Even though we're going into the summer, here's a great review of accidental hypothermia by Dr. Ledrick.
Case
A 47-year-old man was walking home intoxicated last night when he became unconscious falling into a snow drift. He was found this morning and brought to the ED by EMS. He is somnolent, without signs of overt trauma, and with a core temperature of 30°C. Exam of the extremities shows pallor to the distal circulation. He is responsive to voice and able to protect his airway but is somewhat disoriented. He is not shivering. His vital signs are: HR 42 with atrial fibrillation on the monitor, RR of 6, SpO2 in the low 90s%, BP 90/60mmHg.
What are some considerations to be conscious of in the first 10 minutes of evaluation?
How should the arrhythmia be treated?
What potential issues may result during rewarming?
What is an appropriate disposition for this patient?
Presentation and Diagnosis
Each degree of hypothermia has the symptoms above it, unless otherwise specificed
Cold stressed - not hypothermic - Estimated core temperature 35 to 37°C (95 to 98.6°F) - Normal mental status with shivering - Functioning normally - Able to care for self
Mild hypothermia (32°C to 35°C) - Tachypnea, tachycardia, initial hyperventilation - Ataxia, dysarthria, impaired judgment - Shivering - "Cold diuresis"
Moderate hypothermia (28°C to 32°C) - Atrial fibrillation, junctional bradycardia, and other arrhythmias can occur. - Pupillary light reflex is depressed through slowing of both constriction and dilation, dilated pupils are seen below a core temperature of about 29°C. - Shivering stops
Severe hypothermia (less than 28°C) - Pulmonary edema - Oliguria - Areflexia, coma - Hypotension, bradycardia, ventricular arrhythmias (including ventricular fibrillation), and asystole
At patient presentation, beware of vital signs inconsistent with the degree of hypothermia - A relative tachycardia inconsistent with the core temperature suggests hypoglycemia, hypovolemia, or an overdose. - Relative hyperventilation implies an underlying organic acidosis (eg, diabetic ketoacidosis, aspirin overdose), since CO2 production should be decreased in moderate or severe hypothermia. - Moderate and severely hypothermic patients should be bradycardic and hypoventilating - Pulse ox placed on finger is slowed by hypothermia; if placed on the ears or forehead, it appears to be less influenced by decreased body temperature
Temperature measurement - Use of a low-reading thermometer to determine core temperature - Many standard thermometers read only to a minimum of 34°C (93°F) and are therefore unsuitable. - Esophageal temperature is the most accurate method to track the progress of rewarming - Bladder temperatures are commonly used and are adequate in mild to moderate hypothermia - Changes in rectal and bladder temperatures significantly lag behind core temperature changes during rewarming
Other considerations: - Inhibition of the coagulation cascade enzymes leads to bleeding diathesis but coag labs may be reported as normal; administration of clotting factors is ineffective - Osborn waves may be present on ECG; the height of the wave corresponds to the degree of hypothermia (Vassallo 1999) - Hematocrit increases 2 percent for each 1°C drop in temperature; a low/normal hematocrit is abnormal in severe hypothermia - Hyperglycemia that persists during rewarming suggests pancreatitis or diabetic ketoacidosis; insulin is ineffective below 30°C
Treatment
Remove wet clothing and cover with warm clothes or blankets
Patients with moderate or severe hypothermia frequently become disproportionately hypotensive during rewarming from severe dehydration and fluid shifts - Large infusions (with warmed crystalloid 40-42°C) may be necessary; room-temperature fluids can worsen hypothermia - Low-dose dopamine (2-5mcg/min) can be used for refractory cases; other vasopressors are acceptable, but studies to support their use have not been performed
***CONTROVERSIAL***: Especially in chronic hypothermia with dehydration, rewarming of the trunk should be undertaken BEFORE the extremities. These actions are performed in order to minimize core temperature afterdrop with associated hypotension and acidemia due to arterial vasodilation (Webb 1986, Roggla 2002)
Core temperature afterdrop is a particular risk of active external rewarming - Occurs when the extremities and trunk are warmed simultaneously - Cold, acidemic blood that has pooled in the vasoconstricted extremities of the hypothermic patient returns to the core circulation, causing a drop in temperature and pH
ACTIVE EXTERNAL REWARMING (AER) - applying heat directly to the body externally - warm blankets - heating pads - radiant heat - warm baths - forced warm air
ACTIVE CORE REWARMING (ACR) - applying heat directly to the core internally
Stepwise Approach - The combination of ACR, using heated IV infusions and warmed humidified oxygen, and AER provides an effective initial strategy for most spontaneously perfusing, severely hypothermic patients - Peritoneal irrigation can be performed by infusing 10 to 20 mL/kg of isotonic saline warmed to approximately 42°C - Pleural irrigation can be accomplished by placing two thoracostomy tubes large enough to allow unimpeded rapid infusion and drainage of saline (36 to 40 French) in one or both hemithoraces - Endovascular warming devices are an effective and less invasive alternative to extracorporeal blood rewarming - Femoral catheter that circulates temperature-controlled water inside a closed catheter tip in the femoral vein (eg. Quattro catheter) - A minimally invasive method of rewarming in a case of severe accidental hypothermia, using an esophageal heat transfer device, has been described. - Extracorporeal blood rewarming - Cardiopulmonary bypass and venoarterial ECMO reserved for: hemodynamic instability, failure to rewarm, completely frozen extremities, severe rhabdomyolysis with hyperkalemia - Other options (these will likely require heparinization, which may not be possible in certain cases such as trauma) - Venovenous rewarming circuit (without ECMO) - Hemodialysis achieves similar rewarming rates - Continuous arteriovenous rewarming (CAVR) requires a systolic blood pressure of 60 mmHg - Cardiopulmonary Bypass (CPB)
CPR: start immediately and provide continuously if possible; can be delayed up to 10 minutes while rescuers move the patient to a safer location - Contraindications: verified DNR status, obviously lethal injuries, a frozen chest wall that is not compressible, and the presence of any signs of life - ***CONTROVERSIAL***: Chest compressions should not be performed in patients who manifest an organized rhythm on monitor; such rhythms may reflect successful perfusion that could be disrupted by chest compressions. Hypothermic patients may exhibit cardiac irritability and rough handling runs the risk of precipitating ventricular arrhythmias, including V-Fib. (However, this risk may be over-stated). - PEA is likely transient
Ventricular arrhythmias and asystole may be refractory to conventional therapy until the patient has been rewarmed. Focus aggressively on rewarming the patient. Defibrillation may be ineffective below 30°C. Evidence to support drug therapy prior to successful rewarming is limited.
Bradycardia may be physiologic in severe hypothermia. Cardiac pacing generally is not required unless the bradycardia persists despite rewarming to 32 to 35°C (90 to 95°F).
Atrial fibrillation and flutter do not cause a rapid ventricular response and often resolve spontaneously with rewarming
Disposition
Most patients with moderate or severe hypothermia will need to be admitted for continued monitoring.
Evidence is limited and conflicting - Largest study, performed over 25 years ago, factors associated with death included: prehospital cardiac arrest, low or absent blood pressure on presentation, elevated BUN, endotracheal intubation - Japanese registry study showed these factors were associated with increased in-hospital mortality from accidental hypothermia: age ≥75 years, frailty, hemodynamic instability, and hyperkalemia
Outcome did not correlate with core temperature at presentation - Poor prognosis if associated with asphyxia by drowning or avalanche - Witnessed cardiac arrest is a strong predictor of a more favorable neurological outcome in patients with hypothermia but not asphyxia - Observationally, almost all healthy patients, who develop accidental hypothermia and are hemodynamically stable, survive neurologically intact - Among patients who sustain cardiac arrest from accidental hypothermia, the rate of neurologically intact survival is estimated to be approximately 50% when they are treated with extracorporeal circulation, and less than 37% with other treatment methods
References and Other Resources:
Singh A, Stead T G, Mangal R, et al. (July 06, 2019) Severe Hypothermia in the Sunshine State. Cureus 11(7): e5088. doi:10.7759/cureus.5088e
Okada Y, Matsuyama T, Morita S et al Prognostic factors for patients with accidental hypothermia: A multi‐institutional retrospective cohort study. Am. J. Emerg. Med. 2019; 37: 565–70.
Webb P. Afterdrop of body temperature during rewarming: an alternative explanation. J Appl Physiol (1985). 1986 Feb;60(2):385-90.
Vassallo SU, Delaney KA, Hoffman RS, Slater W, Goldfrank LR. A Prospective Evaluation of the Electrocardiographic Manifestations of Hypothermia. Academic Emergency Medicine. 1999;6(11):1121-1126. doi:10.1111/j.1553-2712.1999.tb00114.x.
Post edited by: Shyam Murali, MD