Literature Review: Hypothermia During ALS
The authors assessed the feasibility, safety and effectiveness of therapeutic infusion of two liters of 4ºC normal saline before the return of spontaneous circulation during CPR after out-of-hospital cardiac arrest.
Bruel C, Parienti JJ, Marie W, et al. Mild hypothermia during advanced life support: A preliminary study in out-of-hospital cardiac arrest. Crit Care 12(1), Feb 29, 2008.
Abstract
The authors assessed the feasibility, safety and effectiveness of therapeutic infusion of two liters of 4ºC normal saline before the return of spontaneous circulation during cardiopulmonary resuscitation after out-of-hospital cardiac arrest (OHCA).
Methods
This was a prospective, observational multicenter clinical trial conducted in emergency medical services units and in a medical intensive care unit.
Results
Hypothermia was induced by infusing two liters of 4ºC NaCl 0.9% into OHCA subjects over 30 minutes during advanced life support. Thirty-three subjects were included in the study. Eight patients presented with ventricular fibrillation as the initial cardiac rhythm. Mild hypothermia was obtained after a median of 16 minutes (interquartile range 11.5--25) following the return of spontaneous circulation. After intravenous cooling, the temperature decreased by 2.1ºC (p
Conclusions--The authors concluded that prehospital induction of therapeutic hypothermia using infusion of two liters of 4ºC normal saline during ALS was feasible, effective and safe. Larger studies are required to assess the impact of this early cooling on neurological outcomes after cardiac arrest.
Comment
Therapeutic hypothermia after cardiac arrest was first described in the late 1950s. After being shown to improve outcomes following brain surgery, it was used on a limited number of cardiac arrest patients. No true studies were done, though, and it was soon abandoned. In the 1990s interest was revived when animal and human studies showed benefit.
In 2002 two studies concluded that patients who were resuscitated from ventricular fibrillation and treated with hypothermia for 12--24 hours had better neurological outcomes (brain function) than control patients treated with standard care. Based on these and other studies, the 2005 American Heart Association CPR/ECC guidelines listed therapeutic hypothermia as a Class IIa recommendation (i.e., the weight of evidence supports it, and it's reasonable to perform) for unconscious patients resuscitated from ventricular fibrillation and a Class IIb (unclear evidence, may be considered) for other rhythms.
More important for EMS is that it appears that the earlier the patient is cooled, the better the response. Delays of as little as 15 minutes worsen outcomes in animal studies.
It is not known how hypothermia improves brain healing. We do know that it reduces metabolic demand, oxygen free radicals and other inflammatory responses, which results in less cerebral edema and lower intracranial pressures. However, which of these (if any) is most important in improving brain recovery is still not known.
More research is needed to determine which patients will best benefit, how to cool them (IV fluids, external cooling or other), when, to what degree and for what duration. For now, though, it is reasonable for EMS systems to begin to evaluate whether this makes sense to introduce.
Angelo Salvucci, Jr., MD, FACEP, is an emergency physician and medical director for the Santa Barbara County and Ventura County (CA) EMS Agencies.
Related:
- Sept. 2008 Cover Report: Raising the Dead
