Temperature should be closely monitored to keep the patient in the 32° C to 34° C (89.6° F to 93.2° F) range.² The patient should be paralyzed and sedated to prevent shivering, which increases the metabolic rate and oxygen demand and may increase the incidence of myocardial infarction.²¹ However, reduction of core temperature by 1°C typically takes about 30 minutes using cold saline and does not trigger a thermoregulatory response, allowing paralytics to be delayed until the patient’s arrival in the emergency department, even if cooling is begun in the ambulance.¹⁹ As these are comatose patients who are going to be pharmacologically paralyzed, a secure airway should be in place prior to inducing hypothermia. Cooling should be continued for 12 to 24 hours, after which patients should be rewarmed slowly (0.25°C to 0.5°C per hour), and subsequent hyperthermia should be avoided.^2,7,22

CRITICAL DECISION
What are the complications of therapeutic hypothermia?
In the ERC HACA study, 3% of patients suffered hemorrhage and 6% suffered arrhythmia, but overall there were no deaths attributed to therapeutic hypothermia, and there was no significant difference in complication rates between patients cooled by the endovascular method and those cooled by other methods.33 The initial randomized controlled trial by Bernard found no clinically significant cardiac arrhythmias but did find clinically unimportant hyperkalemia.⁵ They also noted an increase in hyperglycemia in the hypothermia group.5 It is reasonable to monitor for cardiac arrhythmia, hemorrhage, hyperglycemia, hyperkalemia, and infection.^2,7

CRITICAL DECISION

Can a patient undergoing therapeutic hypothermia receive cardiac catheterization?

A feasibility study of 40 patients who underwent PCI and therapeutic hypothermia compared to historic controls with PCI only found no difference in peak lactate, need for vasopressors or inotropes, aortic balloon pump use, repeat cardioversion/defibrillation, renal function, oxygen requirements during mechanical ventilation, or use of antiarrhythmics, while demonstrating a 39% increase in neurologically intact survival.⁸ A 2012 study published in Resuscitation reported similar findings.³⁴ It is therefore reasonable to start cooling prior to PCI and to continue it throughout the procedure as long as the cooling method does not interfere with performance of the procedure.

Case Resolution

En route to the hospital with the man who had arrested at work, paramedics started therapeutic hypothermia using icepacks in the patient’s axillae and groin and administering a 30-mL/kg bolus of normal saline cooled to 4° C (39.2° F). Ventilation was provided by bag-valve-mask, carefully avoiding hyperventilation. On arrival at the emergency department, the patient’s vital signs were blood pressure 110/70, heart rate 80, and temperature 95.9° F (35.5° C). An esophageal temperature probe was placed, ice packs were changed, and the patient was placed on a cooling blanket before being transported to the cardiac catheterization laboratory. Following balloon angioplasty and stenting, the patient went to the ICU, where hypothermia was continued for 24 hours. He was then slowly rewarmed at 0.25° C (0.5° F) per hour while being weaned off the sedation, paralytics, and ventilator. Finally, after 10 days and placement of an internal defibrillator, he was discharged home with a full neurologic recovery.

Summary

Historically, rates of survival with full neurologic recovery after cardiac arrest have been dismal. Therapeutic hypothermia appears to increase a patient’s chance of survival with a good neurologic outcome. Patients with a witnessed ventricular fibrillation arrest, bystander CPR, and return of spontaneous circulation prior to transport to the emergency department already have the best chance of survival, and therapeutic hypothermia further improves their chances for a good neurologic recovery. Other rhythms may benefit too. Despite the evidence and AHA guidelines, institutions have been slow to adopt therapeutic hypothermia policies. Studies showed that only 23% to 26% of US physician members of the Society for Academic Emergency Medicine, the AHA, and the American Thoracic Society and only 16% of US emergency physicians use therapeutic hypothermia.^35,36 Therapeutic hypothermia has the potential to save lives, and we advocate more widespread use.

Questionnaire Available Online

This educational activity is designed for emergency physicians and should take approximately 1 hour to complete. Participants will need an Internet connection through Firefox, Safari, or Internet Explorer 6.0 or above to complete this Web-based activity. The CME test and the evaluation form are located online at www.ACEP.org/focuson.