Hypothermia & Drowning
Core temp < 35°C. Mild (32–35°C): shivering. Moderate (28–32°C): loss of shivering, confusion, Osborn waves. Severe (< 28°C): VF risk, appears dead. Warm before declaring death. Active rewarming for moderate-severe.
🔍 Overview
Classification
| Severity | Temp Range | Key Features | Treatment |
|---|---|---|---|
| Mild | 32–35°C | Shivering, tachycardia, vasoconstriction, altered judgment | Passive external rewarming (blankets, warm room). Remove wet clothing. |
| Moderate | 28–32°C | Shivering stops, confusion→stupor, bradycardia, Osborn (J) waves on ECG, atrial fibrillation | Active external rewarming (Bair Hugger, warm packs to axillae/groin). Warm IV fluids 40–42°C. |
| Severe | < 28°C | Coma, areflexia, VF risk, fixed dilated pupils, appears dead | Active core rewarming (warm humidified O₂, peritoneal/pleural lavage, ECMO). Withhold meds until ≥ 30°C. |
| Profound | < 24°C | Asystole, no vital signs. May still be salvageable with rewarming. | ECMO/cardiopulmonary bypass (gold standard). Prolonged CPR. Do NOT declare death. |
"No one is dead until they are warm and dead." Do NOT declare death until core temp ≥ 32°C and rewarming efforts have failed. Hypothermia is neuroprotective -full recovery has occurred after prolonged cold-water submersion.
🚨 Management
Rewarming Strategies
| Method | Indication | Rate of Rewarming |
|---|---|---|
| Passive external (blankets, warm room, remove wet clothes) | Mild hypothermia (32–35°C). Patient can generate heat via shivering. | 0.5–2°C/hr |
| Active external (Bair Hugger, warm packs to axillae/groin) | Moderate hypothermia (28–32°C). Shivering lost, patient cannot self-rewarm. | 1–2°C/hr |
| Warm IV fluids (NS/LR at 40–42°C) | Moderate–severe. Adjunct to other rewarming methods. | Modest contribution (~0.5°C/hr alone) |
| Warm humidified O₂ (42–46°C via ETT or NRB) | Moderate–severe. Active core rewarming adjunct. | 1–1.5°C/hr |
| Peritoneal/pleural lavage (42°C warm saline) | Severe (< 28°C) when ECMO unavailable. More effective than bladder lavage. | 2–4°C/hr |
| ECMO / cardiopulmonary bypass | Severe hypothermic cardiac arrest. Gold standard. | 5–10°C/hr |
Cardiac Arrest in Hypothermia
- ECMO/CPB -gold standard rewarming for VF arrest in hypothermia. Rewarms at 5–10°C/hr.
- Continue CPR -may need prolonged resuscitation
- Defibrillation: May attempt up to 3 shocks if temp < 30°C. If unsuccessful, defer further shocks until core temp ≥ 30°C.
- Medications: Withhold vasopressors and antiarrhythmics until core temp ≥ 30°C (drugs don't work and accumulate in cold circulation)
Drowning Management
- Rescue breathing is the priority -drowning is a hypoxic event. Begin ventilation as soon as possible, even in the water if safe.
- Cervical spine precautions -maintain inline stabilization if diving injury, trauma, or mechanism suggests c-spine injury. However, routine c-spine immobilization in all drowning victims is NOT supported.
- Warm IV fluids -most drowning victims are hypothermic. Start warm NS/LR (40–42°C). Treat concomitant hypothermia aggressively per rewarming protocols above.
- Pulmonary edema -watch for delayed pulmonary edema 24–48 hours post-submersion. Aspirated water disrupts surfactant and damages alveolar epithelium. CXR may be initially normal but deteriorate.
- Freshwater vs saltwater -freshwater is hypotonic (washes out surfactant, absorbed into circulation). Saltwater is hypertonic (pulls fluid into alveoli). Clinical management is the same for both.
- Prognostication:
- Submersion time -strongest predictor. > 25 min submersion in warm water = very poor prognosis.
- Water temperature -cold water (< 6°C) is neuroprotective. Full neurologic recovery reported after > 60 min submersion in ice water (especially children).
- Age -children have better outcomes than adults due to higher surface-area-to-body-mass ratio → faster cooling → more neuroprotection.
- CPR duration and initial rhythm -faster ROSC = better outcome. VF is better than asystole.
Cold-water drowning in children: Aggressive rewarming and prolonged resuscitation are warranted. The combination of rapid cooling + diving reflex can provide profound neuroprotection. Do not stop early.
🧪 Workup
- Core temperature -rectal or esophageal probe (NOT oral/tympanic -inaccurate in hypothermia)
- ECG -Osborn (J) waves, prolonged intervals, atrial fibrillation, VF
- ABG -pH interpretation complex (use temperature-corrected values)
- BMP -hyperkalemia (cell lysis), hypoglycemia
- CBC, coags (hypothermia causes coagulopathy)
- Lactate
- TSH, cortisol -rule out myxedema/adrenal crisis as cause
💊 Medications
| Intervention | Details | Notes |
|---|---|---|
| Warm IV NS/LR (40–42°C) | 250–500 mL boluses | Use fluid warmer. Contributes modestly to rewarming. |
| Warm humidified O₂ | 42–46°C via ETT or NRB | Active core rewarming adjunct |
| Warm bladder lavage | 42°C NS via 3-way Foley | Moderate core rewarming |
| Warm peritoneal lavage | 42°C NS via peritoneal catheter | More effective than bladder lavage |
| ECMO | Venoarterial (VA-ECMO) | Gold standard for severe hypothermic cardiac arrest. Rewarms 5–10°C/hr. |
Withhold IV medications until core temp ≥ 30°C. Drugs are ineffective in cold circulation, don't metabolize, and accumulate → risk of toxicity when patient rewarms.
📋 On Rounds
Pimp Questions
What are Osborn (J) waves?
Positive deflection at the J point (junction of QRS and ST segment) on ECG, pathognomonic for hypothermia. Appear at core temp < 32°C, increase in amplitude as temperature drops. Also called "J waves" or "hypothermic hump." Resolve with rewarming. Not an indication for anti-arrhythmic therapy.
Why is K⁺ > 12 mEq/L considered non-survivable in hypothermia?
Severe hyperkalemia (> 12) in hypothermia indicates massive cell lysis and tissue death -the cells have been irreversibly damaged by ice crystal formation. This level of intracellular potassium release means the patient likely has extensive organ damage incompatible with survival, even with successful rewarming. It is one of the few criteria used to guide termination of resuscitation in hypothermic arrest.
📋 Case 1, Moderate Hypothermia (Found Down)
Patient: 78M found on his kitchen floor by a neighbor. Last seen well 18 hours ago. Confused, minimally responsive. Temp: 30.1°C (rectal). HR 38 (bradycardia). BP 88/54. RR 8.
ECG: Sinus bradycardia with Osborn (J) waves at the J-point. QTc prolonged. No VF.
Labs: K⁺ 5.8, glucose 48 (hypoglycemic), lactate 3.2, TSH pending, cortisol pending.
Management:
- Remove all wet/cold clothing. Dry skin. Wrap in warm blankets.
- Active external rewarming: Bair Hugger forced-air warming blanket. Warm packs to axillae and groin (high-flow areas). Target: rewarm the trunk first.
- Warm IV fluids: NS at 40–42°C via fluid warmer, 250–500 mL bolus. Correct hypoglycemia with D50W.
- Do NOT treat bradycardia or AF with medications, the arrhythmia is from hypothermia and will resolve with rewarming.
- Check TSH and cortisol, hypothyroidism and adrenal insufficiency are precipitating causes of hypothermia in the elderly.
- K⁺ 5.8: Monitor closely. Expected to improve with rewarming. K⁺ >12 = non-survivable (massive cell lysis); K⁺ 5.8 is compatible with survival.
- Serial core temps q1h (esophageal or rectal probe) and continuous telemetry during rewarming.
Teaching point: In elderly patients found down, always measure core temperature. Oral/tympanic temps are unreliable, use rectal or esophageal probe. Check TSH and cortisol; hypothyroidism is a classic precipitant of hypothermia in the elderly.
📋 Case 2, Severe Hypothermia with VF Arrest
Patient: 32M found unresponsive in a snowbank by ski patrol. No pulse, no respirations. Estimated outdoor exposure 2+ hours. Initial core temp: 24°C.
In the field: CPR initiated immediately. AED delivered 1 shock, rhythm remained VF. Patient transported to ED with ongoing CPR.
In the ED:
- Confirm core temperature with esophageal probe: 24°C, profound hypothermia
- Continue CPR, do not stop. Hypothermia is neuroprotective; viable patients have been resuscitated after >6 hours of CPR.
- Attempt defibrillation × 3 total (have already done 1 in field). If unsuccessful at <30°C, defer further shocks until core temp ≥30°C.
- Withhold epinephrine and amiodarone until core temp ≥30°C, drugs accumulate and are ineffective in cold circulation.
- ACTIVATE ECMO TEAM STAT, VA-ECMO is the gold standard for hypothermic cardiac arrest. Can rewarm at 5–10°C/hr.
- K⁺: 7.2, compatible with survival. Proceed with rewarming.
- ECMO initiated. Core temp rises over 90 minutes to 32°C → spontaneous ROSC, VF terminates. Patient extubated day 3. Full neurologic recovery.
Teaching point: K⁺ >12 mEq/L = non-survivable (massive cell lysis). This patient's K⁺ 7.2 meant the cells were still viable, aggressive ECMO rewarming was warranted. "No one is dead until warm and dead."
📋 Case 3, Cold-Water Drowning in a Child
Patient: 7F falls through ice on a frozen pond. Submerged approximately 45 minutes before rescue. Core temp on EMS arrival: 22°C. No pulse. Pupils fixed and dilated. Cyanotic.
EMS: CPR initiated. Bystanders attempted rescue within 5 minutes of submersion.
ED Management:
- Core temp 22°C, do NOT declare death. "No one is dead until warm and dead."
- Fixed dilated pupils, absent reflexes: all expected findings at this temperature. Do not use these as markers of irreversibility in hypothermia.
- ECMO activation, VA-ECMO for hypothermic cardiac arrest. Children have better outcomes than adults (faster cooling via diving reflex + higher surface-area-to-mass ratio).
- Warm via ECMO, core temp rises to 36°C over 2 hours. ROSC at core temp 30°C (sinus bradycardia → normal sinus rhythm with rewarming).
- Post-resuscitation care: Targeted temperature management at 33–36°C × 24h. ICU monitoring. Neurologic exam serially.
- Day 5: Extubated. Neurologically intact. Discharged day 10.
Teaching point: The mammalian diving reflex + rapid hypothermic cooling in ice water provides profound neuroprotection in children. The protective combination: apnea + bradycardia + peripheral vasoconstriction + near-freezing temperatures drops oxygen consumption to near zero. Full neurologic survival after prolonged submersion is well-documented in pediatric cold-water drowning, never stop early.
⚡ Summary
Stage It by Core Temperature
Mild 32 to 35°C: still shivering, tachycardic. Moderate 28 to 32°C: shivering stops, confusion to stupor, bradycardia, Osborn (J) waves. Severe below 28°C: coma, areflexia, fixed dilated pupils, high VF risk. Profound below 24°C: asystole. Loss of shivering is the key transition, because the patient can no longer generate their own heat and passive rewarming stops working.
Match the Rewarming to the Stage
Mild → passive external (dry clothes, blankets, warm room, 0.5 to 2°C/h). Moderate → active external (forced-air warmer, packs to axillae and groin, 1 to 2°C/h). Severe → active core (warm humidified oxygen, warm IV fluids, peritoneal or pleural lavage at 2 to 4°C/h). Hypothermic arrest → ECMO or bypass, which is the gold standard at 5 to 10°C/h.
Nobody Is Dead Until Warm and Dead
Do not declare death until the core temperature is at least 32°C and rewarming has failed. Hypothermia is neuroprotective, and intact neurological recovery has followed prolonged cold-water submersion, so the cold patient who looks dead is resuscitated first and pronounced later.
Handle Them Gently
The severely hypothermic myocardium is irritable and will fibrillate from rough handling, so move the patient carefully and avoid unnecessary jostling and non-essential line placement.
Drugs and Shocks Behave Differently in the Cold
Withhold IV medications until the core temperature reaches 30°C: cold circulation makes them ineffective and they are not metabolized, so they accumulate and become toxic on rewarming. Limit defibrillation to a maximum of 3 attempts below 30°C, then rewarm before trying again.
Rewarming Has Its Own Complications
Afterdrop: cold peripheral blood returning centrally drops the core temperature further, which is why the trunk is rewarmed before the limbs. Rewarming collapse: peripheral vasodilation unmasks a profound volume deficit, so anticipate hypotension and give warmed fluids. Also watch potassium and glucose, which shift as the patient warms.
Drowning Is a Hypoxia Problem
Ventilation comes first, not compressions, because the arrest is asphyxial. Fresh versus salt water does not change management. Anyone symptomatic needs 4 to 8 h of observation, since pulmonary injury can declare itself late; the truly asymptomatic patient with a normal exam and saturation can go home.
Push Longer in Cold-Water Drowning, Especially in Children
Rapid cooling plus the diving reflex can be profoundly neuroprotective, so aggressive rewarming and prolonged resuscitation are warranted and the usual stopping rules do not apply. Do not stop early.
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