Snapshot An 87-year-old homeless military veteran is found unconscious in an alleyway in the middle of January. He was wearing a shirt, a sweater, a pair of pants, and a peacoat. He is brought by ambulance to the ED, where vitals are quickly obtained; his blood pressure is 100/50 mmHg, pulse is 50/min, and SaO2 is 92% on RA. Rectal temperature of 87.6°F (30.8°C) is measured. Naloxone was administered enroute by paramedics with no recovery of mental status. The patient is intubated and mechanically ventilated with warm humidifed O2. IV normal saline is infused at room temperature. Initial EKG monitoring reveals sinus bradycardia with no J-point variations or ST-T wave changes. A second EKG is completed and reveals the findings above. The trauma bay temperature is increased to 82°F (27.8°C). The patient's clothing is quickly cut and replaced with a dry blanket Bair Hugger. No evidence of cold injury is observed. Rectal temperature decreases to 85°F (29.4°C). The patient is transferred to the intensive care unit. Introduction Hypothermia is core temperature below 95°F (35°C) mild: 90 - 95°F (32 - 35°C) moderate: 82 - 90°F (28 - 32°C) severe: < 82°F (< 28°C) Cold-associated injuries along spectrum frostnip local paresthesia without permanent tissue injury pernio inflammatory lesion especially in cold and damp environment immersion foot (nonfreezing cold injury) inflammatory lesion with potential permanent tissue injury frostbite (freezing cold injury) inflammatory lesion due to intra- and extracellular ice crystal formation requires debridement, antibiotics, tetanus vaccination rhabdomyolysis possible may cause hyperkalemia, hyperphosphatemia, hypocalcemia Etiology Pathogenesis Mechanism of hypothermia depends on location 4 mechanisms of heat loss radiation - emission of electromagnetic energy convection - transfer of heat to air or water conduction - transfer of heat to solid object evaporation - vaporization of water radiation is main mechanism of heat loss in surgical setting (i.e. OR) due to increased exposure of body surface area conduction/convection are main mechanisms of heat loss in accidental hypothermia Presentation Predisposing factors to hypothermia age (particularly very young and very old) lack of housing drug overdose alcohol ingestion trauma cold water immersion/sports Symptoms and signs based on hypothermia severity mild: tachycardia normal mental status + shivering moderate: bradycardia, tachycardia with Osborn (J) waves on EKG altered mental status - shivering severe: ventricular fibrillation/asystole, unconscious arrhythmia is the most common cause of death from hypothermia STUDIES Based on major complications of hypothermia, including coagulopathy, acidosis, arrhythmia, and FEN derangements coagulation: CBC, PT/INR/PTT acidosis: ABG, lactate arrhythmia: 12-lead EKG Osborn J-waves distortion of early repolarization in V2-V5 at beginning of ST segment can be confused for ischemic injury not sensitive, specific, or prognostic FEN: electrolytes, BUN/Cr, glucose, Ca2+, Mg2+ Radiography CXR may show evidence of aspiration pneumonia/pulmonary edema Evaluation and Management Primary and secondary survey with resuscitation if patient presents with cardiac arrest in setting of hypothermia: best initial step: rewarm body next step: ACLS algorithm based on arrhythmia (VFib / PEA however, if any pulse exists, do NOT perform CPR do NOT treat new supraventricular arrhythmia pharmacologically rewarming strategy is based on hypothermia severity, but goal is at least 0.9°F/hour mild: passive external rewarming elevate room temperature to 82°F (27.8°C) remove wet clothes and replace with dry blanket moderate: active external and internal rewarming active external: warm blanket, warm bath warm trunkbefore extremities to lower risk of "afterdrop" event warming of extremities -> vasodilation -> cool blood moves from extremities to core -> cardiac arrest active internal: warmed IV infusion and warmed, humidified oxygen severe: same as for moderate hypothermia with possible extracorporal options peritoneal and pleural irrigation with warmed fluids cardiopulmonary bypass peritoneal dialysis with warmed fluids physical exam must document cardiovascular and neurological status, and evidence of cold-assciated skin injuries Frostbite-specific management immersion in 98.6-102.2°F (37 - 39°C) water for 10-30 minutes every day provide pain medications! cleaning and debridement tetanus prophylaxis NO prophylactic antibiotics