Medical therapy. Caution is advised because the reduced metabolism of a hypothermic patient can lead to potentially toxic accumulation of drugs peripherally. In fact, outcomes have not been positively influenced by routine use of medications, other than treatment of ventricular fibrillation with amiodarone.11 Any intravenous (IV) drug should be held until the patient’s core temperature is >30°C (>86°F).11
Vasopressors can be beneficial during rewarming for a patient in cardiac arrest and are a reasonable consideration.2 Nitroglycerin, in conjunction with active external rewarming, can increase the overall hourly temperature gain in a moderately hypothermic patient.13
Rewarming. The extent of rewarming required can be predicted by the severity of hypothermia (FIGURE3,11,12). Mildly hypothermic patients can generally be rewarmed using passive external measures. Patients with moderate hypothermia benefit from active rewarming in addition to passive measures. Intervention for severe hypothermia requires external rewarming and internal warming, with admission to the intensive care unit.
Treatment plans for severely hypothermic patients differ, depending on whether the person has a perfusing or nonperfusing cardiac rhythm. Patients who maintain a perfusing rhythm can be rewarmed using external methods (although core rewarming is used more often). Patients who do not have a perfusing rhythm require more invasive procedures.11 When using any rewarming method, afterdrop phenomenon can occur: ie, vasodilation, brought on by rewarming, causes a drop in core body temperature, as cooler peripheral blood returns to the central circulation. This effect may be reduced by focused rewarming of the trunk prior to rewarming the extremities.3
Rewarming for mild hypothermia patients begins with passive external techniques. First, the patient is moved away from the environment for protection from further exposure. Next, wet or damaged clothing is removed, blankets or foil insulators are applied, and room temperature is maintained at ≥28°C (82°F).3,11,13,14
If the patient’s temperature does not normalize, or if the patient presented with moderate or severe hypothermia, rewarming is continued with active external and internal measures. Active external rewarming can supplement passive measures using radiant heat from warmed blankets, air rewarming devices, and heating pads.3,13,14 Active internal rewarming techniques rely on invasive measures to raise the core temperature. Heated crystalloid IV fluids do not treat hypothermia, but do help reduce further heat loss and can be helpful in patients in need of volume resuscitation.3,13
Severely hypothermic patients might require more invasive active internal rewarming techniques, such as body-cavity lavage and extracorporeal methods. Body-cavity lavage can be facilitated with large volumes (10-120 L) of warm fluid at 40°C to 42°C, circulated through the thoracic or abdominal cavities to raise core body temperature 3°C to 6°C per hour.3,13
Extracorporeal rewarming can be achieved through hemodialysis, continuous arteriovenous rewarming (CAVR), continuous veno-venous rewarming (CVVR), or cardiopulmonary bypass.3,13 Research has shown cardiopulmonary bypass to be the most effective technique, with as high as a 7°C rise in core body temperature per hour; CVVR and CAVR are less invasive, however, and more readily available in hospitals.3,11,13
Rewarming interventions should continue until return of spontaneous circulation and core body temperature reaches 32°C (89.6°F) to 34°C (93.2°F).11 Overall, resuscitation efforts may take longer than normal due to the need for rewarming and should continue until the patient has achieved a normal temperature of 37°C (97.8°F).