Therapeutic hypothermia: A potent therapy
While hypothermia has been used during cardiac bypass since the 1950s, its use in the post-cardiac arrest setting had been unsuccessful until recently
By Jon C. Rittenberger, MD
Cardiac arrest is the most common cause of death in North America, resulting in approximately 350,000 deaths per year. For in-patients successfully resuscitated from out-of-hospital cardiac arrest, care is frequently withdrawn because of severe neurologic injury.
Consequently, survival following cardiac arrest is low nationwide, ranging from 3 to 16 percent. One potent therapy to reduce neurologic injury following cardiac arrest is therapeutic hypothermia — decreasing the body's temperature from 98.6° to approximately 91°F.
While hypothermia has been used during cardiac bypass since the 1950s, its use in the post-cardiac arrest setting had been unsuccessful until recently. In 2002, two large clinical trials showed that therapeutic hypothermia improved the percentage of neurologically intact survivors by 16 to 23 percent.
These trials limited therapeutic hypothermia to patients who were not following commands after resuscitation from out-of-hospital cardiac arrest due to VF/VT.
They used cold saline, ice packs and cooling blankets to induce and maintain hypothermia for either 12 or 24 hours following cardiac arrest. Complications of hypothermia therapy include: increased risk of bleeding, cardiac arrhythmias, infection, and development of seizures.
While the initial trials of hypothermia limited therapy to patients in a limited age range, primary rhythm of arrest, or out-of-hospital location, most cardiac arrest centers now provide this therapy to all patients who remain unable to follow commands following resuscitation from cardiac arrest.
Hypothermia in the press
Hypothermia has received a great deal of press coverage and is considered central to any post-arrest care plan. However, recent studies suggest that a comprehensive care plan incorporating therapeutic hypothermia with blood pressure and ventilation guidelines, glucose management strategies, neurologic prognostication guidelines, and rehabilitation plans optimizes outcomes.
Implementation of these care plans require significant resources and a constant quality improvement plan. Hospitals that care for greater than 50 cardiac arrest patients per year have better outcomes. Data from the Resuscitation Outcomes Consortium, a ten-city North American resuscitation consortium dedicated to improving survival from cardiac arrest, has shown that most hospitals see 10 to 15 cardiac arrest patients per year.
Consequently, many hospitals may simply refer post-arrest patients to cardiac arrest centers that offer comprehensive care for this disease.
Prehospital providers play a key role in the resuscitation and initial post-arrest care of these patients. A focus on providing excellent CPR, early defibrillation and avoidance of hyperventilation is key to establishing return of spontaneous circulation. Once this is accomplished, some states (Arizona, Minnesota, and Pennsylvania) encourage providers to transport patients to cardiac arrest centers.
While this may divert patients beyond the closest hospital, recent data suggest that diverting these patients to cardiac arrest centers in both ground transport and aeromedical transport is feasible and safe.
More prehospital intervention
Another potential prehospital intervention is infusion of cold saline to start inducing hypothermia. Pennsylvania state ALS protocols empower paramedics to start rapid infusion of cold saline, placement of ice packs in the groin and axillae, and benzodiazepine administration to induce hypothermia while enroute to the hospital. Locally, we have seen patients that receive prehospital cooling efforts arrive at goal temperature approximately 2.5 hours earlier than those whose cooling begins in the hospital.
In fact, some agencies in Virginia have started infusing cold saline during CPR, potentially resulting in hypothermia when return of spontaneous circulation is achieved. However, all of these agencies have established care plans to transport these patients to facilities that will continue hypothermia therapy after hospital arrival.
Improving outcomes from cardiac arrest requires a comprehensive care plan starting with EMS, and continuing aggressive care in the ED, ICU and rehabilitation unit. With the advent of hypothermia and titrated neurocritical care interventions, neurologically intact survival is improving from this common disease.