Evidence-Based Management Of Accidental Hypothermia In The Emergency Department

Table of Contents

 

1. Abstract
2. Case Presentations
3. Introduction
4. Critical Appraisal of the Literature
5. Etiology And Pathophysiology
6. Differential Diagnosis
7. Prehospital Care
   1. Field Assessment
8. Emergency Department Evaluation
   1. History
   2. Physical Examination
      1. Mental Status
      2. Vital Signs
         • Temperature
         • Pulse
         • Blood Pressure
         • Respiratory Rate
         • Pulse Oximetry
      3. Neurologic Examination
      4. Other Physical Examination Findings
9. Diagnostic Studies
   1. Laboratory Studies
      1. Fingerstick Glucose
      2. Chemistry Panel
      3. Complete Blood Count
      4. Coagulation Studies
      5. Blood Gases
      6. Other Laboratory Testing
   2. Imaging Studies
      1. Plain Films
      2. Ultrasound
      3. Computed Tomography
   3. Other Diagnostic Studies
      1. Electrocardiography
10. Treatment
11. Controversies
    1. Core Afterdrop
12. Disposition
13. Special Circumstances
    1. Hypothermia In Trauma Patients
14. Summary
15. Risk Management Pitfalls For Accidental Hypothermia
16. Time- And Cost-Effective Strategies
17. Case Conclusions
18. Clinical Pathway For Managing Accidental Hypothermia
19. Tables and Figures
    1. Table 1. Risk Factors For Thermoinstability And Secondary Hypothermia
    2. Figure 1. Electrocardiogram Of A Hypothermic Patient With Prominent J Waves (Osborn Waves)
20. References

Abstract

Accidental hypothermia is defined as an unintentional drop in core body temperature below 35°C. It can present in any climate and in any season, as it is not always a result of environmental exposure; underlying illnesses or coexisting pathology can play important roles. Although there is some variability in clinical presentation, hypothermia produces a predictable pattern of physiologic responses and clinical manifestations, and effective treatment has yielded many impressive survival case reports. Treatment strategies focus on prevention of further heat loss, volume resuscitation, implementation of appropriate rewarming techniques, and management of cardiac dysrhythmia. Rewarming may be passive or active and/or internal or external, depending on severity and available resources. This issue focuses on methods of effective rewarming and prevention of further morbidity and mortality.

Case Presentations

Emergency physicians in 3 different cities encounter 3 distinct patients with 1 thing in common: a low core body temperature.

Introduction

Accidental hypothermia is defined as the unintentional drop in core body temperature below 35°C (95°F).¹ While accidental hypothermia is most common in cool climates during winter months, it can also occur in warm climates, in any season, and in individuals without a history of outdoor exposure. Accidental hypothermia can occur in a variety of populations, including those in an urban environment. Those at highest risk include homeless individuals, the very young and very old, and individuals with psychiatric disease, serious underlying medical conditions, traumatic injuries, or drug or alcohol intoxication.^2,3 These groups often have impaired thermoregulation, but they also lack the ability to perform the behavioral adaptations to protect themselves from the cold, such as seeking shelter and putting on extra clothing.

The United States Centers for Disease Control and Prevention (CDC) reported that in the United States during the years of 1999 to 2011, there were an average of 1301 deaths from environmental cold exposure per year.⁴ Approximately half of the deaths attributed to hypothermia occur in patients over the age of 65. Inhospital mortality of patients with moderate or severe hypothermia is as high as 40%.³ Despite the high mortality rate, there have been survivors with good neurologic outcomes who were resuscitated from extremely low temperatures, the lowest of which was 13.7°C.⁵ There have also been case reports of individuals surviving neurologically intact after prolonged cardiac arrest, the longest being in cardiac arrest for 8 hours and 40 minutes.⁶

In this issue of Emergency Medicine Practice, we will review the definition, pathophysiology, differential diagnosis, prehospital management, and emergency department (ED) evaluation and management of patients presenting with accidental hypothermia.

Critical Appraisal Of The Literature

Risk Management Pitfalls For Accidental Hypothermia

1. “I work in Florida, not Alaska. I didn’t think I’d ever see a hypothermic patient.”
   While most cases of accidental hypothermia occur in colder climates during the winter months, hypothermia can occur anywhere, including mild climates. All emergency clinicians should have the skills to identify and treat these patients.
2. “The nurse couldn’t get a temperature.”
   Normal thermometers only read down to 34°C. If a thermometer is not reading appropriately, it may be because the patient’s core body temperature is below that level. A low-reading thermometer should be used to obtain a core body temperature and assess for hypothermia.
3. “I couldn’t feel a pulse, so we started CPR.”
   Pulses are extremely difficult to palpate in hypothermic patients. Additionally, initiating CPR in hypothermic patients with a perfusing rhythm runs the theoretical risk of precipitating a nonperfusing dysrhythmia that is refractory to treatment. If possible, bedside cardiac ultrasound or cardiac monitoring should be used to evaluate for organized cardiac activity. If that is not available, the emergency clinician should palpate for a pulse for a full minute before initiating CPR.
4. “I started rewarming the patient and then admitted him to the ICU. As the patient was going upstairs, he arrested in the elevator.”
   A moderately or severely hypothermic patient’s clinical status is extremely tenuous. Dysrhythmias and cardiovascular collapse can occur at any time, often after rewarming has been initiated. Strongly consider limiting any transport within the hospital until the patient is rewarmed to 30°C to 32°C (with the clear exception of transport to the operating room for cardiopulmonary bypass). Patients who must be transported prior to rewarming will need ongoing cardiac monitoring and, ideally, should be transported in the company of the treating physician.
5. “I put warm blankets on him and started IV fluids. I don’t know why his temperature hasn’t improved.”
   If passive external rewarming fails in mild hypothermia, turn to more aggressive rewarming measures, but also begin to investigate reasons why the patient is not rewarming as expected. Underlying infection is a common cause of slowed or failed rewarming, and individuals who fail to rewarm should be treated empirically with antibiotics.⁴⁵
6. “His pupils were fixed and dilated, so I thought he would have a bad outcome.”
   Fixed and dilated pupils can be seen at temperatures below 27°C and are expected by the time a patient reaches a core temperature of 22°C.¹⁴ While alternate causes of decreased cerebral perfusion should be considered, it is possible that this finding is due solely to hypothermia, and is not necessarily indicative of a poor neurologic outcome.
7. “I didn’t think he needed fluids because his heart rate was normal.”
   “Normal“ vital signs in a hypothermic patient are, typically, not normal. In a moderately hypothermic patient, bradycardia is expected. The presence of a normal heart rate should be perceived as relative tachycardia, and an etiology should be sought and the patient treated. Hypovolemia is often present in hypothermic individuals and should be treated with warm IV fluids.
8. “I didn’t see any evidence of hyperkalemia on his ECG.”
   Typical ECG changes seen with hyperkalemia are blunted in hypothermia. Acute renal failure and rhabdomyolysis are common in hypothermic patients and can lead to severe hyperkalemia. Despite a nondiagnostic ECG, keep a high index of suspicion for hyperkalemia both on presentation and during their ED course, as potassium levels can fluctuate rapidly during rewarming.
9. “Just after I examined the patient’s extremities for frostbite, he had a ventricular fibrillation arrest.”
   Extreme care should be taken when moving and examining a patient with moderate or severe hypothermia. Movement of a patient’s extremities may increase the return of cold blood to central circulation, causing a further drop in temperature and placing a patient at further risk for hemodynamic instability and cardiac arrest. While this should not prevent you from completing necessary tasks (eg, intubation), the treatment team should try to minimize any extraneous movement or jostling until a patient is rewarmed.
10. “The patient was in asystole and didn’t respond to multiple rounds of epinephrine, so we called the code.”
    The adage, “a patient is not dead until he is warm and dead” still holds true. Resuscitation of a hypothermic cardiac arrest patient should be continued until the patient is adequately rewarmed, as individuals with extremely low core temperatures who are given prolonged CPR can have good neurologic outcomes. Ventricular fibrillation may be refractory to defibrillation until a patient is sufficiently rewarmed. If a patient remains pulseless at 32°C, resuscitation efforts may then be terminated.

Tables And Figures

References

Evidence-based medicine requires a critical appraisal of the literature based upon study methodology and number of subjects. Not all references are equally robust. The findings of a large, prospective, randomized, and blinded trial should carry more weight than a case report.

To help the reader judge the strength of each reference, pertinent information about the study are included in bold type following the reference, where available. In addition, the most informative references cited in this paper, as determined by the authors, will be noted by an asterisk (*) next to the number of the reference.

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