.D. and his colleagues for the Hypothermia Pediatric Head Injury Trial Investigators and the Canadian Critical Care Trials Group (N Engl J Med 2008;358:2447-56).

This was a multicenter, international trial in which researchers enrolled 225 children (mean age of 10) who were admitted with acute brain injury to pediatric intensive care units in 17 centers. The investigators randomized 108 children to hypothermia therapy -- cooling to about 32.5° C -- initiated within eight hours of the injury and maintained for 24 hours and 117 children to normothermia -- about 37° C. The researchers found that at six months post-injury, 31 percent of children given hypothermia therapy had a severe disability, were in a persistent vegetative state, or had died, compared with 22 percent of patients who were not cooled. Although a greater proportion (21 percent) of patients died in the hypothermia group than in the control group (12 percent), the difference fell short of statistical significance. The conclusions noted in the original article were that "in children with severe traumatic brain injury, hypothermia therapy that is initiated within 8 hours after injury and continued for 24 hours does not improve the neurologic outcome and may increase mortality."

This is a bit of a surprising finding, in part because animal (rodent) studies have been encouraging. However, as we have learned from many other therapeutic issues (e.g., cancer therapy), the translation from animal models to humans is not always guaranteed, which is why clinical investigations are performed in humans. The underlying premise of using hypothermia for acute brain injury is that by cooling the brain, its metabolic rate will slow and therefore it will tolerate an episode of low oxygen, low blood flow (perhaps due to brain swelling), and the provision of diminished energy resources (also perhaps due to brain swelling).

Can these results be extrapolated to other situations that involve the brain for which controlled hypothermia is sometimes recommended, such as a drowning episode, or for which it is not currently recommended, such as high altitude cerebral edema? We do not know.

The current dictum for victims of accidental hypothermia is that their brains may be protected by the low temperature, so that a resuscitation may be carried out differently (e.g., fewer chest compressions and rescue breaths per minute) than would be a resuscitation under a condition of normal body temperature. This has never been precisely studied, but is a generally accepted notion. Whether or not this study of traumatized brains in children might cast doubt upon that notion remains to be seen, because in hypothermia victims who survive neurologically intact, there is no underlying structural brain injury.

image courtesy of www.medicineworld.org

Tags: hypothermia, brain injury, traumatic brain injury, wilderness medicine, outdoor medicine, healthline

Labels: brain injury, children, hypothermia, trauma

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