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    Accidental Hypothermia

    Environmental Injuries / Exposures

    Last Updated May 11, 2021
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    By Julian Marsden, Doug Brown, Ellie Bay

    Context

    • Accidental hypothermia (HT) = involuntary core body temperature < 35o
    • Primary HT is due to environmental exposure.
    • Secondary HT is a result of predisposing factors (e.g., alcohol/drug intoxication, trauma, shock, endocrine/metabolic, medications, burns etc.).
    • Approximately 26 HT-related deaths per year in BC (1998-2012).
    • Highest mortality rates in rural areas, lower socioeconomic status, and elderly in BC.
    • The neuroprotective effect of HT translates to the potential for the good neurologic outcomes if HT precedes brain hypoxia, even in the context of prolonged CPR and transport.
    • “No one is dead until warm and dead” still applies.

    Diagnostic Process

    Hypothermia can be assumed if the following 2 conditions are met:

    1. Cold exposure OR predisposing factor to HT, AND
    2. Trunk is cold to touch OR core temperature < 35oC

    Core Temperature

    • Core temperature needs to be measured with a low-reading thermometer.
      • Intubated patients – esophageal probe (lower third of esophagus).
      • Non-intubated patients – rectal probe (15 cm deep) or bladder probe.

    Staging

    See BC Guidelines, Table 1: Staging and Treatment of Accidental Hypothermia

    • HT I (Mild) – the patient is conscious and shivering with a core T between 35-32o
    • HT II (Moderate) – the patient has an impaired level of consciousness, they may be shivering, and their core T is <32-28o
    • HT III (Severe) – the patient is unconscious but vital signs are present with a core T <28o
    • HT IV (Hypothermic cardiac arrest) – no vital signs, and core T <28o
    • Clinical features do not always align with specific core temperatures; consider secondary causes or alternative processes when significant discrepancies.

    Investigations

    Labs selection will depend on the clinical situation but usually order:

    • Point-of-care glucose testing (all HT patients)
    • ECG (HT II-III)

    NOTE:

    • Blood samples are warmed before analyzed – masks coagulopathy of HT.
    • Blood gas analyzers warm sample to 37oC – Alpha stat strategy recommended: titrate ventilation to a PCO2 of 40mmHg (do not apply correction factors but be aware that the cold patient has a higher pH and lower partial pressures compared with the results from your warmed samples).

    Patients in Cardiac Arrest

    • HT can be ruled out as the cause of cardiac arrest when:
    • Absent vital signs and normothermic cardiac arrest prior to cooling.
    • Absent vital signs, asystole, and core temperature >32oC.

    Recommended Treatment

    Handle hypothermic patients carefully throughout assessment due to risk of arrhythmias.

    ABCs

    • Assess signs of life for 60 seconds through clinical examination and other modalities if available (ECG, EtCO2 and ultrasound).
      • Check central pulse.
      • Do not assume death or poor neurologic prognosis in hypothermic patients with fixed dilated pupils, absent corneal reflexes, signs of rigor mortis, areflexia, and/or respiratory arrest.
    • Look for other injuries (e.g., frostbite, trauma).

    Triage

    See BC guidelines, Appendices: A. Management of Accidental Hypothermia, B. EPOS Triage Tool for Stage IV Accidental Hypothermia, C. EPOS Triage Tool for Stage III Accidental Hypothermia, D. Provincial ECMO Provider Map.

    • HT I – manage on-site or transport to hospital particularly if suspected secondary HT.
    • HT II – transport to hospital (ideally ECMO/Cardiopulmonary bypass (CPB) center).
    • HT III, IV – contact Emergency Physician Online Support (EPOS) – BC Patient Transfer Network (BCPTN) or BCAS dispatch for consideration of transfer to ECMO/CPB-capable center or a portable ECMO team may be dispatched.
    • If history suggests cardiac arrest prior to hypothermia – Either use local Termination of Resuscitation Protocols (BCAS – EPOS) or transport to nearest hospital.

    Transport Considerations

    • Consider a mechanical CPR device if in cardiac arrest.
    • Prevent further heat loss.
    • If transport time to ECMO/CPB is >6 hours, the patient will likely be managed locally.

    Rewarming Techniques

    • Passive rewarming: prevent heat loss and support self-rewarming.
      • Warm environment, dry clothes, insulation, warm drinks, active movement
    • Active external and minimally invasive rewarming: provide heat to body surface.
    • Active internal/invasive rewarming: provide heat to body’s interior. Examples:
      • Extracorporeal life support (VA-ECMO or CPB)
      • Warm (38-42oC) lavage (e.g. bladder, thoracic, peritoneal)
      • Indications for invasive vascular rewarming techniques that do not support circulation are not well established.
    • Hot showers/baths are not recommended as risk of hypotension.

    Management Based on Stage

    See BC Guidelines, Table 1: Staging and Treatment of Accidental Hypothermia, Appendix A: Management of Accidental Hypothermia, Appendix E: Practical Tips for Rewarming HT II & III.

    • HT I – passive rewarming
      • Treat as HT II in cases of trauma, comorbidities, or possible secondary hypothermia.
    • HT II – active external and minimally invasive rewarming; cardiac and core temp monitoring.
    • HT III – active external and minimally invasive rewarming; cardiac and core temp monitoring; +/-airway management; +/- bladder lavage.
      • Cardiac stability – invasive rewarming not recommended
      • Refractory cardiac instability – consider ECMO/CPB
    • HT IV – CPR; airway management; ECMO/CPB (ideally).
      • There is a lack of consensus in various guidelines (ERC, AHA, BC) but BC guidelines recommend up to three doses of epinephrine and defibrillation with additional doses guided by response.
      • Alternative to ECMO/CPB – continue CPR; rewarm to 32oC with active external and internal rewarming (+/- bladder lavage, +/- thoracic lavage, +/- peritoneal lavage).
      • Do not apply heat to the patient’s head.

    Important Considerations

    • Rewarming will likely correct the following:
      • Acid-base disturbances (bicarbonate in not recommended unless other indications are present)
      • Benign arrhythmias (atrial fibrillation and flutter, bradycardia, AV blocks, nodal rhythms, QRS prolongation)
      • Mild hypotension
    • Vasopressors – increased risk of arrhythmias with early administration. Consultation recommended.
    • Sedatives, analgesics – suppress adaptive physiologic responses (e.g., shivering, vasoconstriction).
    • Risk of drug toxicity in hypothermic patients due to reduced metabolism of drugs.
    • Keep central venous catheter tips away from heart.
    • If inadequate response to rewarming, think of secondary causes.

    Prognostication and Resuscitation Termination

    • European Resuscitation Council (ERC) Guidelines 2021 recommend using either the HOPE or ICE score for prognostication of successful extracorporeal life support (ECLS) rewarming. ERC advises against the use of these scores in children.
    • Termination of resuscitation may be considered in patients with HT IV if serum potassium is >12mmol/L, or if the patient is rewarmed to ≥32oC and on-going asystole and no other causes of reversible cardiac arrest.
      • Serum potassium – may be less reliable than HOPE or ICE scores; risk of false elevations with comorbidities or certain medications.

    Complications of hypothermia

    Early:

    • Cardiac – dysrhythmias (e.g. VF), cardiac arrest
    • Neurologic – CNS impairment
    • Metabolic – cold diuresis, rhabdomyolysis, pseudo-rigor mortis
    • Hematologic – coagulopathy, hypercoagulable state
    • Extracorporeal life support-related complications

    Late (post-rewarming):

    • Respiratory – pulmonary edema, infection, respiratory arrest
    • Cardiac – hypotension, dysrhythmias, cardiac stunning
    • Neurologic – seizures, peripheral neuropathy, impaired cognition, coma
    • Multi-organ failure

    Quality Of Evidence?

    Justification

    Indications for the administration of epinephrine in hypothermic cardiac arrest patients – Mostly based on animal studies and conflicting recommendations among various guidelines. – Low.

    The HOPE Score – Derived from a systematic literature review (18 studies, 237 patients) and unpublished hospital data (49 patients). This score has been externally validated. – Low.

    ICE Survival Score – Derived from an individual patient data meta-analysis of observational studies (44 retrospective cohort studies, 40 case reports). This model has not been validated. – Low.

    Low

    Related Information

    Reference List

    1. Brown DJ, British Columbia Accidental Hypothermia Working Group. Accidental hypothermia clinical practice guideline for British Columbia. Published December 9, 2016. Accessed April 19, 2021.


    2. Brown DJA, Brugger H, Boyd J, Paal P. Accidental Hypothermia. NEJM. 2012;367:1930-1938. doi:10.1056/NEJMra1114208.


    3. Paal P, Gordon L, Strapazzon G, et al. Accidental hypothermia – An update. Scand J Trauma Resusc Emerg Med. 2016;24:111. doi:10.1186/s13049-016-0303-7.


    4. Brown DJA. Hypothermia. In: Tintinalli JE, Ma OJ, Yealy DM, Meckler GD, Stapczynski JS, Cline DM, Thomas SH, eds. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 9th McGraw-Hill; 2020. Accessed April 21, 2021.


    5. Stares J, Kosatsky T. Hypothermia as a cause of death in British Columbia, 1998-2012: A descriptive assessment. CMAJ Open. 2015;3(4):E352-E358. doi:10.9778/cmajo.20150013.


    6. Zafren K, Mechem CC. Accidental hypothermia in adults. In: Post, TW, ed. UpToDate. Waltham, MA: UpToDate; 2021. Accessed April 22, 2021.


    7. Lott C, Truhlář A, Alfonzo A, et al. European Resuscitation Council Guidelines 2021: Cardiac arrest in special circumstances. Resuscitation. 2021;161:152-219. doi: 10.1016/j.resuscitation.2021.02.011.


    8. Pasquier M, Rousson V, Darocha T, et al. Hypothermia outcome prediction after extracorporeal life support for hypothermic cardiac arrest patients: An external validation of the HOPE score. Resuscitation. 2019;139:321-328. doi: 1016/j.resuscitation.2019.03.017.


    9. Pasquier M, Hugli O, Paal P, et al. Hypothermia outcome prediction after extracorporeal life support for hypothermic cardiac arrest patients: The HOPE score. Resuscitation. 2018;126:58-64. doi:10.1016/j.resuscitation.2018.02.026.


    10. Saczkowski RS, Brown DJA, Abu-Laban RB, Fradet G, Schulze CJ, Kuzak ND. Prediction and risk stratification of survival in accidental hypothermia requiring extracorporeal life support: An individual patient data meta-analysis. Resuscitation. 2018;127:51-57. doi:10.1016/j.resuscitation.2018.03.028.


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