Characteristics of Long- Term Survivors of Profound Accidental Hypothermia

ABSTRACT & COMMENTARY

Source: Walpoth BH, et al. Outcome of survivors of accidental deep hypothermia and circulatory arrest treated with extracorporeal blood warming. N Engl J Med 1997;337: 1500-1505.

The authors from several institutions in Switzerland reviewed the medical records of 234 patients with environmental, accidental hypothermia complicated by circulatory arrest. Of these 234 cases, 46 patients were labeled as deep hypothermia with a core body temperature of less than 28°C. Rewarming was attempted in 32 patients via the extracorporeal technique, resulting in 15 long-term survivors who were used for data analysis.

The mean age of the study group was 25 years (range, 9-43 years) with 53% being male. The mechanisms of deep hypothermia included boating mishaps, mountaineering accidents, suicide attempts, and criminal violence. All patients were unresponsive at discovery and received aggressive cardiopulmonary resuscitation including endotracheal intubation soon after the loss of vital signs. On admission to the ED, 10 patients demonstrated ventricular fibrillation, and five demonstrated asystole; all had fixed and dilated pupils. Extracorporeal blood rewarming was initiated a mean of 141 minutes after discovery. The extracorporeal technique consisted of standard cardiopulmonary bypass rewarming by a cardiovascular surgeon. Upon discharge from the hospital, the following medical issues were still active: pulmonary (11 patients), neuropsychiatric (10 patients), neurologic (9 patients), renal (5 patients), and cardiac (4 patients). Five patients were discharged home, while the remaining 10 cases were transferred to other medical facilities.

After a mean time interval after the hypothermic episode of 6.7 years, all survivors were contacted and examined with standard history and physical examinations as well as neurologic and neuropsychiatric testing, neurovascular studies, electroencephalography, and magnetic resonance imaging of the brain. At follow-up, there were no hypothermia-related deficits encountered that impaired quality of life. The neurologic and neuropsychiatric problems had either fully or almost completely resolved. One patient demonstrated cerebellar atrophy on MRI with mild clinical signs that may have been related to the hypothermia. Other ongoing clinical issues were either pre-existing or not related to the actual hypothermia.

COMMENT BY WILLIAM BRADY, MD

This impressive survival rate may be explained in one of several ways, including profound hypothermia with its cerebroprotective effects, the absence of hypoxic brain injury prior to cardiopulmonary bypass rewarming, overall young patient age without significant comorbidity, rapid evacuation from the scene with prompt application of aggressive supportive care, and the extracorporeal technique itself. Such a technique is, of course, limited to larger medical centers with such invasive capability. Nonetheless, in victims of accidental, environmental, profound hypothermia, long-term survival with good neurologic status is encountered in approximately one-half of those patients treated with extracorporeal rewarming despite coma with fixed, dilated pupils and the absence of spontaneous circulation. The emergency physician, either in a large medical center or with rapid transfer access to such institutions, must recognize potential candidates for rewarming therapy. Such transfers must be initiated as soon as possible with the simultaneous use of aggressive cardiopulmonary resuscitation.

Initial clinical characteristics of patients with ultimately positive outcomes after hypothermia complicated by cardiopulmonary arrest who are rewarmed via the extracorporeal technique include all of the following except:

a. young age.

b. temperature less than 28°C.

c. cardiac rhythms other than asystole on initial examination.

d. absence of significant comorbidity or prior, event-related hypoxic brain injury.

e. environmental exposure-related hypothermic etiology.