Rapid Rewarming of Hypothermic Patient Using Arctic Sun Device

Introduction

With the recent widespread use of induced mild hypothermia to improve neurologic recovery and survival in patients after successful resuscitation from cardiac arrest, several devices have become available to facilitate the rapid and safe cooling of these patients to goal temperature typically between 32°C and 34°C. We describe a case in which a patient suffering from severe accidental hypothermia secondary to environmental exposure was rapidly warmed using a commercially available temperature management device (Arctic Sun) traditionally used for therapeutic hypothermia (TH) in patients with post-cardiac arrest. While the use of the Arctic Sun for rewarming rather than cooling patients has been described previously,^1,2 this strategy had not been previously employed at our hospital and is infrequently described in the medical literature.

Case Report

A 55-year-old male was transferred to our emergency department (ED) by aeromedical transport from a community hospital ED after being found unresponsive on the local train tracks. The patient was transported initially to the first hospital, where intubation and mechanical ventilation was immediately established. The patient was noted at that time to have a core temperature (measured by rectal thermometer) of 23°C. Warming techniques using heated intravenous normal saline, an external warming blanket, and bladder irrigation with warmed saline were initiated at the first hospital and continued during air transport. On arrival in our ED, the patient was hemodynamically stable, with a heart rate in the 40 to 50 beats per minute range and a blood pressure of 103/74 mm Hg. The core temperature on arrival was 27°C measured continuously by rectal thermometer. An initial electrocardiogram (ECG) revealed slow atrial fibrillation. On examination, the patient was noted to have fixed and dilated pupils, did not withdraw to pain, and had evidence of frostbite on the upper and lower distal extremities. He had received no sedation at any time during his care prior to arrival in our ED. A toxicology screen was positive for cocaine and opiates. The lactate level on admission was 8.0 mmol/dL.

In the trauma bay, care was taken to avoid excessive movement of the patient given the concern for inducing a more serious arrhythmia in the setting of myocardial irritability due to severe hypothermia. The patient underwent computed tomography of the head, cervical spine, and torso, which did not reveal any evidence of traumatic injury. The patient was placed on a heated ventilation circuit, in which the inspired oxygen is warmed to 37.0°C. The patient was transferred to the trauma intensive care unit (TICU). On arrival in the TICU, the external thermoregulation device used at our hospital for induced therapeutic hypothermia in survivors of cardiac arrest (Arctic Sun) was applied to the patient, and a goal temperature was set at 37°C. A femoral central venous catheter and a radial arterial catheter were placed. Of note, we chose the femoral position for the central line to avoid the risk of inducing a ventricular dysrhythmia with the guidewire during insertion of a central venous catheter in the subclavian or internal jugular positions.

Using the Arctic Sun device, the patient was rapidly warmed, achieving a core rectal temperature of 31.4°C within 1 hour, and reaching a goal temperature of 37°C in 4 hours; aside from the heated ventilation circuit, no other rewarming modalities or interventions were employed. During this time, the patient converted to normal sinus rhythm. A repeat lactate level was 1.4 mmol/dL. The patient was extubated the following day and made a complete neurologic recovery. The frostbite improved and did not require surgical intervention.

Discussion

We report this case of a patient with severe accidental environmental hypothermia who was rapidly and effectively rewarmed using the Arctic Sun, a device that is generally used for inducing hypothermia in patients with postcardiac arrest.

Environmental exposure can lead to significant hypothermia, which if untreated can be fatal. ³ Generally, the stages of hypothermia are defined as mild, moderate, and severe, and the choice of warming methods will often depend on the degree of severity of the hypothermia. For example, for mild hypothermia, methods such as warming blankets may be sufficient. In severe cases, particularly when hemodynamic instability is present, more aggressive methods may be required, which traditionally have centered on invasive modalities such as thoracic cavity lavage ⁴ , intraperitoneal lavage with warmed saline, ⁵ or warming of the blood via a hemodialysis circuit or extracorporeal membrane oxygenation (ECMO). ⁶

The rewarming period can be potentially dangerous as well, as hypotension from vasodilatation can occur and may require fluid resuscitation and augmentation of vascular tone with the use of vasopressors. The concept of “core afterdrop” has been cited as a concern as well, where the core body temperature drops during the rewarming phase, likely secondary to redistribution of body heat to colder peripheral areas. ⁷ Another potential complication commonly seen during the rewarming of patients with accidental hypothermia is cardiac arrhythmia, including supraventricular tachycardias, ventricular ectopy, and asystole. Generally, benign dysrhythmias such as slow atrial fibrillation do not require specific treatment beyond treating the underlying cause (hypothermia). ⁸ Given the myocardial irritability caused by changes in cardiac repolarization related to severe hypothermia, it is generally held that excessive movements or interventions which could potentially cause further myocardial irritability should be avoided, although there is sparse evidence in the medical literature to support this axiom.^9,10 In our patient, we did not observe the afterdrop phenomenon, and although he initially presented in slow atrial fibrillation, he quickly converted to sinus rhythm during warming and never developed any other dysrhythmias.

In our hospital, the Arctic Sun device is used to induce and maintain therapeutic hypothermia in patients with postcardiac arrest for a period of 24 hours, and then rewarm these patients slowly over a period of 12 to 16 hours. Special pads containing a thin layer of hydrogel are placed over large surface areas of the body and temperature-adjusted water is circulated through those pads to allow thermal transfer. While used primarily in the postarrest circumstance, there are data to support the effectiveness of this device in noncardiac arrest scenarios. In a study that evaluated the use of the Arctic Sun device in preventing hypothermia in patients undergoing off-pump coronary artery bypass graft (CABG) surgery, the authors found that patients who were placed on the Arctic Sun were protected from hypothermia much better than those who underwent traditional hypothermia prevention techniques (increased ambient room temperature, heated intravenous fluid, and a forced air warming system). ¹ In a case of near drowning, a patient suffering from environmental hypothermia was successfully warmed from 32.7°C to 36.5°C over 6 hours using the Arctic Sun device. ²

Given that our patient, despite being severely hypothermic, was hemodynamically stable, the decision was made to try minimally invasive methods of warming before resorting to more invasive methods such as thoracic cavity lavage via bilateral chest tube thoracostomy, which carries the risks of cardiac irritation and infection. Furthermore, the intensivist (MNC) caring for this patient had extensive experience using the Arctic Sun device for induced hypothermia in patients with postcardiac arrest and was able to directly facilitate the application of the device and monitor the patient at the bedside. Using this noninvasive device, our patient was rapidly and safely warmed, without any complications, and was successfully extubated several hours after achieving normothermia, without any neurologic sequelae.

The rate of rewarming in our patient was more rapid than generally used for rewarming in the setting of induced therapeutic hypothermia for neuroprotection after cardiopulmonary arrest, which is generally approximately 0.5°C per hour.^11,12 However, rewarming in the setting of environmental hypothermia generally happens at a faster rate; indeed, rates of rewarming of 7°C to 10°C per hour have been achieved safely using cardiopulmonary bypass in the setting of circulatory collapse related to profound hypothermia. Most studies in the literature describe mean rewarming times of 1°C to 2°C per hour, depending on technique utilized.^13–15

Conclusion

This case report highlights the use of a commercially available thermoregulation device that while traditionally used for the purpose of cooling patients functioned quite effectively in the opposite role to rapidly warm a patient suffering from accidental environmental hypothermia. Providers in the ED or intensive care unit may consider the use of this and other similar devices when faced with this type of clinical scenario.