Hypothermia Complications and Associated Electrocardiogram (EKG) Findings

Abstract

Hypothermia is a relatively common occurrence typically seen in the emergency department (ED) during the winter months. The condition is defined by a decrease in core body temperature and classified by severity, based on temperature ranges from mild to severe. While initial symptoms have correlated with core body temperature, patient outcomes have not demonstrated a correlation. Shock occurs secondary to bradycardia and increased cardiac excitability, leading to arrhythmia, and hypotension can occur during rewarming if the peripheral vasculature is warmed prior to the core body. In this case, a woman was found unconscious in the early morning after spending the night outside without appropriate clothing. She was brought to the ED, and upon arrival, her rectal temperature was confirmed to be 28.3°C, placing her in the moderately hypothermic category. This case is an example of not only the initial symptoms of moderate hypothermia but also possible complications during rewarming, making it very important in the field of Emergency Medicine.

Introduction

Hypothermia is the condition of decreased core body temperature. Accidental hypothermia from exposure is possible in any climate or time of year, but firm values for the incidence of cases are not thoroughly published. It is imperative that the patient is assessed quickly and that an accurate core body temperature is obtained, and the initial evaluation must include an electrocardiogram (EKG) to identify any clinically relevant arrhythmia. Appropriate rewarming techniques decrease the risks and further complications that can be associated with hypothermia. This specific case shows EKG changes specific to hypothermia as well as potential hypotension that can occur during rewarming [1].

As defined by Zafren [1], hypothermia is a multifactorial condition that takes ambient temperature, age, sex, past medical history, and region into account. Typically, healthy patients who develop accidental hypothermia and are stable from a hemodynamic perspective will survive and have no loss of neurological function [1]. Hypothermia is known to have generally positive outcomes, with mortality not directly linked to core temperature, but instead to the development of a life-threatening arrhythmia or bradycardia [1,2]. Pirnes et al. provide a retrospective study from Finland that asserts that the two factors most associated with 30-day mortality were alcohol abuse and patient age over 65 years [3].

Mild hypothermia is defined as a core temperature of 32-35°C. Moderate hypothermia is considered for core temperatures of 28-32°C. Severe hypothermia is diagnosed once core temperatures fall below 28°C. Symptoms increase in severity based on classification, ranging from shivering in mild hypothermia to coma and death in severe hypothermia [1].

The most important step to take in the care of the hypothermic patient is rewarming. Immediate care starts with removing the patient from the cold environment and wet clothing. Rewarming is divided into different categories, including passive external, active external, and active internal core rewarming. The specific method of rewarming is based on which classification of hypothermia is identified [1].

Mild hypothermia is treated with passive external rewarming, which includes covering the patient in blankets (or other insulation) and maintaining the room temperature at approximately 28°C if possible. This helps prevent heat loss to the air as well as preserve the patient’s intrinsic heat production. Passive external rewarming may not be sufficient if further underlying abnormalities are present, such as hypoglycemia, sepsis, and hypovolemia, and this is especially true in older adult populations, as they do not have normal metabolic and cardiovascular homeostasis abilities and will likely require components of active rewarming [1]. The goal of passive external rewarming is to raise the core body temperature between 0.5 and 2°C/hour [2].

Active external rewarming includes a combination of warm blankets, heating pads, radiant heat, warm baths, or forced warm air applied directly to the patient’s skin, with the goal of increasing temperature by at least 2°C/hour. This category of rewarming is used for moderate to severe hypothermia. Rewarming the patient’s trunk prior to the extremities can minimize the hypotension and acidemia associated with peripheral arterial vasodilation. These shifts during rewarming are thought to contribute to fatal dysrhythmias that occur during the rewarming process [1].

Patients with core temperatures of <28°C or those with moderate hypothermia not responding to prior rewarming measures should be started on active internal rewarming. These methods include endovascular temperature control catheters, irrigation of the peritoneum or thorax with warmed isotonic crystalloid, or, if available, extracorporeal life support (ECLS). The goal is an increase in temperature by 2-3°C/hour. Other active internal rewarming options include venous rewarming (increases by 3-4°C/hour), cardiopulmonary bypass (increases by up to 9.5°C/hour), and extracorporeal membrane oxygenation (ECMO). Slower rewarming with ECLS has been associated with improved survival and neurological outcomes per the 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care: Hypothermia Circulation [1,4].

Zafren, in Frostbite: Acute Care and Prevention, also discusses frostbite treatment [5]. Rewarming of frostbitten regions is most effective by immersing the area in water heated to 37-39°C [5]. This can be very painful for the patient, and appropriate analgesia should be provided. If there are no contraindications and presentation is within 24 hours of injury, intravenous (IV) or intra-arterial tissue plasminogen activator (tPA) plus subcutaneous low-molecular-weight heparin/IV heparin have been used [5]. This is because of the associated vascular thrombosis in frostbitten areas. Wound care will be required after the rewarming process, but prophylactic antibiotics are considered controversial at this time. If there is any evidence of infection, then parenteral antibiotics to cover staphylococci, streptococci, and pseudomonas species should be started [5]. Topical antibiotics should be avoided, as these could lead to tissue maceration. Early surgical consultation is also recommended [5].

Cold temperatures are a cardiac irritant that acts to increase the chance of ventricular arrhythmias in the event of rough handling [1]. This cardiac irritation should not prevent lifesaving interventions. The duration of resuscitation can greatly vary, especially when compared to baseline Advanced Cardiac Life Support (ACLS) guidelines [1]. Hypothermia has neuroprotective effects, which have been demonstrated in patients with hypothermia and cardiac arrest having complete neurological recovery despite prolonged resuscitation lasting possibly up to hours [1]. Resuscitation should not be terminated because of low end-tidal CO2 (<10 mmHg), as this may be more associated with the diminished metabolic rate rather than poor perfusion. Laboratory markers can also influence resuscitative efforts. Cell lysis occurs with hypothermia, leading to profound hyperkalemia. Survival with serum hyperkalemia of 12 mEq/L or more has not been reported. Some case reports have recommended lower cutoffs of 8 mEq/L to discontinue resuscitation as well. Other markers that influence resuscitation efforts include evidence of intravascular thrombosis, such as fibrinogen concentration <50 mg/dL, ammonia >420 mcg/dL, and elevated lactate, sodium, or creatinine, as these are indicative of poor prognosis [1].

Prutkin discusses Osborn waves and other EKG changes consistent with hypothermia [6]. Hypothermia leads to slow conduction of the impulse through cardiac tissue, resulting in prolongation of EKG intervals such as RR, PR, and QRS. The Osborn waves, seen as J-point elevation, are due to disturbances in membrane repolarization. Prutkin goes on to describe that the Osborn waves are most likely to be seen in precordial leads V2-V5 and are more pronounced with increased severity of hypothermia [6].

This case discusses the treatment of a 43-year-old woman with moderate hypothermia and altered mental status. The patient was found unconscious outside in the morning by police responding to a missing person report. She was found unconscious in soiled, wet clothes and was brought to the ED for evaluation. This case is a good example of the preferred method of treating hypothermia, the possible consequence of rewarming hypotension via peripheral vasodilation, and the classic EKG change of Osborn waves that can be observed in hypothermia.

Case presentation

The patient is a 43-year-old female presenting to the emergency department (ED) after being found unresponsive. The patient was last seen at 00 the day before. At approximately 00 the next day, the patient was found unresponsive next to train tracks, missing her right shoe and wearing wet clothing. The family denied a history of similar events in the past. Overnight temperatures were in the -1.1 to -4.4°C range, with an overnight low of 1.7°C according to weather records. Vital signs on initial presentation were noted to be a rectal temperature of 28.3°C, pulse 79 beats per minute (bpm), respiratory rate 17 breaths per minute, blood pressure (BP) 116/105 mmHg, and pulse oximetry 95% on room air. On physical exam, the patient was noted to be minimally responsive and aroused to verbal and physical stimuli. The patient was cold to the touch and had damp clothing. Her right foot appeared mottled, with cyanosis extending from the toes up to the ankle. The left foot was cold but not mottled, likely because her shoe was still in place.

She was removed from her cold, wet clothes, and warm blankets were applied over her. IV access was obtained, and a bolus of warmed Lactated Ringer’s (LR) IV fluids was initiated. A Bair Hugger rewarming device was utilized to attempt to raise her body temperature. Bair Hugger rewarming had to be discontinued because of developing hypotension, as the patient demonstrated decreasing BP, dropping to near 80/30 mmHg. BP improved with discontinuation of the Bair Hugger and continued use of warm blankets and warmed fluids. When applying warm blankets, the patient’s extremities were left exposed to avoid further peripheral vasodilation. Mentation improved while in the ED as well. The surgical team was consulted for evaluation because of concern over the skin findings on the right foot, possibly indicating frostbite, but the surgical service did not evaluate the patient in the ED.

Complete blood count (CBC) showed leukocytosis at 27.3 g/dL (Table 1), likely secondary to the stress of cold exposure, as leukocytosis is a nonspecific inflammatory response. Complete metabolic panel (CMP) was notable for elevated creatinine at 1.4, consistent with acute kidney injury (AKI) (Table 2). Creatine kinase (CK) was elevated at the time of admission at 2348 units/L, indicating acute rhabdomyolysis, especially given the associated AKI (Table 2). Both creatinine and CK were monitored throughout the hospital course following admission to the intensive care unit (ICU). Lactic acid was initially elevated at 12.1, which improved during her stay (Table 2). Lactic acid is produced by anaerobic metabolism and is likely related to the patient’s overall poor perfusion due to peripheral vasoconstriction and hypotension, as well as poor perfusion to her kidneys. Urinalysis was positive for blood and protein, which could be related to the elevated CK, elevated creatinine, and early rhabdomyolysis, but was not clinically relevant to resuscitation in the ED, as the patient was being resuscitated with fluids and was to be admitted to the ICU with follow-up labs planned (Table 3 and Table 4). Computed tomography (CT) imaging of the head and brain, cervical spine, chest, abdomen, and pelvis showed no acute findings. EKG on presentation showed normal sinus rhythm at 77 bpm, with Osborn waves found on leads I, aVL, and V2 (Figure 1). The patient was admitted to the ICU for further management.

The patient’s mentation recovered while in the ICU and, on the second day of admission, she was found to be alert and oriented to person, place, and time, with a core body temperature within the normal physiological range. The patient remained normotensive in the ICU following admission. Lactic acid decreased during the patient’s stay in the ICU and was not thought to be clinically relevant, given that it was improving and the patient’s clinical presentation had improved so dramatically following admission. CK was elevated at the time of admission at 2,348 units/L and increased to 8,178 units/L on the second day of her inpatient stay. This is consistent with rhabdomyolysis, which is likely due to prolonged downtime and peripheral vasoconstriction during hypothermia and hypotension. Given concern over the abnormal appearance of her right foot on initial presentation, the surgery service physicians were consulted to evaluate her in the ICU. They initially found cold lower extremities with diminished sensation that improved on the second day of admission. The surgeon advised against acute surgical intervention at the time of evaluation, with low suspicion for compartment syndrome to explain the elevated CK on chemistry. Sensation in the lower extremities improved as well during admission. Venous duplex ultrasound of the right lower extremity showed no sign of deep vein thrombosis (DVT) (Figure 2 and Figure 3). Her right lower extremity began to demonstrate edema, warmth, and tenderness to palpation, and the patient was started on cefazolin for possible cellulitis. CK trended to below 5,000 units/L, and the patient was transferred to a tertiary care center, where she stayed two additional days before being discharged home on cephalexin.

Discussion

Hypothermia is a significant health concern in the United States. For comparison, according to the CDC, in 2021, the age-adjusted death rate for hyperthermia was 0.4 per 100,000 people [7]. Hypothermia in 2022 was described as having an overall age-adjusted death rate of 0.92 per 100,000 [8]. This is especially concerning given that the hypothermia death rate in the United States has increased significantly when compared to 1999, when it was 0.44 per 100,000 [8].

Additionally, hypothermia can lead to a multitude of complications, including, but not limited to, electrolyte derangement and malignant arrhythmias, leading to death. Per a historical retrospective study, patient outcomes have not correlated with core temperature upon initial patient presentation [1]. Hypothermia is considered after the core body temperature, determined by rectal temperature, decreases to <35°C. Mild hypothermia is defined as a core temperature of 32-35°C, with patients often presenting with confusion, tachycardia, and increased shivering in an attempt to warm themselves [1]. Moderate hypothermia is considered for core temperatures of 28-32°C, with symptoms of lethargy, bradycardia or arrhythmia, decreased or absent pupillary reflexes, and decreased or absent shivering [2]. Severe hypothermia is diagnosed once core temperatures reach below 28°C, with patients presenting with coma, hypotension, arrhythmia, pulmonary edema, and rigidity [1]. The most important step to take in the care of the hypothermic patient is to start rewarming as quickly as possible [9]. Immediate care includes removing the patient from the cold environment and wet clothing.

Cold temperatures are a cardiac irritant, which increases the chance of ventricular arrhythmias [1,4]. This cardiac irritation should not prevent lifesaving interventions, but it is very important to consider. As stated, it is strongly advised to remove wet clothing immediately, but it is important to do so gently because of associated cardiac irritability. Patients with severe or even moderate hypothermia have increased cardiac irritability, and movement may cause fatal arrhythmia. As described by Paal et al., witnessed cardiac arrest at the time of extrication or transfer is called rescue collapse [9].

Duration of resuscitation can greatly vary, especially when compared to baseline Advanced Cardiac Life Support (ACLS) guidelines [1]. Hypothermia has neuroprotective effects, which have been demonstrated in patients with hypothermia and cardiac arrest having complete neurological recovery despite prolonged resuscitation lasting possibly up to hours [1]. Resuscitation should not be terminated in the presence of low end-tidal CO2 (<10 mmHg), as this can be associated with the diminished metabolic rate rather than poor perfusion. Laboratory markers can also influence resuscitative efforts. Cell lysis occurs with hypothermia, leading to profound hyperkalemia. Survival with serum hyperkalemia of 12 mEq/L or more has not been reported. Some case reports have recommended lower cutoffs of 8 mEq/L to discontinue resuscitation. Other markers that influence resuscitation efforts include evidence of intravascular thrombosis, such as fibrinogen concentration <50 mg/dL, ammonia >420 mcg/dL, elevated lactate, sodium, or creatinine, as these are indicative of poor prognosis [1].

This patient was noted to be moderately hypothermic at 28.3°C upon arrival in the ED with lethargy. Li outlines the treatment of hypothermia and patient management in a 2021 article and states that shock due to peripheral vasodilation is a potential risk of surface rewarming [10]. The Merck Manual (Professional Version) also recommends only applying warmth to the thorax to avoid rewarming the extremities, instead describing an increased metabolic demand on an already strained cardiovascular system [11]. Our patient did indeed develop hypotension following the initiation of rewarming with a Bair Hugger, and it is important to note that the patient did have the warmer applied to her thorax and extremities. When her blood pressure was noted to decrease, the Bair Hugger was removed, warm blankets were applied to her torso, and she was given warmed IV fluids. Her blood pressure recovered, and the event serves as an example of a potentially fatal complication of rewarming a hypothermic patient.

On initial examination, the right foot demonstrated concern for frostbite; however, the appearance of the foot improved during hospitalization without surgical intervention. It was possible the patient had chilblains; however, skin changes reversed without direct specific intervention to the lower extremity. It is worth noting that the patient did begin to demonstrate findings consistent with cellulitis in the days following her inpatient admission to the ICU, and antibiotics were again initiated, with oral antibiotics continued after discharge for this purpose. Typically, prophylactic antibiotics are considered controversial in the treatment of frostbite. In this case, the initial findings were mild, and antibiotics were given in the ED, but only restarted when the patient’s presentation changed during her inpatient stay to be more consistent with cellulitis. If there is no clinical concern for infection, it would be appropriate to consider discontinuation of antibiotics or not beginning antibiotics initially in the ED in cases of isolated frostbite.

This case is also a good example of Osborn waves, also known as the J wave, which are J-point changes in the RS segment of the EKG [12]. In this particular case, the Osborn waves are appreciated in leads I, aVL, and V2. When present, these waves are typically appreciated in patients with core body temperatures below 32°C [12]. They are possibly due to repolarization abnormalities caused by increased outward potassium current [12]. Heukelom describes Osborn waves in a case presentation as well, stating that they are typically seen in leads II, III, aVF, and V3-V6 [13]. They also write that these waves are produced as a consequence of transmural voltage gradient differences due to changes in outward currents between the epicardium and endocardium [13]. Sources disagree on whether Osborn waves are a reliable predictor of mortality [13,14].

Having thorough knowledge of hypothermia and its range of complications is imperative in the ED, as it changes how care is conducted. Being able to establish the correct protocol and recognize expected versus unexpected complications is needed to provide appropriate standards of care. These complications can be potentially life-threatening and must be considered while examining and treating the hypothermic patient.

Conclusions

Hypothermia is a multifactorial condition that takes ambient temperature, age, sex, past medical history, and region all into account and is a common presentation in EDs. This case demonstrates Osborn waves and rewarming risks in moderate hypothermia, emphasizing the importance of exercising caution while rewarming. In the case of our patient, she had been outside overnight with a temperature low of 35°C, and the patient was noted to be in a state of moderate hypothermia at 28.3°C. Given this level of hypothermia, the patient received active rewarming with warm IV fluids, warm blankets, and an attempted Bair Hugger. Because the extremities were not left exposed when the Bair Hugger was applied, peripheral vasodilation occurred, causing hypotension that improved with removal of the Bair Hugger and continued fluid resuscitation. This is a potentially fatal complication, and hypothermia is thus a condition that all emergency physicians must understand to maintain safety during resuscitation.