Therapeutic Hypothermia: An old treatment gets a new look

Imagine you are on a suburban paramedic crew that responds to a 60-year-old woman who collapsed in front of her husband as she attempted to get out of bed to use the bathroom. Telephone CPR is in progress. On arrival, you find the patient in v-fib. You administer three shocks, and your partner begins intubating the patient. Eventually, you’re able to get back a working rhythm. Sounds pretty routine so far, but here’s where it gets interesting: En route to the hospital, as part of your local protocol, you begin an infusion of ice-cold saline. Sound strange? Perhaps not.

Clinical use of therapeutic hypothermia has been around for over 70 years. After waxing and waning in popularity, therapeutic hypothermia has reemerged as a potentially lifesaving tool in the fight to save the hypoxic brain. Although there is a growing body of evidence to support this treatment, further research on therapeutic hypothermia is needed to see if this treatment option should become the new standard of care.

Emergency medical services have gone through dramatic changes in the last 25 years. Cutting-edge drugs and diagnostic equipment give patients the best possible chance of survival, especially when it comes to out-of-hospital cardiac arrests. Despite these advances, however, the statistical chance of a patient making full neurological recovery following an out-of-hospital cardiac arrest is still very poor. The medical community needs to consider how to help these patients not only survive, but have a quality life. Further research on therapeutic hypothermia, a relatively new treatment that may increase the odds of neurological recovery, may be the answer. A coordinated effort between EMS and hospitals to research the use of therapeutic hypothermia to treat cardiac arrests should be explored.

History

It is well known that the brain responds poorly to hypoxic events. In most situations, the 4–6-minute “point of no return” still applies. Part of the problem (perhaps not realized by many responders) is that brain damage will continue for several hours following resuscitation; it doesn’t simply stop because the patient’s heart starts beating again.1 In fact, only a fraction of cardiac arrest patients fully recover from this brain damage. One study showed that while 17%–25% of cardiac arrest patients survived to hospital admission, only 4%–9% left the hospital neurologically intact.2 Some research has shown, however, that therapeutic hypothermia can help increase the odds of these patients recovering completely.

Medical application for hypothermia actually began thousands of years ago with the ancient Egyptians, Greeks and Romans.3 Even then, practitioners recognized that hypothermia could slow bleeding. Anecdotal evidence of the therapeutic effects of hypothermia can also be seen in children who drown in an ice-covered lake, only to be revived 30 minutes later without brain damage.

The mechanism of how hypothermia protects brain tissue is not clearly understood and is beyond the scope of this article. Suffice it to say that hypothermia is believed to decrease cerebral oxygen requirements and reduce the production of free radicals that can cause permanent brain damage.4

Clinicians began seriously exploring medical use of induced hypothermia in the 1930s, when cases were published citing favorable outcomes in patients resuscitated after long periods of apnea following cold-water drowning.3 Animal studies subsequently carried out in the 1950s were able to show a benefit from induced hypothermia in dogs with brain trauma and ischemia. These early studies led to human trials in the 1960s, but the human experiments were largely abandoned due to serious complications and difficulty in proving efficacy.3 The complications were serious enough to stall further therapeutic hypothermia research for decades. A review of severe hypothermia side effects includes: