Will Prehospital Cooling Boost Survival?

September 2009

Hypothermia Initiation Studied

By Bruce Jancin
Elsevier Global Medical News

NEW ORLEANS -- Prehospital initiation of therapeutic cooling in comatose patients resuscitated from out-of-hospital cardiac arrest speeds time to goal temperature--but whether it improves clinical outcomes will require further study.

That was the key finding in a comparative study showing a trend, albeit not a statistically significant one, for enhanced survival of prehospital-cooled patients, compared with those with in-hospital initiation of therapeutic hypothermia, Dr. Jon C. Rittenberger reported at the annual meeting of the Society for Academic Emergency Medicine.

The observed difference in survival is a "provocative" finding that's going to require larger numbers of patients before definitive conclusions can be drawn regarding the benefits of emergency medical service-initiated prehospital cooling, stressed Dr. Rittenberger of the emergency medicine department at the University of Pittsburgh.

He is also a member of the Pittsburgh medical center's novel post-cardiac arrest service. Its mission was initially to ensure that all post-cardiac arrest patients are at least considered for therapeutic hypothermia. As part of a quality improvement initiative, however, the service's mission has expanded to include responsibility for care of patients with out-of-hospital cardiac arrest from the prehospital stage through rehabilitation.

It is now well established that inducing mild hypothermia to a temperature of 32-34° C improves neurologic outcomes in patients resuscitated from cardiac arrest. A recent European study demonstrated that a shorter time to attainment of 33° C was associated with better outcomes, much like early thrombolysis in the setting of acute MI.

The problem Dr. Rittenberger and colleagues regularly encounter is that roughly half of the patients on their post-cardiac arrest service are referred from outlying institutions. So, the investigators sought to learn whether prehospital initiation of hypothermia by an EMS team is feasible, safe, and improves outcomes.

He presented a retrospective study of the hospital and EMS records of all patients who underwent therapeutic hypothermia after remaining comatose following resuscitation from out-of-hospital cardiac arrest during 2006-2008. Rather than using the Glasgow Coma Score, the Pittsburgh group for this purpose defines "comatose" as "not following commands."

Prehospital cooling using cold saline was initiated in 44 patients, in-hospital cooling in 68 patients. Time to the goal temperature of less than 34° C averaged 2.3 hours faster in the EMS-initiated group. The complication of overshoot to a temperature below 32° C occurred in 32% of patients with prehospital and 23% with hospital-initiated hypothermia. Fortunately, Dr. Rittenberger noted, the time spent in overshoot was fairly brief: an average of 1.4 hours in the EMS-cooled group and 0.9 hours in exclusively hospital-cooled patients.

The patient survival rate was 39% in the prehospital-cooled group, compared with 23% with hospital-initiated cooling. Again, that difference was not statistically significant. Neither was the trend for the prehospital-initiated cooling group to have a higher rate of good outcomes as defined by discharge home or to an acute rehabilitation facility.

Planned additional studies will attempt to pin down the optimal time to achieve goal temperature, as well as its most beneficial duration. The cooling protocol used by the investigators is available at www.emsresearch.org.

Dr. Rittenberger's study was supported by several nonprofit research foundations.


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