Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 37-03: Accidental Systemic Hypothermia + Key Features Download Section PDF Listen +++ +++ Essentials of Diagnosis ++ Systemic hypothermia is a core body temperature (CBT) below 35°C Accurate CBT measurement must be obtained using a low-reading core temperature probe than measures as low as 25°C The CBT must be over 32°C before terminating resuscitation efforts Extracorporeal membrane oxygenation (ECMO) or cardiopulmonary bypass may be considered in hypothermic patients with hemodynamic instability or cardiac arrest +++ General Considerations ++ Risk factors Diabetes mellitus and other endocrine dysfunctions (hypothyroidism, adrenal insufficiency, hypopituitarism) Kidney or liver dysfunction Psychiatric conditions Poor nutrition Sedentary lifestyle Homelessness, inadequately heated housing, inadequate or wet clothing Occupational or recreational exposure Prior cold weather injury Pharmacologic effects Sepsis, infection Hypoglycemia Heat loss occurs more rapidly with High wind velocity ("windchill factor") Water immersion or wet clothing Direct contact with a cold surface Accidental hypothermia may occur in the hospital setting due to Prolonged postoperative hypothermia or administration of large amounts of refrigerated stored blood products (without rewarming) Rapid infusion of intravenous fluids Prolonged exposure of an undressed patient during resuscitation or surgical procedures Systemic hypothermia Depresses physiologic function, resulting in decreased respiratory drive, oxygen consumption, central or peripheral nerve conduction, gastrointestinal motility, myocardial repolarization, metabolism of drugs May decrease activity of coagulation cascade and the immune response + Clinical Findings Download Section PDF Listen +++ +++ Symptoms and Signs +++ Systemic hypothermia ++ In mild cases with core temperature between 35°C and 32°C (stage I): Shivering Impaired coordination Poor judgment Hemodynamic stability Normal level of consciousness With core temperature between 32°C and 28°C (stage II): Shivering stops Bradycardia, dilated pupils, slowed reflexes, cold diuresis, and confusion and lethargy ensue With core temperature between 28°C and 24°C (stage III) Loss of consciousness Vital signs present Below 24°C (stage IV): Vital signs lost Coma, loss of reflexes, asystole or ventricular fibrillation, which may lead the clinician to assume that patient is dead despite reversible hypothermia +++ Hypothermia of the extremities ++ Exposure of the extremities to cold produces immediate localized vasoconstriction followed by generalized vasoconstriction When the skin temperature falls to 25°C, the area becomes cyanotic At 15°C, there is a deceptively pink, well-oxygenated appearance to the skin. Tissue damage occurs at this temperature +++ Differential Diagnosis ++ Infection Other cause of altered mental status (eg, hypoglycemia, drugs, stroke) Hypothyroidism Anorexia or malnutrition (poor fat stores) Adrenal insufficiency Burns Spinal cord injury + Diagnosis Download Section PDF Listen +++ +++ Laboratory Tests ++ Must assess acid-base status; electrolytes (particularly potassium); glucose; kidney, liver, and pancreas function; and coagulation; and must exclude rhabdomyolysis +++ Diagnostic Procedures ++ ECG may reveal J wave or Osborn wave (positive deflection in the terminal portion of the QRS complex, most notable in leads II, V5, and V6) (Figure 37–1) During the rewarming process, essential testing includes ECG, chest radiograph, arterial blood gas and bedside glucose monitoring ++ Figure 37–1. Electrocardiogram shows leads II and V5 in a patient whose body temperature is 24°C. Note the bradycardia and Osborn waves. These findings become more prominent as the body temperature lowers and gradually resolve with rewarming. Osborn waves have an extra positive deflection in the terminal portion of the QRS complex and are best seen in the inferior and lateral precordial leads (most notably in leads II, V5, and V6). Graphic Jump LocationView Full Size||Download Slide (.ppt) + Treatment Download Section PDF Listen +++ +++ Therapeutic Procedures ++ Mild hypothermia (Stage I hypothermia, rectal temperature 35°C to 32°C) in healthy patients: warm bed or rapid passive rewarming with warm bath or warm packs and blankets Moderate hypothermia (Stage II hypothermia, core temperature 32°C to 28°C; and Stage III hypothermia, core temperature 28°C to 24°C) Establish cardiovascular support, acid-base balance, arterial oxygenation, and adequate intravascular volume before rewarming to minimize risk of organ infarction and "afterdrop" (recurrent hypothermia) Active external and internal rewarming Below 30°C, arrhythmias and asystole may be refractory to drug therapy until the patient has been rewarmed, therefore treatment should focus on excellent technique CPR done in conjunction with aggressive rewarming of the patient Severe hypothermia (Stage IV hypothermia, core temperature below 24°C) For severely hypothermic patients in cardiac arrest, high-quality CPR must be initiated and continued until the patient's core body temperature is at least 32°C Epinephrine or vasopressin may be given to a severely hypothermic patient in cardiac arrest International Commission for Mountain Emergency Medicine recommends extracorporeal life support as the treatment of choice for patients with high risk of hypothermic cardiac arrest +++ Active external rewarming ++ Warm bedding, heated blankets, heat packs, and immersion into a 40°C bath Easier to monitor and perform diagnostic and therapeutic procedures using heated blankets Rewarming may cause marked peripheral dilation, predisposing to ventricular fibrillation and hypovolemic shock Afterdrop can be lessened by active external rewarming of the trunk but not the extremities and by avoiding any muscle movement by the patient There is some evidence to suggest that head warming is a viable alternative to increase core body temperature if torso warming in contraindicated (eg, when performing cardiopulmonary resuscitation) +++ Active internal (core) rewarming ++ Warm humidified oxygen (43–46°C) is an easy, safe, and highly effective method Warmed intravenous saline infusions (43°C) should be used instead of lactated Ringer solution Volume resuscitation is needed to prevent shock as vasodilation occurs during rewarming Other methods include Warm solution lavage of the stomach, colon, thoracic cavity, peritoneum, or bladder Extracorporeal blood rewarming by cardiopulmonary, arteriovenous femorofemoral, or venovenous bypass Hemodialysis Endovascular warming devices are a less invasive alternative than extracorporeal methods but are not widely available in hospitals For patients with core temperature < 30°C: Active rewarming Cardiopulmonary resuscitation (CPR) One shock attempt for dysrhythmia Withholding of intravenous medications Once the core temperature reaches 30°C: Cardiac medications can be given but at longer than standard intervals because metabolism is slowed and there is a risk of toxic accumulation as circulation is restored Defibrillation may be performed as needed + Outcome Download Section PDF Listen +++ +++ Follow-Up ++ Monitor cardiac rhythm Monitor core temperature (esophageal preferred over rectal) often during and after initial rewarming to avoid recurrent hypothermia +++ Complications ++ Metabolic acidosis Pulmonary edema Rhabdomyolysis Hyperkalemia Pneumonia Pancreatitis Ventricular fibrillation Hypoglycemia or hyperglycemia Coagulopathy Acute kidney injury Cardiac arrhythmias may occur, especially during rewarming +++ Prognosis ++ Most otherwise healthy patients may survive moderate or severe systemic hypothermia Prognosis is poor with Low pH (≤ 6.6) Elevated potassium (≥ 4.0 mEq/L or ≥ 4.0 mmol/L) Serious underlying condition (eg, chronic kidney disease) Treatment delay Extracorporeal life support has been shown to substantially improve survival of patients with unstable circulation or cardiac arrest Comatose patients have a high risk of aspiration pneumonia +++ Prevention ++ "Keep warm, keep moving, and keep dry" Arms, legs, fingers, and toes should be exercised to maintain circulation Wet clothing, socks, and shoes should be replaced with dry ones Caution must be taken to avoid Cramped positions Constrictive clothing Prolonged dependency of the feet Use of tobacco, alcohol, and sedative medications Exposure to wet muddy ground and windy conditions +++ When to Admit ++ Hypothermia patients must undergo close monitoring for potential complications. This is typically done during an inpatient admission or prolonged emergency department observation, depending on the comorbidities and home care situation Monitoring includes vital signs, temperature, cardiac rhythm, oximetry, serial examinations (including extremity cold-induced injuries), and serial laboratory studies (to exclude electrolyte abnormalities, kidney or liver dysfunction, cardiac ischemia, and infection) + References Download Section PDF Listen +++ + +Haverkamp FJC et al. The prehospital management of hypothermia—an up-to-date overview. Injury. 2018 Feb;49(2):149–64. [PubMed: 29162267] + +Klein LR et al. Endovascular rewarming in the emergency department for moderate to severe accidental hypothermia. Am J Emerg Med. 2017 Nov;35(11):1624–29. [PubMed: 28506506] + +Kulkarni K et al. Efficacy of head and torso rewarming using a human model for severe hypothermia. Wilderness Environ Med. 2019 Mar;30(1):35–43. [PubMed: 30737153] + +Pasquier M et al. An evaluation of the Swiss staging model for hypothermia using hospital cases and case reports from the literature. Scand J Trauma Resusc Emerg Med. 2019 Jun 6;27(1):60. [PubMed: 31171019] + +Singh A et al. Severe hypothermia in the Sunshine State. Cureus. 2019 Jul 6;11(7):e5088. [PubMed: 31516797] + +Zafren K. Out-of-hospital evaluation and treatment of accidental hypothermia. Emerg Med Clin North Am. 2017 May; 35(2):261–79. [PubMed: 28411927]