Emergency & Toxicology

Hypothermia and frostbite: management

Clinical Overview and When to Suspect Hypothermia and Frostbite

— Mild: 32–35°C (shivering, tachycardia, vasoconstriction)

— Moderate: 28–32°C (shivering stops, bradycardia, AMS, "paradoxical undressing")

— Severe: <28°C (coma, fixed pupils, apnea, VF risk, may mimic death)

— Any prolonged cold exposure (homeless, intoxicated, trauma victim, immersion, avalanche, outdoor worker/recreator)

— Altered mental status + cold environment — assume hypothermia until proven otherwise

— Trauma patients with prolonged extrication — even temperate climates cause hypothermia

— Post-operative, massive transfusion, near-drowning, sepsis ("septic hypothermia" carries worse prognosis than fever)

— Endocrine: myxedema coma, adrenal crisis, hypoglycemia, Wernicke's

— Drug-induced: ethanol, benzodiazepines, opioids, phenothiazines, antipsychotics impair thermoregulation

Hypothermia = core body temperature <35°C (95°F), measured by low-reading rectal, esophageal, or bladder probe — standard thermometers miss it

Frostbite = freezing injury to tissue with ice crystal formation, most commonly in fingers, toes, ears, nose, cheeks

When to suspect:

Frostbite suspicion: any cold-exposed extremity with numbness, waxy/white skin, hard "wooden" feel, especially after wind-chill exposure or wet gear

Board pearl: "No one is dead until they are warm and dead." Continue resuscitation until core temp >32–35°C, because severe hypothermia can mimic death (fixed pupils, asystole) yet have full neurologic recovery — particularly in pediatric submersion and avalanche victims.

Step 3 management: First action in any suspected hypothermic patient = measure core temperature with a low-reading probe AND remove wet clothing + initiate passive external rewarming simultaneously. Don't anchor on a normal-range tympanic reading.

Presentation Patterns and Key History

— Duration and nature of exposure: dry vs wet (immersion accelerates heat loss ~25x), wind chill, ambient temperature, clothing adequacy

— Time of last seen normal, found-down position, snow burial depth (avalanche)

— Substance use (ethanol is #1 cofactor in urban hypothermia — causes vasodilation + impaired shivering + impaired judgment)

— Trauma mechanism (MVC with prolonged extrication, fall)

— Comorbidities: hypothyroidism, hypopituitarism, adrenal insufficiency, hypoglycemia, malnutrition, sepsis, burns, extensive dermatologic disease, spinal cord injury (impaired vasoconstriction)

— Medications: beta-blockers, alpha-agonists, sedatives, antipsychotics

— Prior cold injury (increases susceptibility to refreezing injury)

— HT I: conscious, shivering (~32–35°C)

— HT II: impaired consciousness, no shivering (~28–32°C)

— HT III: unconscious, vital signs present (~24–28°C)

— HT IV: apparent death, no vital signs (<24°C)

— Initial numbness/clumsiness → after rewarming, throbbing pain as perfusion returns

— Prior thaw–refreeze cycles (much worse outcome than single freeze)

— Tobacco use, peripheral vascular disease, Raynaud's, prior frostbite all raise risk

— Tight footwear, wet socks/gloves

Targeted history (often from EMS, family, bystanders since patient may be obtunded):

Clinical staging (Swiss/HT system):

Frostbite history:

Frostnip vs frostbite: frostnip is superficial, fully reversible with rewarming, no tissue loss. Frostbite involves true tissue freezing.

Key distinction: Paradoxical undressing (patient found nude in cold) and terminal burrowing (crawling into enclosed spaces) are signs of severe hypothermia, not assault or psychiatric illness — important for forensic and ED documentation. Mistaking these for crime scenes delays resuscitation.

Board pearl: Ethanol intoxication + winter night + AMS = check core temp before attributing solely to intoxication; missed hypothermia in ED hallways is a sentinel event.

Physical Exam Findings and Hemodynamic Assessment

— Early: tachycardia, HTN, vasoconstriction

— Progressive: bradycardia (refractory to atropine — atrial/sinus node dysfunction from cold), hypotension

— Severe: VF, asystole; myocardium becomes irritable — minimize unnecessary movement

— Bradycardia, prolonged PR/QRS/QT

— Osborn (J) wave — positive deflection at the J point, classic at <32°C

— Atrial fibrillation (common, usually resolves with rewarming — do NOT cardiovert or anticoagulate for cold-induced AF)

— VF risk rises sharply <28°C; rough handling, central line wires near RA, or intubation can trigger it

— Grade 1: numbness/erythema, no blister — no tissue loss expected

— Grade 2: clear/serous blisters on distal phalanx — minimal tissue loss

— Grade 3: hemorrhagic blisters extending proximally — soft tissue loss

— Grade 4: hemorrhagic blisters proximal to MCP/MTP with cyanosis — bone/muscle loss, likely amputation

General: pale, cool, possibly cyanotic skin; rigid muscles; "ice cold" abdomen on palpation in severe cases

Mental status: gradient from confusion/dysarthria → stupor → coma as temperature falls

Cardiovascular:

Respiratory: initial tachypnea → bradypnea → apnea; bronchorrhea ("cold-induced")

Neuro: hyporeflexia, dilated/fixed pupils at extreme temps, mimics brain death

Pulse check: palpate for at least 60 seconds at carotid/femoral — pulses may be slow and weak; avoid premature CPR initiation if any organized rhythm with perfusion

ECG findings:

Frostbite exam after rewarming determines grade:

CCS pearl: In the CCS case, order core temperature q15min, continuous cardiac monitoring, and document all four extremity exams before and after rewarming. Move the patient gently — rough transfer can precipitate VF.

Board pearl: Osborn waves + bradyarrhythmia in a cold-exposed patient is essentially pathognomonic — don't chase ischemia workup before rewarming.

Diagnostic Workup — Initial Labs, Imaging, ECG

— Low-reading rectal/esophageal/bladder thermometer (tympanic unreliable in severe cold)

— Fingerstick glucose (hypoglycemia common and treatable)

— Continuous cardiac monitor, pulse oximetry (may read falsely from cold extremity), 12-lead ECG

— Point-of-care ultrasound (cardiac standstill confirmation in unresponsive patient)

— CBC: hemoconcentration (cold diuresis + fluid shifts); Hct rises ~2% per 1°C drop

— BMP: hyperkalemia (cell lysis, acidosis) — K >12 mmol/L in adults is generally considered incompatible with survival and used as a futility marker for prolonged resuscitation/ECMO

— Glucose: variable; hyperglycemia from impaired insulin release at <30°C, then hypoglycemia after rewarming

— ABG/VBG: acidosis common; interpret values uncorrected (machine warms blood to 37°C — use those numbers)

— Lactate, coags (cold-induced coagulopathy, often DIC picture), fibrinogen

— Lipase (cold-induced pancreatitis is real)

— CK (rhabdomyolysis), troponin, TSH, cortisol if myxedema/adrenal suspected

— Ethanol level, tox screen, salicylate/acetaminophen if AMS

— Blood cultures (sepsis cause vs effect)

— CXR for aspiration, pulmonary edema

— CT head if AMS persists after rewarming or trauma suspected

— Trauma series if mechanism warrants

Bedside immediately:

Labs:

Imaging:

Step 3 management: A K+ >10–12 mmol/L, pH <6.5, and asphyxial mechanism (avalanche with packed airway >35 min) collectively support termination of resuscitation per ERC criteria — but isolated severe hypothermia without these features mandates prolonged efforts including ECMO transfer.

Board pearl: Don't trust pulse oximetry on a frostbitten finger — use ear/forehead probe or arterial sampling.

Diagnostic Workup — Advanced or Confirmatory Studies

— Technetium-99m bone scintigraphy at 24–72 hours: identifies non-perfused tissue, guides early thrombolysis decisions and delineates amputation level

— MR angiography or CT angiography: alternative imaging for vascular patency in deep frostbite

— Digital plethysmography, infrared thermography in specialized centers

— Doppler of distal pulses pre- and post-rewarming

— TSH, free T4 (myxedema coma — coma + hypothermia + bradycardia + hyponatremia)

— Random cortisol, ACTH stim if adrenal crisis suspected

— Septic workup: cultures × 2, lactate, procalcitonin, urinalysis

— Repeat glucose, ammonia, B12, thiamine if persistent AMS

— Head CT for stroke/hemorrhage mimicking cold exposure

— Severe hypothermia (<28°C) with cardiac instability, arrest, or refractory to active rewarming

— HOPE score (Hypothermia Outcome Prediction after ECLS) estimates survival probability — uses age, sex, K+, CPR duration, asphyxia, core temp; guides triage to ECMO centers

— K+, lactate, witnessed arrest, downtime are key inputs

For frostbite — perfusion assessment after rewarming:

For hypothermia — etiology workup once stable:

ECMO/CPB candidacy assessment:

For unresponsive cold patient: bedside echo or POCUS confirms cardiac standstill before declaring asystole — true asystole vs profound bradycardia easily confused in severe hypothermia

Key distinction: Acute pulmonary edema with frothy sputum after rewarming is not always cardiogenic — consider rewarming-induced ARDS and non-cardiogenic pulmonary edema from capillary leak. Echo helps differentiate.

Board pearl: Bone scan at 48 hours is the single best predictor of frostbite tissue viability and the trigger for late surgical demarcation — avoid early amputation; "frostbite in January, amputate in July."

Risk Stratification and First-Line Management Logic

— Airway/intubation indicated for unresponsive — gentle technique; intubation does NOT routinely trigger VF despite older teaching

— Breathing: warm humidified O2 (40–46°C)

— Circulation: prolonged pulse check (60 sec); CPR if no organized rhythm or signs of life

— Move patient horizontally, avoid rough handling

— Mild (HT I, 32–35°C): passive external rewarming — remove wet clothing, dry, insulate, warm room, oral warm fluids if alert

— Moderate (HT II, 28–32°C): active external rewarming — forced-air warming blankets (Bair Hugger), heating pads to trunk only (limb rewarming first causes "afterdrop" and acidosis from peripheral vasodilation washing cold/acidic blood centrally)

— Add minimally invasive active internal: warm IV fluids (40–42°C), warm humidified O2

— Severe (HT III–IV, <28°C): active internal rewarming — bladder/gastric/pleural/peritoneal lavage with warm saline; ECMO/CPB is gold standard for arrest or instability (rewarming rate 6–10°C/hr)

— Defibrillation: 1 attempt; if no response at <30°C, resume CPR and rewarm; redefibrillate as temp rises

— Vasoactive drugs typically withheld below 30°C (ineffective + accumulate); some protocols allow with prolonged intervals (epinephrine q6–10 min) between 30–34°C

— Treat hypoglycemia, give thiamine if alcoholism/malnutrition

— Empiric hydrocortisone + levothyroxine if myxedema suspected

ABCs first, but modified for cold:

Rewarming strategy by severity:

Resuscitation modifications:

CCS pearl: Order warm IV crystalloid bolus, forced-air warmer to torso, continuous core temp, cardiac monitor, fingerstick glucose, rectal probe, and consult cardiothoracic surgery for ECMO in any HT III/IV patient — clock advances 15 min at a time, document temp trend.

Board pearl: "Afterdrop" = transient further fall in core temperature after rewarming starts; minimized by truncal-only active rewarming.

Pharmacotherapy — First-Line Regimen

— IV fluids: warmed isotonic crystalloid (40–42°C); large volumes often needed due to cold diuresis and rewarming vasodilation. Avoid lactated Ringer's in severe hypothermia — cold liver clears lactate poorly; use NS or Plasmalyte

— Dextrose for documented hypoglycemia; thiamine 100 mg IV if malnutrition/alcoholism

— Hydrocortisone 100 mg IV + levothyroxine 200–500 mcg IV if myxedema coma suspected (don't wait for TSH)

— Empiric antibiotics if sepsis suspected as cause (broad spectrum, after cultures)

— Vasopressors: norepinephrine preferred if needed >30°C; generally ineffective and accumulate <30°C

— No role for routine antibiotics in pure cold-only hypothermia

— Rapid rewarming: immerse affected part in circulating water at 37–39°C (98–102°F) for 15–30 min until thawed (soft, pliable, red/purple). Do not rewarm if refreezing is possible — refreeze causes worse injury than delayed thaw

— NSAIDs (ibuprofen 12 mg/kg/day divided BID, max 2.4 g/day): inhibits thromboxane, reduces prostaglandin-mediated vasoconstriction and tissue loss

— Tetanus update

— Opioid analgesia — rewarming is extremely painful; expect significant requirements

— Topical aloe vera every 6 hours — antiprostaglandin, weak evidence but standard

— Penicillin or amoxicillin considered in deep frostbite with streptococcal infection risk; not universal

Hypothermia — there is no "first-line drug" — rewarming is the treatment. Pharmacology is supportive and etiology-specific:

Frostbite — first-line pharmacotherapy after rapid rewarming:

Step 3 management: For deep frostbite (grade 3–4) presenting <24 hours from rewarming with no perfusion on imaging, refer for IV/IA tissue plasminogen activator (tPA) ± heparin at a specialized center — reduces amputation rates dramatically.

Board pearl: Dry rewarming, rubbing with snow, or warming over an open flame are all contraindicated — friction and uneven heat cause additional tissue damage.

Procedures and Invasive Management

— Warm IV fluids (40–42°C), warm humidified O2 — minimally invasive baseline

— Bladder lavage: warm saline via Foley, useful adjunct, slow rate

— Gastric lavage: NG/OG with warm saline — risk of aspiration; secure airway first

— Pleural lavage: 2 chest tubes (one anterior, one posterior-lateral), inflow/outflow warm saline — effective, invasive

— Peritoneal lavage: dialysis catheter with warm saline — useful when ECMO unavailable

— Hemodialysis: useful if concurrent toxicology/hyperkalemia; provides 2–3°C/hr

— ECMO/cardiopulmonary bypass: gold standard for arrest or refractory severe hypothermia, 6–10°C/hr rewarming, provides perfusion during VF

— Thrombolysis (IV/IA tPA) — within 24 hours of rewarming for grade 3–4 frostbite without contraindication; major bleeding risk so requires informed consent and ICU monitoring

— Iloprost (prostacyclin analogue) — IV vasodilator, used in Europe and increasingly in US; especially valuable when tPA contraindicated; given over 5 days

— Sympathetic blockade (stellate ganglion or lumbar) — adjunct in selected cases

— Blister management: aspirate or debride clear blisters (contain thromboxane); leave hemorrhagic blisters intact (debridement increases desiccation/infection)

— Fasciotomy for compartment syndrome (uncommon but assess compartments)

— Delayed amputation: weeks to months; let demarcation declare itself

Active internal rewarming techniques (escalating invasiveness):

Frostbite procedures:

CCS pearl: In CCS, advance the clock and reassess core temp every 15 min during active rewarming; if temp does not rise ≥1°C/hr with ECMO running or patient remains in VF after rewarming to >32°C, reconsider underlying etiology (sepsis, drug overdose, endocrine).

Board pearl: "Tissue first, then time" — preserve all marginal tissue with tPA/iloprost early; debride and amputate only after clear demarcation, typically 1–3 months later.

Special Populations — Elderly and Renal/Hepatic Impairment

— Impaired thermoregulation: reduced shivering, blunted vasoconstriction, lower baseline metabolic rate, decreased perception of cold

— Urban hypothermia is often elderly: inadequate heating, fixed income, medications (beta-blockers, antipsychotics), comorbid hypothyroidism, dementia

— Lower trigger temperatures still cause significant hypothermia (65°F home can be enough)

— Higher mortality at any given core temperature vs younger patients

— Underlying acute illness (sepsis, MI, stroke, hip fracture) is common precipitant — workup thoroughly even if cold exposure obvious

— Rewarming more gradual to avoid hemodynamic collapse; cardiac reserve limited

— Frostbite has higher amputation rates due to baseline PAD, diabetes

— Hyperkalemia risk amplified during rewarming (cell lysis + impaired excretion)

— Cold diuresis may mask true volume status; monitor closely

— Drug clearance reduced — avoid renally cleared sedatives if possible

— tPA for frostbite: ESRD not absolute contraindication but bleeding risk elevated

— Dialysis catheters can double as rewarming circuit (warm dialysate)

— Cannot clear lactate well — avoid lactated Ringer's

— Coagulopathy at baseline + cold-induced coagulopathy = additive bleeding risk

— Hypoglycemia more profound and prolonged

— Reduced metabolism of opioids/benzodiazepines used during rewarming

— Alcoholic patients: pair thiamine 100 mg IV before glucose to avoid precipitating Wernicke's

Elderly:

Renal impairment:

Hepatic impairment:

Step 3 management: Any elderly patient found down at home with core temp <35°C should have TSH, glucose, troponin, lactate, blood cultures, head CT, and CXR as part of standard workup — cold exposure is the symptom, not always the diagnosis.

Board pearl: Geriatric "indoor hypothermia" in winter months reflects social determinants — connect to LIHEAP, social work, home safety assessment before discharge.

Special Populations — Pregnancy, Pediatrics, and Other Subgroups

— Higher surface-area-to-mass ratio → faster heat loss; thin SQ fat

— Infants: minimal shivering; rely heavily on non-shivering thermogenesis (brown fat)

— Submersion in cold water: classic for excellent neurologic recovery even after prolonged arrest (mammalian dive reflex + rapid brain cooling pre-arrest) — pursue aggressive resuscitation including ECMO

— Weight-based warm fluid resuscitation (20 mL/kg boluses)

— Don't rely on shivering as a clinical marker in infants

— Watch for non-accidental injury: cold exposure can be neglect; screen and report per state law

— Maternal hypothermia → fetal bradycardia and reduced uteroplacental perfusion

— Tilt patient 15° left during resuscitation (aortocaval decompression)

— Continuous fetal monitoring once viable (>23–24 wks)

— Rewarm mother to rewarm fetus; do not attempt isolated fetal warming

— Standard hypothermia interventions including ECMO are permissible in pregnancy

— tPA for frostbite is relative contraindication in pregnancy — discuss risks; iloprost preferred when available

— Refreeze injury vastly worse than single freeze — counsel on definitive evacuation before thawing

— Wet gear/boots = 25x heat loss; teach layering, vapor barriers

— Prior frostbite increases recurrence risk — protective gear, hand/toe warmers

— Ethanol most common cofactor in urban hypothermia

— IV drug use → infection risk during prolonged ED stay; meticulous line care

— Withdrawal management during rewarming + ICU stay

— Engage SUD counseling, harm reduction, housing-first programs at discharge

Pediatrics:

Pregnancy:

Outdoor occupations/recreationalists:

Patients with substance use disorder:

Key distinction: A normothermic pediatric drowning patient has poor prognosis after >10 min submersion; a cold-water submersion (<5°C) child can recover fully even after 30–60 min — never call the code based on downtime alone.

Board pearl: Pregnancy + hypothermia = treat the mother aggressively, monitor the fetus continuously; maternal rewarming is fetal therapy.

Complications and Adverse Outcomes

— Ventricular fibrillation (rough handling, electrolyte shifts, <28°C)

— Refractory bradyarrhythmias unresponsive to atropine/pacing until rewarmed

— Rewarming-induced hypotension (vasodilation, "rewarming shock")

— Asystole; "stunned myocardium" post-arrest

— Aspiration pneumonia (depressed gag reflex)

— Non-cardiogenic pulmonary edema / ARDS during rewarming

— Pulmonary embolism (cold-induced hypercoagulable state in some)

— Bronchorrhea

— Acute tubular necrosis from rhabdomyolysis (frozen muscle)

— Cold diuresis → severe hypovolemia at rewarming

— Hyperkalemia (rewarming, cell lysis) — life-threatening

— Acidosis (lactic + respiratory)

— Hypo/hyperglycemia

— Rebound hyperthermia after aggressive warming

— DIC, cold-induced coagulopathy (enzyme dysfunction reversed by rewarming)

— Thrombocytopenia (splenic sequestration)

— Hemoconcentration → thrombosis risk

— Stress ulceration, GI bleeding

— Pancreatitis (cold-induced)

— Ileus

— Anoxic brain injury if prolonged arrest

— Persistent vegetative state

— Peripheral neuropathy (cold neuritis) — chronic pain, paresthesias post-frostbite

— Amputation (most feared; correlated with depth + delay to care)

— Chronic pain, hyperhidrosis, hypersensitivity to cold (Raynaud-like)

— Nail dystrophy, growth plate injury in children → premature epiphyseal closure → growth disturbance

— Skin atrophy, hyperpigmentation, squamous cell carcinoma at chronic frostbite scars (Marjolin-like)

— Compartment syndrome

— Secondary infection, gas gangrene (Clostridium)

Cardiovascular:

Pulmonary:

Renal/metabolic:

Hematologic:

GI:

Neurologic:

Frostbite-specific:

Board pearl: Cold-induced coagulopathy is not corrected by FFP/platelets at low temperatures — the treatment is rewarming. Don't chase numbers; chase temperature.

When to Escalate Care — ICU, Consult, and Inpatient Triage

— Core temp <32°C (moderate or severe)

— Hemodynamic instability, arrhythmia, intubation

— Acidosis, hyperkalemia, rhabdomyolysis

— Comorbid sepsis, MI, stroke as precipitants

— Severe frostbite (grade 3–4), thrombolysis administered, ongoing limb-threat

— Pediatric submersion or avalanche victims with ROSC

— Moderate hypothermia rewarmed without complications, stable mental status, controlled comorbidities

— Grade 2 frostbite with significant blistering or analgesia needs

— Mild hypothermia (>32°C) fully rewarmed with normal labs, no significant frostbite, safe disposition (warm shelter, no recurrence risk)

— Superficial frostnip with full reversal and reliable follow-up

— Cardiothoracic surgery / ECMO team: severe hypothermia with arrest or refractory instability; HOPE score guides triage

— Burn or plastic surgery: deep frostbite — they manage debridement, demarcation, and delayed amputation; frostbite is often managed in burn centers

— Vascular/interventional radiology: for IA tPA or angiography in deep frostbite

— Endocrinology: suspected myxedema or adrenal crisis

— Social work: housing instability, neglect, abuse, SUD — central to disposition planning

— Center lacks ECMO/CPB → transfer before arrest if possible; once arrested, balance transport risk vs continued CPR

— Center lacks burn/frostbite expertise → transfer within 24 hours for thrombolysis consideration

Admit to ICU:

Floor admission:

Discharge from ED considered:

Consultations:

Transfer criteria:

CCS pearl: "Consult cardiothoracic surgery, transfer to ECMO-capable facility, admit to ICU" is a high-yield CCS order set for HT III/IV; failing to escalate is graded down. Also order social work consult for any indoor urban hypothermia case.

Board pearl: Don't delay transfer for "stabilization" in severe hypothermia — definitive stabilization is ECMO at the receiving center.

Key Differentials — Same-Category (Environmental/Exposure) Causes

— Stroke: focal deficits, but hypothermia causes global slowing — image once temp >32°C if AMS persists

— Drug intoxication / overdose: ethanol, opioids, benzodiazepines, antipsychotics often coexist; tox screen and naloxone trial appropriate; don't attribute AMS solely to intoxication without checking core temp

— Trench foot / immersion foot: non-freezing cold injury from prolonged wet exposure at temps 0–15°C; mottled, painful, edematous feet; no ice crystal formation, distinguishes from frostbite. Treatment: gentle rewarming, drying, elevation, NSAIDs; tissue loss less common

— Chilblains (pernio): erythematous, pruritic, painful papules on cold-exposed skin, often hands/toes; non-freezing, immune-mediated; resolves with rewarming and avoidance; nifedipine for recurrent cases

— Cold urticaria: hives after cold exposure; allergic phenomenon; H1 antihistamines

— Raynaud phenomenon: episodic vasospasm with classic triphasic color change (white→blue→red); not freezing injury but cold-triggered

Heat-related illness mimics in reverse — patients with hypothermia mistaken for stroke or intoxication:

Other environmental injuries:

Drowning / submersion injury: often coexists with hypothermia; ARDS focus + cold injury

Avalanche burial: combined hypothermia + asphyxia + trauma; outcome depends on airway patency and burial duration

Key distinction: Trench foot vs frostbite: trench foot occurs above freezing (wet, prolonged) — skin is macerated, white, mottled but never frozen. Frostbite requires actual tissue freezing — skin is hard, waxy, anesthetic. Both can coexist in same patient.

Board pearl: A homeless patient with chronically wet socks in 5°C weather likely has trench foot, not frostbite — pivotal because management diverges (no rapid water bath rewarming for trench foot; just gentle drying and warming).

Step 3 management: Always check core temp in any "altered" winter ED patient before committing to a tox or stroke pathway — anchoring is the most common error.

Key Differentials — Other-Category Causes (Hypothermia Without Cold Exposure)

— Myxedema coma: hypothermia + bradycardia + AMS + hyponatremia + hypoventilation; check TSH/free T4; treat empirically with IV levothyroxine + hydrocortisone (give cortisol first to avoid adrenal crisis)

— Adrenal insufficiency / Addisonian crisis: hypotension, hyponatremia, hyperkalemia, hypoglycemia; cortisol stim test; hydrocortisone 100 mg IV

— Hypopituitarism / panhypopituitarism: combined endocrine failure

— Severe hypoglycemia: itself causes hypothermia; check fingerstick reflexively

— Wernicke encephalopathy: thermoregulatory dysfunction; thiamine 500 mg IV TID for 3 days

— Older adults, immunocompromised present with temp <36°C rather than fever

— Mortality is higher in hypothermic sepsis than febrile sepsis

— Full sepsis workup; broad antibiotics; fluids; lactate-guided resuscitation

— Stroke (especially hypothalamic), traumatic brain injury, spinal cord injury (loss of vasoconstriction below lesion), Wernicke's, anorexia nervosa

— Posterior hypothalamic lesions cause poikilothermia

— Extensive burns, TEN/SJS, erythroderma lose ability to vasoconstrict and retain heat — present hypothermic

— Massive transfusion if cold products not warmed

— Ethanol (most common), opioids, benzodiazepines, phenothiazines, antipsychotics, barbiturates, clonidine, beta-blockers, oral hypoglycemics

— Severe hypoglycemia, uremia, hepatic failure, lactic acidosis

Endocrine:

Sepsis (septic hypothermia):

CNS pathology:

Burns and dermatologic:

Drugs/toxins:

Metabolic:

Key distinction: Myxedema coma vs primary environmental hypothermia: myxedema has dry coarse skin, non-pitting edema, delayed reflexes, history of thyroid disease/thyroidectomy/I-131, often without significant cold exposure. Empirically treat both — TSH takes time.

Board pearl: Any hypothermic patient without cold exposure history needs TSH, cortisol, glucose, cultures, ammonia — the cold is the symptom of a deeper diagnosis.

Secondary Prevention, Discharge Medications, and Long-Term Plan

— Core temp normalized and stable >24 hr if hospitalized

— Underlying precipitant addressed (sepsis treated, endocrine started, social factors mitigated)

— Safe disposition: heated housing, shelter placement, family support, NOT back to street in winter

— Frostbite: pain controlled, no progression, plan for serial outpatient exams

— Ibuprofen 400 mg q12h × 4–6 weeks for moderate–severe frostbite (anti-thromboxane, until lesions resolve)

— Topical aloe vera BID until healed

— Analgesics: gabapentin or amitriptyline for chronic neuropathic pain from frostbite

— Tetanus update if not current

— Smoking cessation pharmacotherapy (varenicline, nicotine replacement) — smoking dramatically worsens frostbite outcomes and recurrence

— Resume/optimize meds for hypothyroidism, adrenal insufficiency, diabetes, PAD

— Address SUD: naltrexone/acamprosate for AUD; buprenorphine for OUD where appropriate

— Housing-first program enrollment, LIHEAP for heating assistance, Meals on Wheels for isolated elderly

— Outreach worker visit for repeat-offender homeless patients

— Cold-weather protective gear distribution (donated coats, sleeping bags) at discharge

— Avoid refreezing — protect previously injured tissue; chronic cold hypersensitivity is common

— Layered, moisture-wicking clothing; mittens > gloves; chemical hand/toe warmers

— Hydration, nutrition, avoidance of ethanol/tobacco in cold environments

— Recognize early warning signs: numbness, white waxy skin → seek warmth immediately

Discharge prerequisites:

Medications at discharge:

Behavioral/social:

Counseling for frostbite recurrence prevention:

Step 3 management: Discharging a hypothermic homeless patient back to the street without social work involvement and shelter referral is a sentinel safety event — document outreach attempts and capacity decisions thoroughly.

Board pearl: Frostbite survivors carry lifelong cold hypersensitivity, hyperhidrosis, and chronic pain in affected digits — counsel early and connect to chronic pain services.

Follow-Up, Monitoring, and Rehab/Counseling

— 48–72 hr: Tc-99m bone scan if grade 3–4 to map perfusion; outpatient burn/plastic clinic visit

— 1 week: blister assessment, debridement of clear blisters if not already done, infection check

— 2–4 weeks: serial exams; demarcation begins

— 6–12 weeks: surgical demarcation clearer; consider amputation if non-viable tissue declared

— 3–6 months: rehab, prosthetic fitting, occupational therapy for hand frostbite

— Long-term: monitor for chronic cold sensitivity, Raynaud-like symptoms, neuropathic pain

— PCP visit within 1–2 weeks; confirm endocrine workup follow-up (TSH recheck if levothyroxine started)

— Cardiology follow-up if cardiac complications during admission

— Address comorbid conditions identified during workup

— Occupational therapy for finger/hand frostbite — fine motor function, splinting, scar management

— Physical therapy for foot frostbite — gait retraining, prosthetic adaptation if amputation

— Psychological support — PTSD common after avalanche, prolonged exposure, near-death; consider therapy

— Chronic pain management referral for post-frostbite neuropathy

— Smoking cessation (single most important modifiable factor for recurrence/tissue survival)

— Alcohol counseling — pivotal for urban hypothermia recurrence

— Diabetes optimization (vascular protection)

— Vocational counseling if amputation affects occupation

— Pain scores, range of motion, sensory testing

— Wound infection signs

— TSH at 6–8 weeks if thyroid replacement initiated

— Mental health screening (PHQ-9, PCL-5) at follow-up

Frostbite follow-up cadence:

Hypothermia post-discharge:

Rehabilitation:

Counseling:

Monitoring parameters:

CCS pearl: On the CCS exam, after stabilizing the hypothermic patient, advance the clock to schedule 2-week PCP follow-up, smoking cessation counseling, social work referral, and burn clinic appointment — disposition planning earns credit.

Board pearl: Most frostbite outcomes are decided in the first 24 hours (rewarming + thrombolysis window), but recovery and rehab extend 6–12 months.

Ethical, Legal, and Patient Safety Considerations

— tPA carries bleeding risk; informed consent must include benefits (limb salvage) vs risks (ICH, GI bleed, death)

— Patient often in extreme pain and on opioids — assess capacity carefully; involve surrogate when indicated

— Refusal of tPA documented with clear explanation of likely amputation outcome

— Standard "death" criteria do not apply during hypothermia — prolonged CPR (hours) is appropriate

— Termination criteria (per ERC): K+ >12, asphyxial mechanism with airway packed, frozen chest wall preventing compressions, lethal injury

— Document the rationale; involve family early

— ECMO triage based on HOPE score, resource availability — utilitarian ethics in mass-casualty avalanche events

— Child neglect: pediatric hypothermia/frostbite from inadequate clothing/supervision triggers Child Protective Services report in all states

— Elder abuse/neglect: similar mandatory reporting in most states for vulnerable adults found in dangerous cold conditions

— Document findings, photograph injuries, preserve clothing as evidence if applicable

— Intoxicated or hypothermic patients lack capacity to refuse care or leave AMA

— Document mental status, capacity assessment, and rewarming before honoring refusal

— Legal hold may be appropriate for severe hypothermia + refusal

— Discharging to shelter or street in winter requires warm clothing, food, shelter bed confirmed

— Communicate directly with shelter staff or outreach team — handoff bag with discharge summary

— Avoid weekend/holiday discharges without secured follow-up

— Sentinel events: missed core temperature, premature death pronouncement, premature CPR termination, rough handling triggering VF, lactated Ringer's in severe hypothermia

— System-level: ensure low-reading thermometers, warm-fluid warmers, Bair Huggers available in all EDs

Informed consent for thrombolysis in frostbite:

Resuscitation futility decisions in severe hypothermia:

Mandatory reporting:

Capacity and AMA discharge:

Transition-of-care safety:

Patient safety in ED:

Step 3 management: Always confirm capacity before honoring refusal; cold + ethanol + hypoglycemia = no capacity. Refusal can be revisited after rewarming and sobriety.

Board pearl: "No one is dead until warm and dead" — premature termination of resuscitation in severe hypothermia is a legally and ethically actionable error.

High-Yield Associations and Rapid-Fire Clinical Facts

Core temp ranges: mild 32–35°C, moderate 28–32°C, severe <28°C, profound <24°C

Osborn (J) wave: positive J-point deflection, classic at <32°C, also seen in hypercalcemia, brain injury, Brugada

Paradoxical undressing + terminal burrowing = severe hypothermia, not crime

Afterdrop = continued temperature fall after rewarming starts; minimized with trunk-only active rewarming

K+ >12 mmol/L = futility marker in cold cardiac arrest

HOPE score triages severe hypothermia for ECMO

Frostbite rewarming: 37–39°C circulating water × 15–30 min until pliable

NSAIDs (ibuprofen) + aloe vera + tetanus + opioids = frostbite quartet

tPA window: <24 hr from rewarming for grade 3–4 frostbite

Iloprost: alternative to tPA, lower bleeding risk

Bone scan at 48 hr: best predictor of frostbite viability; "amputate in July"

Refreezing is worse than delayed thaw — don't rewarm if refreeze possible

Hemorrhagic blisters = leave intact; clear blisters = aspirate/debride

Trench foot = non-freezing, wet, above 0°C; never rewarm in warm water bath

Chilblains (pernio) = pruritic erythematous papules; treat with nifedipine if recurrent

Submersion <5°C in pediatrics = aggressive resuscitation even with prolonged downtime

Mammalian dive reflex = bradycardia + peripheral vasoconstriction + blood shunting to brain/heart on cold facial immersion

Cold AF: do NOT cardiovert or anticoagulate; resolves with rewarming

Avoid lactated Ringer's in severe hypothermia (impaired lactate clearance)

Empiric T4 + hydrocortisone for suspected myxedema — cortisol first

Brown fat = primary infant thermogenesis (non-shivering)

ABG: interpret uncorrected values

Vasopressors below 30°C: typically withheld

One defibrillation attempt if VF and <30°C, then rewarm first

Board pearl: If you remember one number: K+ >12 = stop; pH < 6.5 = stop; otherwise rewarm aggressively before declaring death. If you remember one phrase: "Warm and dead."

Key distinction: Active external vs active internal rewarming — external is forced-air/heating pads (moderate); internal is lavage/ECMO (severe). Choose based on temp and stability.

Board Question Stem Patterns

— "Found unconscious in snowbank, rectal temp 24°C, asystole. After one cycle of CPR and defibrillation attempt, what is the next best step?"

— Answer: Continue CPR and transfer for ECMO/CPB rewarming; do not declare death; vasoactive drugs held; further defibrillation deferred until >30°C

— "Climber rescued after 48 hrs, fingers waxy and hard. After rewarming at base camp, hemorrhagic blisters form. What is the next step?"

— Answer: Tc-99m bone scan and consider IV tPA if within 24 hr of rewarming; ibuprofen, aloe, tetanus; leave hemorrhagic blisters intact; do NOT amputate early

— "82 yo found at home, temp 32°C, HR 42, lethargic, hyponatremic, non-pitting edema, scar on neck. Workup?"

— Answer: TSH, free T4, cortisol; empirically give hydrocortisone first, then levothyroxine; passive + active external rewarming

— "5 yo fell into frozen lake, submerged 25 min, asystole, temp 22°C. What is the most appropriate management?"

— Answer: Continue CPR; transfer for ECMO; full neurologic recovery possible despite prolonged downtime

— Drunk patient with temp 33°C wants to leave AMA. Best action?

— Answer: Patient lacks capacity; rewarm + sober first, reassess capacity, document; safety hold if needed

— Cold-exposed patient with bradycardia + positive J-point deflection. Diagnosis and next step?

— Answer: Hypothermia; rewarm; cardiac monitoring; gentle handling

— Homeless patient with wet, macerated, mottled feet after 3 days in 5°C rain — trench foot, NOT frostbite; gentle drying, elevation, NSAIDs, no warm water immersion

Classic stem 1 — Severe hypothermia with cardiac arrest:

Classic stem 2 — Frostbite in mountaineer:

Classic stem 3 — Elderly woman with myxedema mimic:

Classic stem 4 — Pediatric cold-water submersion:

Classic stem 5 — Refusing care, intoxicated:

Classic stem 6 — ECG with Osborn waves:

Classic stem 7 — Trench foot vs frostbite:

CCS pearl: Common CCS sequence: core temp probe → warm IV fluids → forced-air rewarmer to torso → cardiac monitor → labs (CBC, BMP, glucose, ABG, K+, lactate, TSH, cortisol, tox screen) → ECG → CXR → consult CT surgery for ECMO → ICU admit → advance clock q15min → repeat temp.

Board pearl: When in doubt on Step 3: measure core temperature, rewarm, transfer to ECMO center, consult social work — these four actions cover 80% of credit.

One-Line Recap

In hypothermia and frostbite, the core teaching is: measure core temperature with a low-reading probe, rewarm aggressively using a strategy matched to severity (passive → active external → active internal/ECMO), withhold death pronouncement until "warm and dead," and salvage frostbitten tissue with rapid water-bath rewarming plus ibuprofen and consideration of tPA or iloprost before any amputation.

Recap 1 — Triage by temp: Mild (32–35°C) = passive external rewarming and oral fluids; moderate (28–32°C) = active external rewarming to trunk only + warm IV fluids; severe (<28°C) or arrest = active internal rewarming with ECMO/CPB as gold standard. Use K+ >12, pH <6.5, asphyxial mechanism as futility markers, otherwise resuscitate prolonged.

Recap 2 — Frostbite essentials: Rapid rewarming in 37–39°C circulating water × 15–30 min ONLY if refreezing impossible; ibuprofen + aloe + tetanus + opioids + bone scan at 48 hr; tPA within 24 hr for grade 3–4 deep frostbite at specialized center; leave hemorrhagic blisters intact; "frostbite in January, amputate in July" — delay surgery until clear demarcation.

Recap 3 — Don't miss the mimics: Hypothermia without cold exposure means sepsis, myxedema coma, adrenal crisis, hypoglycemia, intoxication, or CNS pathology — always send TSH, cortisol, glucose, cultures, tox screen. Empirically treat suspected myxedema with hydrocortisone first, then levothyroxine.

Recap 4 — Safety & disposition: Capacity is impaired by cold + ethanol + hypoglycemia — rewarm before honoring AMA refusal; involve social work, shelter placement, LIHEAP, smoking cessation, SUD treatment before discharge; report child neglect or elder abuse when cold exposure reflects inadequate care. No one is dead until warm and dead.