Sudden cardiac death claims more than 350,000 victims in the United States every year.1 The mortality rate for out-of-hospital cardiac arrest remains a staggering 65% to 95%, with only 10% to 20% of survivors discharged from the hospital with a good neurologic outcome.2 Therapeutic hypothermia for the treatment of comatose survivors of cardiac arrest is a proven therapy to improve survival and neurologic outcome.3-5
Many consider therapeutic hypothermia to be a relatively new concept. Experiments with deep therapeutic hypothermia began in the 1940s with initially mixed results. In the 1950s, studies examined moderate hypothermia in the range of 26°C to 32°C (i.e., 78.8°F to 89.6°F) in comatose survivors of cardiac arrest and reported a trend toward improved outcomes but were complicated by difficult-to-control side effects. Additional animal studies of mild hypothermia in the range of 32°C to 35°C (i.e., 89.6°F to 95°F) in the 1980s and small clinical trials in the 1990s demonstrated that even mild hypothermia provided protective benefits with far fewer side effects.2
Two landmark randomized trials published in 2002 specifically examined the use of mild hypothermia in comatose survivors of witnessed cardiac arrests with initial rhythms of pulseless ventricular tachycardia or ventricular fibrillation.6,7 Meta-analyses report that only seven patients need to be treated to save one life and only five patients need to be treated to prevent one poor neurologic outcome.8,9 Utilizing strict screening criteria of these studies resulted in only 10% of screened patients being eligible. Follow-up studies suggest a wider benefit in patients with other rhythms at presentation, patients with cardiogenic shock, and those requiring percutaneous cardiac intervention (i.e., angioplasty and stenting).2,3,10-18
Preliminary studies of therapeutic hypothermia for other indications including anaphylaxis, acute respiratory distress syndrome, heatstroke, myocardial infarction, near-drowning, near-hanging, pregnancy, strokes, status epilepticus, subarachnoid hemorrhages, toxins, and traumatic brain injury have reported only limited data or conflicting results.19-32 Recent studies have shown that therapeutic hypothermia in comatose pediatric patients who initially survived out-of-hospital arrest does not improve survival or neurologic outcome after 1 year.33 The exception is studies of neonates with perinatal asphyxia that reported similar results to adult cardiac arrest with a number needed to treat of six for one favorable outcome.3 Extensive research since 2002 has been conducted to determine the effectiveness of therapeutic hypothermia for other indications as well as the optimal timing, duration, target temperature, and techniques.
The International Liaison Committee on Resuscitation Recommendations (ILCOR) and American Heart Association (AHA) Resuscitation Guidelines for 2015 state that targeted temperature management is recommended between 32°C and 36°C and is to be maintained for at least 24 hours.34 The exact temperature for induction and maintenance of hypothermia is unknown.35-40 ILCOR recommends against routine use of prehospital cooling with rapid infusion of large volumes of cold intravenous fluids immediately after return of ...