Rewarming Methods in Hypothermia

Aka: Rewarming Methods in Hypothermia, Rewarming in Hypothermia, Passive Rewarming, Active External Rewarming, Minimally Invasive Active Core Rewarming, Invasive Active Core Rewarming, Core Temperature Afterdrop

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II. Approach

  1. See Hypothermia Management for protocol on using these rewarming techniques

III. Precautions

  1. Core Temperature Afterdrop
    1. Initial, abrupt core Temperature drop (as much as 7.2 C) may occur despite rewarming
    2. Due to peripheral vasodilation response to rewarming, or shunting of warming core to cooler periphery
    3. Continue rewarming per protocol and afterdrop to resolve as rewarming to continue
    4. Afterdrop may increase risk of Arrhythmia (e.g. Ventricular Fibrillation) by dropping core Temperature <32 C
      1. Despite this risk, rewarming should NOT be delayed and should be initiated in the field
    5. References
      1. Swaminathan, Shoenberger and Weingart (2023, October) EM:Rap, accessed 10/12023

IV. Management: Passive External Rewarming

  1. Goals
    1. Prevent further heat loss
  2. Efficacy
    1. Raises core Body Temperature by 0.5 to 2 C (0.9 to 3.6 F) per hour
  3. Indications
    1. Initial management for all Hypothermia patients
    2. May be sufficient alone for mild Hypothermia rewarming
    3. Relies on intact energy and Thermoregulation
    4. May begin in the field prior to arrival at hospital
  4. Technique
    1. Move the patient to warm, dry environment
    2. Protect from cold surfaces (e.g. ground, cot) with blanket or pad
    3. Remove all wet clothing
    4. Apply warm blankets
    5. Aluminum blankets or aluminized space blankets may also be used
    6. Consider covering head with hat or blanket (60% of heat loss is via head)

V. Management: Active External Rewarming

  1. Goals
    1. Directly apply heat to raise core Body Temperature
  2. Indication
    1. Initial management for all Hypothermia patients (performed simulatenously with Passive Rewarming)
    2. Relies on intact circulation
    3. Rewarm core first (as below) in serious cases
      1. Otherwise risk of adverse effects as below, including core afterdrop due to peripheral vasodilation
  3. Technique
    1. Apply hot water bottles or heating pads to trunk (chest, groin, axilla)
    2. Forced-air warming systems (e.g. Bair Hugger)
      1. Increases core Body Temperature from 0.8 C to 2.5 C per hour
      2. Preferred option in active external warming
      3. Least likey to cause adverse effects below
    3. Arteriovenous anastomosis reheating
      1. Hands immersed in 113 F (45 C) water or
      2. Device encloses Forearm in heated air at -40 mmHg
    4. External Temperature control systems (e.g. Arctic Sun)
      1. May be available in tertiary care centers (typically used for Therapeutic Hypothermia)
      2. Increases Body Temperature 0.6 to 2.5 C
    5. Warm water baths
      1. Not recommended due to inability to electronically monitor and perform other patient care
      2. However, may be considered in resource poor environments distant from referral centers
  4. Adverse effects
    1. General
      1. Patient may appear to worsen before improving
      2. Do not stop rewarming prematurely
      3. Rewarm core first in serious cases
      4. Least adverse effects with forced air rewarming
    2. Core Temperature Afterdrop
      1. Results from cold peripheral blood return as the pooled extremity blood returns to core
    3. Rewarming acidosis
      1. Redistribution of pooled peripheral Lactic Acid
    4. Peripheral vasodilation (Rewarming shock)
      1. Venous peripheral pooling

VI. Management: Minimally Invasive Active Core Rewarming

  1. Airway rewarming
    1. Warmed humidified oxygen at 104-114.8 F (40-46 C)
    2. Does not significantly increase core Temperature (but does prevent further heat loss)
      1. Previously described as increasing core temp by 1.8-4.5 F (1.0-2.5 C)/hour
  2. Intravenous Fluids
    1. Warmed saline to 38 C (100.4 F)
      1. Some guidelines describe reheating fluids to 107.6 to 114.8 F (42 to 46 C)
      2. Some other guidelines recommend heating to 43 C (109 F)
      3. Normal Saline is preferred (Lactic Acid in LR will not be metabolized by cold liver)
    2. Heat in blood warmer, warming infusion pump, blanket warmer or calibrated microwave (2 to 2.5 min on high power)
      1. Do not heat blood to >107.6 F (42 C)
      2. Do not microwave dextrose solutions
      3. Do not warm fluids in glass containers

VII. Management: Invasive Active Core Rewarming - Extracorporeal blood warming (ECMO)

  1. See Hypothermia Management
  2. Indications (Preferred method with best outcomes)
    1. Hypothermia (core Temperature <32 C or 89.6 F) and cardiac instability (including Cardiac Arrest)
    2. Systolic Blood Pressure <90 mmHg
    3. Ventricular Arrhythmia (including Asystole)
    4. Core Temperature <28 C (82.4 F)
  3. Modalities
    1. Cardiopulmonary bypass
    2. Arteriovenous or venovenous rewarming
    3. Hemodialysis
  4. Efficacy
    1. Preferred method with best outcomes
    2. Raises core Temperature by 3.6 - 10.8 F (2 to 6 C) per hour
    3. Best evidence of any intervention in severe Hypothermia
      1. Pulseless hypothermic patients have 50% survival with ECMO (esp. if ECMO Center <6 hours away)
      2. Contrast with 10% survival rate in pulseless arrest Hypothermia treated without ECMO
      3. Walpoth (1997) N Engl J Med 337(21): 1500-5 [PubMed]
      4. Ruttman (2007) J Thorac Cardiovasc Surg 134(3): 594-600 [PubMed]

VIII. Management: Invasive Active Core Rewarming - non-ECMO methods (second line)

  1. Body cavity rewarming
    1. Indicated if extracorporeal warming not available within 6 hours
    2. Less effective than other measures given small surface area of Stomach and Bladder
    3. Raises core temp by 1.8 - 2.7 F (1-1.5 C)/hour
    4. Modalities
      1. Bladder lavage (preferred)
      2. Other methods with risk or difficult administration (Gastric Lavage, Colonic lavage)
  2. Closed Thoracic Lavage
    1. See Closed Thoracic Lavage
    2. Consider in hypothermic, pulseless arrest (Hypothermia stage 4) if extracorporeal warming not available within 6 hours
    3. Raises core temp by 5.4 to 10.8 F (3 to 6 C) per hour
    4. Heated Normal Saline to 100.4 to 113 F (38 to 45 C)
    5. Administered via 2 Chest Tubes placed in left chest
      1. In (anterior, 14 Fr pigtail): Midclavicular Thoracostomy tube (second to third intercostal space)
        1. Crystalloid passes through blood warming device
        2. Continuous Infusion via Level 1 Infuser into pigtail catheter
      2. Out (posterior, 32-36 Fr Chest Tube): Midaxillary Thoracostomy tube (fourth to fith intercostal space)
        1. Output to Pleur-evac or similar device
  3. Endovascular Temperature Control Device
    1. Large central venous catheter placed at femoral vein
    2. Catheter passes blood through device for warming and then back into circulation
    3. Rewarms at rates as high as 9 F (5 C) per hour

IX. Management: Invasive Active Core Rewarming - non-ECMO methods (rarely used)

  1. Peritoneal Dialysis (Peritoneal Lavage)
    1. Consider in hypothermic, pulseless arrest if extracorporeal warming not available within 6 hours
    2. Raises core temp by 3.6 - 7.2 F (2 to 4 C) per hour
    3. Technique
      1. Instill fluid 10-20 ml/kg up to 2 Liters at 104-107.6 F (40 C to 42 C) via catheter
      2. Drain after 20 minutes
      3. Repeat throughout rewarming period
      4. Fluid options
        1. Normal Saline
        2. Lactated Ringers
        3. Dialysate solution
  2. Open thoracic lavage
    1. Consider in hypothermic, pulseless arrest if extracorporeal warming not available within 6 hours
    2. Direct lavage after thoracotomy
    3. Increases core temp by 14.4 F (8 C)

X. References

  1. Weingart and Swadron in Swadron (2023) EM:Rap 23(4): 2-4
  2. Civitarese and Sciano (2018) Crit Dec Emerg Med 32(2): 3-16
  3. Danzl in Marx (2002) Rosen's Emergency Med, p. 1979-96
  4. Danzl in Auerbach (2001) Wilderness Med, p. 135-77
  5. McCullough (2004) Am Fam Physician 70:2325-32 [PubMed]

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