Endovascular Catheter as a Rewarming Method for Accidental Hypothermia

Introduction

Accidental hypothermia can be a catastrophic condition. Prompt recognition, triage, and management are therefore required to circumvent potentially fatal outcomes. In spite of the relatively poor outcome, there are still no clear-cut guidelines in place for the treatment of accidental hypothermia. In general, the treatment approach depends on the degree of hypothermia. This can range from passive rewarming with warming blankets to more invasive approaches such as extracorporeal warming circulation. The choice of treatment modality is also very much dependent on the available resources and expertise that a health center has at its disposal (Kempainen and Brunette, 2004). As such, a less complex but effective modality is profoundly needed. With the recent widespread use of therapeutic hypothermia for cardiac arrest patients, there has been an increase in the availability of devices that can be used to safely and quickly cool these patients. One modality used is the endovascular (Zoll Corporation) temperature exchange system. The potential use of an endovascular catheter for rewarming is explored in the following case. Although its efficacy and safety as a cooling modality has been reported (Hoedemaekers et al., 2007; Pichon et al., 2007), there are limited data about the use as a rewarming strategy.

Case Report

An 89-year-old man with a history of diabetes mellitus and congestive heart failure was admitted to the Coronary Intensive Care Unit after he was found lethargic and confused at home. On assessment, his core temperature was ∼28.8°C. History was lacking at this point, but reports indicated that he had been seen by relatives 3 days before the incident in usual health. Upon arrival to the Emergency Department, he had a Glasgow Coma Scale of 13, was hypotensive with a blood pressure of 90/40 mmHg, was bradycardic with a heart rate of 40 beats per minute, and had a respiratory rate of 16 breaths per minute. He was subsequently fluid resuscitated with warm normal saline, and dopamine was initiated for blood pressure and chronotropic support. An endovascular (Icy catheter, Zoll Corporation) heat exchange device was placed in the inferior vena cava via the femoral vein. The device was then connected to the Zoll Coolgard temperature management unit and programmed for rewarming at MAX per hour until 36.0°C was reached. Repeat physical examination revealed an elderly man who was poorly kempt, lethargic, and confused, having decreased breath sounds with a few bibasilar crackles and exhibiting grade 3 pitting edema in both lower extremities. The rest of the systems were unremarkable. The laboratory workup was significant for anemia with a hemoglobin of 8.3 g/dL, a white count of 5.0 g/dl with 84.7% granulocytes, positive cardiac enzymes, mildly elevated lipase of 234 U/L, elevated thyroid stimulating hormone of 4.66, cortisol of 25.7 U/L, elevated alkaline phosphatase of 208 U/L, and negative blood and urine cultures. The electrocardiogram demonstrated an idioventricular rhythm with a rate of 33; his chest radiograph revealed congestive heart changes with a possible pneumonic infiltrate. A head computed tomography was completed and did not reveal any acute processes. He was started on a wide-spectrum antibiotic to cover the possibility of sepsis, transfused with packed red blood cells, and continued on dopamine drip while rewarmed. The target temperature of 36°C was achieved ∼8 hours after admission corresponding to about 1°C per hour. The patient's bradycardia resolved upon reaching ∼35°C and a repeat ECG on the second hospital day demonstrated a sinus rhythm at 72 beats per minute. He was weaned off of dopamine support on day 3 and was transferred out of the Coronary Intensive Care Unit on the 3rd hospital day hemodynamically stable.

Discussion

Accidental hypothermia remains a challenging clinical problem that carries important morbidity and therefore requires rapid recognition and treatment Brát et al. (2004). Over the past two decades, there have been ∼16,500 deaths stemming directly from accidental hypothermia in the United States; this translates to ∼689 deaths per year (CDC, 2005)

Accidental hypothermia is described as an unintentional fall in the core body temperature to <35°C and is classified as either mild (33°C–35°C or 90°F–95°F), moderate (28°C–32°C or 82°F–90°F), or severe (<28°C or <82°F) (Mallet, 2002; Aslam et al., 2006). It can cause significant disturbance in different organ systems of the body. The clinical manifestations depend largely on the degree of hypothermia.

Normal thermoregulation involves a tightly regulated balance between heat production and regulation of heat loss. This mechanism preserves the core temperature in a narrow physiologic range. It is achieved through a central thermogenesis and maintenance of a temperature gradient between the core and the peripheries in contact with the environment (Mallet, 2002).

Elderly people, as with the patient in this case, are particularly prone to accidental hypothermia because of a common age-related decline in the thermoregulatory (Mallet, 2002). Normal thermogenesis may be hindered by reduction in lean body mass, inadequate diet, and decrease in the shivering response.

Although the usual focus would be the deleterious effects of varying degrees of hypothermia; the rewarming period can potentially be dangerous as well. The concept of afterdrop has previously been reported (Kempainen and Brunette, 2004; Ban et al., 2008; Lasater, 2008). It usually occurs with external rewarming and is thought to be secondary to rewarming and vasodilation of the extremities in a severely hypothermic patient, wherein the cooler blood from the periphery is inappropriately shunted to the core and paradoxically drops the temperature. Rewarming of the trunk should therefore be initiated before the extremities to reduce this risk. Warming can also result in the precipitous drop in blood pressure that can occur with peripheral vasodilation during rewarming and from the negative ionotrophic effect of acidic blood from the cold extremities. Fortunately, this was not observed during the rewarming period of the patient in this case, likely due to the use of a central intravascular heat exchange system, in addition to adequate volume resuscitation that was done before initiating the rewarming process.

As mentioned previously, there are currently no strict recommendations regarding rewarming modalities for accidental hypothermia. In addition, there are no head-to-head studies evaluating one method of rewarming over another (Aslam et al., 2006). Nevertheless, literature would tend to favor a controlled rather than a drastic rewarming technique (Aslam et al., 2006; Lasater, 2008; Thompson and Kirkness, 2010) unless it is in the context of profound hypothermia, wherein rapid rewarming is advocated during the initial part of therapy (Laniewicz and Lyn-Kew, 2008). The choice of the rewarming method therefore depends on the degree of hypothermia and the healthcare expertise and resource. Passive external warming is often sufficient in patients presenting with mild hypothermia. Prompt removal of the patient from cold exposure and insulation from further heat loss are often the only interventions required with an intact shivering mechanism. Therefore, elderly patients, cachectic patients, or patients with severe cardiovascular disease may not be able to tolerate this and may need more aggressive rewarming methods. Moderate hypothermia usually includes loss of the shivering mechanism and will likely require external active rewarming, including forced air rewarming, warming blankets, and warm water immersion. Possible limitations to these methods include the possibility of an afterdrop effect as well as induction of hypotension. As mentioned, the vasodilation and return of cold blood from the periphery to the central circulation would account for these deleterious effects. While the methods described are usually effective for mild to moderate hypothermia, severe hypothermia will require a more urgent and aggressive measure. Invasive procedures such as active internal rewarming and extracorporeal methods require technical expertise and resources that may not be available in every healthcare organization. A review of available literature revealed that the most common of these methods are warmed intravenous fluids, body cavity lavage, hemodialysis, continuous ateriovenous rewarming, and cardiopulmonary bypass. Each method has its own limitations, advantages, and disadvantages. Here lies the need for newer methods that are more widely and readily available.

Endovascular heat exchange catheters are relatively new devices that have typically been used for the induction of mild therapeutic hypothermia in patients who have suffered cardiac arrest to prevent hypoxic or anoxic neurologic injury. Different studies to date have verified its efficacy in inducing hypothermia and maintaining a goal temperature with minimal fluctuations. Currently, there have been anecdotal reports of its use in rewarming (Ban et al., 2008; Cocchi et al., 2012; Laniewicz and Lyn-Kew, 2008; Lasater, 2008). An intravascular device has potential advantages compared to other traditionally invasive methods in that it can be started earlier than extracorporeal rewarming; it does not need arterial access; it is not dependent on blood pressure for circulation; and there are rare instances of overheating. In addition, its use results in a more stable and controlled temperature regulation (Hoedemaekers et al., 2007; Pichon et al., 2007; Taylor et al., 2008). At our institution, the Icy catheter is the primary method of hypothermia induction in patients who have had cardiopulmonary arrest. With less invasiveness and complications, it would seem to be a favorable tool for rewarming patients in a controlled manner. Further studies are needed to compare its use to other methods.