2. Hypothermia (and Frostbite)

Quick Recap

Environmental System, Protocol 2/4. The full staged hypothermia management framework (Swiss staging, rewarming techniques, ECMO thresholds, "not dead until warm and dead" principle) is covered in complete detail in the Near Drowning protocol (Trauma System, Section 5), since drowning and hypothermia frequently co-occur and share an identical management algorithm. This protocol cross-references that framework and adds non-drowning-specific content: frostbite/cold tissue injury and urban/exposure hypothermia risk factors.

1. Cross-Reference — Core Staging and Rewarming Framework

See the Near Drowning protocol (Trauma System, Section 5) for the complete staged hypothermia management table, covering:

• Mild (32-35C): conscious, shivering — passive rewarming
• Moderate (28-<32C): impaired consciousness, no shivering — active external rewarming, cardiac monitoring
• Severe (24-<28C): unconscious, vital signs present — intubation, extracorporeal rewarming if available
• Profound (<24C): no vital signs — CPR, defibrillation, epinephrine per the "not dead until warm and dead" principle
• The trunk-before-extremities rewarming technique to avoid the after-drop phenomenon
• Withholding cardioactive drugs and defibrillation attempts until core temperature reaches 30C
• ECMO/cardiopulmonary bypass as the rewarming method of choice for cardiac arrest with core temp <30C and/or hyperkalemia
• Investigation for underlying infection or endocrine derangement (myxedema, adrenal insufficiency) if temperature fails to respond to warming

All of this framework applies IDENTICALLY regardless of whether hypothermia occurred with or without concurrent drowning — the physiology and management algorithm are the same; only the precipitating exposure context differs.

2. Non-Drowning Hypothermia Risk Factors and Context

Urban/exposure hypothermia: homelessness, alcohol/substance intoxication (impaired shivering response and behavioral self-protection, plus alcohol-induced peripheral vasodilation), psychiatric illness with impaired self-care, extremes of age (elderly with reduced thermoregulatory reserve and often blunted symptom recognition; infants with high surface-area-to-mass ratio), prolonged surgical exposure/anesthesia (see the Postoperative Shock protocol, Surgical ICU System, for the perioperative hypothermia discussion), trauma with prolonged extrication or exposure, and any condition impairing consciousness/mobility that prevents self-rescue from a cold environment.

Medications and conditions that blunt the normal physiologic response to cold: sedatives, antipsychotics, beta-blockers (blunted tachycardic/shivering response), hypothyroidism/myxedema, adrenal insufficiency, hypoglycemia — actively screen for these as both PRECIPITATING and CONFOUNDING factors, particularly per the Near Drowning protocol's instruction to consider myxedema/adrenal insufficiency when temperature fails to respond to standard rewarming.

All injured/trauma patients are susceptible to hypothermia, and ANY degree of hypothermia can be detrimental — hypothermia must be actively recognized during the primary survey of any trauma patient (see Polytrauma protocol, Trauma System) regardless of whether cold exposure was the primary mechanism of injury, since it commonly develops secondarily from exposure during extrication/transport, cold IV fluid administration, and evaporative losses during resuscitation.

Any stage of hypothermia can cause coagulation abnormalities, complicating resuscitation in a trauma or bleeding patient — part of the "lethal triad" (hypothermia, acidosis, coagulopathy) emphasized throughout the Hypovolemic Shock and Polytrauma protocols.

3. Frostbite and Cold Tissue Injury — Distinct from Systemic Hypothermia

Frostbite = localized tissue freezing injury, distinct from (though often co-occurring with) systemic hypothermia — requires its own specific assessment and management approach.

Assessment principle: physical estimation of injury depth and tissue damage is NOT usually accurate until demarcation between live and dead tissue becomes evident, which often requires SEVERAL WEEKS TO MONTHS of observation — avoid premature depth/severity pronouncements or early aggressive debridement based on initial appearance alone. Triple-phase bone scan may help identify the level of injury sooner than waiting for physical demarcation to fully develop, where available.

Management:

• Thrombolytics may be considered in patients presenting within 24 hours of injury — most effective when delivered as part of an established institutional protocol rather than an ad hoc, one-off decision
• For tissue cyanosis, CT angiography can assess distal perfusion
• Systemic empiric antibiotics are NOT indicated — reserve for identified/confirmed infections, not prophylaxis
• Keep wounds clean; leave uninfected blebs INTACT for up to 7-10 days, since they function as a sterile biologic dressing protecting underlying epithelialization — do not reflexively debride or unroof blisters
• Withhold tobacco, nicotine, and other vasoconstrictive agents/substances — directly worsens tissue perfusion in an already compromised extremity
• Dress wounds regularly with a local topical antiseptic to prevent bacterial colonization; debride ONLY once demarcation has clearly developed
• Early surgical debridement or amputation is SELDOM necessary unless infection occurs — a genuine departure from the more aggressive early-intervention instinct that might apply to other forms of tissue necrosis; the watch-and-wait-for-demarcation approach is the standard, evidence-supported strategy specifically for frostbite

4. Immediate Stabilization (ABCDE)

Checklist:

5. Investigations

Core temperature (esophageal, bladder, or rectal — accidental hypothermia should be measured by one of these routes, not peripheral/oral, which are unreliable at low temperatures), ECG (Osborn/J waves, arrhythmia screening), coagulation panel (hypothermia-associated dysfunction), electrolytes, glucose, thyroid function/cortisol if rewarming fails to progress, CT angiography for frostbite with tissue cyanosis, triple-phase bone scan for frostbite depth assessment where available.

6. Organ Support

Staged rewarming per the Near Drowning protocol's framework; ECMO for severe hypothermic cardiac arrest per the same criteria; standard ICU supportive care; frostbite-specific wound care (intact bleb preservation, antiseptic dressing, delayed debridement) and thrombolytic consideration within the 24h window where protocolized.

7. Consultation Matrix

8. Monitoring Framework

Continuous core temperature during active rewarming, continuous cardiac monitoring, coagulation panel trend, frostbite wound/demarcation surveillance over the extended (weeks-to-months) observation window, watch for rewarming-associated hypotension/arrhythmia.

9. Complications

After-drop phenomenon from incorrect rewarming sequencing, hypothermia-associated coagulopathy, arrhythmia during rewarming, frostbite tissue loss if prematurely debrided or infected, missed underlying endocrine/infectious cause of poor rewarming response. Prevention: trunk-first rewarming technique, appropriate ECMO threshold application, frostbite watch-and-wait approach with bleb preservation, screening for confounding endocrine causes. Rescue: extracorporeal rewarming for refractory cases, thrombolytics for early-presenting frostbite, standard arrhythmia/coagulopathy management.

10. Escalation & De-escalation

Escalate: hypothermic cardiac arrest with core temp <30C -> ECMO/extracorporeal rewarming; frostbite presenting within 24h with tissue cyanosis -> thrombolytic consideration per institutional protocol.

De-escalate: core temperature normalized without arrhythmia, frostbite demarcation clearly established with no infection -> standard wound care, staged debridement only as indicated, transition to standard monitoring.

11. ICU Discharge Criteria

Core temperature normalized and stable, no ongoing arrhythmia/coagulopathy, frostbite wounds stable with an appropriate long-term observation/debridement plan, underlying precipitant (exposure, intoxication, endocrine) addressed.

12. Documentation & Medicolegal Checklist

13. Key Guidelines

American College of Surgeons. Advanced Trauma Life Support, 11th Edition Course Manual, 2023 (Chapter 9: Thermal Injuries, Hypothermia and Frostbite sections). Brown DJ, Brugger H, Boyd J, Paal P. Accidental hypothermia. N Engl J Med. 2012;367(20):1930-1938.

14. Controversies

The precise timing window and patient selection criteria for frostbite thrombolytic therapy (commonly cited within 24h) continues to be refined, and protocolized institutional pathways vary. The threshold and modality for extracorporeal rewarming access (peripheral vs central cannulation, timing relative to ongoing CPR) in profound hypothermic arrest involves institution-specific logistics and expertise.

15. References

1. American College of Surgeons. Advanced Trauma Life Support, 11th Edition Course Manual, 2023 (Chapter 9).
2. Dureja J, Singh H, Singh S. Heat Stroke and Hypothermia. ICU Protocols: A Step-wise Approach, 2nd ed. Springer; 2020 (Ch. 17).
3. Brown DJ, Brugger H, Boyd J, Paal P. Accidental hypothermia. N Engl J Med. 2012;367(20):1930-1938.

See also: Near Drowning (Trauma System) for the complete staged hypothermia rewarming framework this protocol builds upon; Polytrauma and Hypovolemic Shock (Trauma/Cardiovascular Systems) for the "lethal triad" hypothermia-coagulopathy-acidosis interaction in trauma.