Data

Though physicians as early as Hippocrates recognized the benefits of therapeutic hypothermia in attenuating injury, only more recently has the evidence in favor of its use in cardiac arrest begun to warrant its use.⁷ Several authorities have endorsed the use of therapeutic hypothermia in eligible patients (see next section), including the International Liaison Committee on Resuscitation, the AHA, and the European Resuscitation Council.

Formal studies as early as the 1950s began to demonstrate the benefits of hypothermia after cardiac arrest. For instance, a study by Benson et al. in 1959 of 19 patients showed that 6 of 12 patients who were cooled to a target of 31-32°C survived after cardiac arrest, compared with only 1 of 7 in the uncooled group.⁸

More recently, two landmark randomized, controlled trials – one done in Australia and one in Europe – were published in the New England Journal of Medicine in 2002 showing that therapeutic hypothermia has neuroprotective effects after resuscitation from cardiac arrest. In the Australian trial by Bernard et al., 77 comatose survivors of cardiac arrest were randomized to hypothermia (treatment) vs. normothermia (control) groups. They found that 49% of the 43 patients treated with therapeutic hypothermia survived with favorable neurologic outcomes, compared with just 26% of the 34 normothermia group (P = .05).⁹

In the European multicenter trial by the Hypothermia After Cardiac Arrest Study Group, 275 comatose survivors were randomized to treatment (N = 136) and control (N = 137) groups. In the hypothermia group, 55% had a favorable neurologic outcome 6 months later, compared with 39% in the control group (P = .009). Therapeutic hypothermia significantly improved functional recovery at hospital discharge (55% vs. 39%, number needed to treat [NNT] = 6) and improved 6-month mortality rate, compared with the control, noncooled group (41% vs. 55%, NNT = 7).¹⁰

The numbers needed to treat before seeing a benefit from therapeutic hypothermia are remarkably low, approaching those seen with other important therapeutic interventions, such as percutaneous coronary intervention.

More data are emerging for the use of therapeutic hypothermia in post–cardiac arrest patients and numerous other conditions, including traumatic brain injury, hemorrhagic shock, and even neonatal hypoxic encephalopathy. Currently, at least 19 clinical trials are ongoing to further investigate the benefits of therapeutic hypothermia on ROSC and other conditions.

Who Is Eligible?

To be eligible for therapeutic hypothermia, patients must meet all of the following criteria: