Dr. Friederike (Fredi) Froke, D.O. is a PGY-1 in Emergency Medicine at Mayo Clinic EM residency program.
Diagnosis and management of hypothermia remains a priority concern by emergency medicine providers when caring for patients with cold exposure. Hypothermia is defined as a core body temperature found to be below 35 degrees Celsius (C).  Patients at high risk of cold exposure includes individuals with various behavioral response conditions such as dementia, alcohol or sedative intoxication, encephalopathy, undomiciled, immobility such as neonates or neuromuscular compromise.  There is significant morbidity as a result of hypothermia as it can lead to arrythmias, renal failure, encephalopathy, hepatoxicity, and coagulopathies.  Cold environmental exposure can also worsen cardiac and respiratory pre-existing conditions.  Even despite appropriate medical intervention the mortality of patients with moderate to severe hypothermia is about 50 percent. 
The body may experience losses in heat due to gradients created through radiation, conduction, and convection. Radiant heat loss is typically experienced through inadequate insulation, typically from the head which can result in over 50 percent reduction in heat. Conduction loss occurs in immersion exposures because of direct contact of the skin to a cooler fluid. Windchill causes a convection heat loss event as the wind carries heat from the individual. The body will attempt to compensate to the loss of temperature through shivering which can increase the basal metabolic rate up to five times, as mediated through thyroxine and epinephrine. The severity of hypothermia is categorized by the core temperature of the patient: mild (32-35 C), moderate (28-32 C), and severe (<28 C). Each category has been found to have differing clinical manifestations.  The Swiss staging system has categorized these findings based on severity of hypothermia (HT) in the table below:
Mild hypothermia demonstrates sympathetic excitation initially as observed through hypertension, tachycardia, and tachypnea. Fatigue will subsequently occur, and the patient will demonstrate ataxia, hypovolemia, and apathy. Moderate hypothermia is associated with atrial dysrhythmias, decreased heart and respiratory rate, hyporeflexia, and hypotension. J waves may also be observed on electrocardiograms at this temperature. As the core temperature lowers to severe hypothermia a patient may demonstrate non-reactive pupils, pulmonary edema, apnea, coma, ventricular dysrhythmias, and asystole. 
Assessing vital signs in a patient with cold exposure requires a nuanced approach. Monitoring the core temperature of a hypothermic patient may be difficult. Thermometers with the capability to read low temperatures are not widely available in all emergency departments . Core temperature monitoring can be obtained through rectal and bladder probe placement with understanding temperatures may lag in the setting of active rewarming. [2,8] Should the patient be intubated, appropriate temperature monitoring is with a probe in the lower third of the esophagus. It may be difficult to appreciate a peripheral pulse of the patient and should be observed for 60 seconds.
Patient assessment includes physical examination, trauma evaluation, and investigation of other illnesses which led to environmental exposure. Evaluation of the patient’s clinical status is initially completed by assessing airway, breathing, and circulation. All clothing is removed, and warming blankets should be in place. Labs include point-of-care glucose check, complete blood count, complete metabolic panel, and creatinine kinase.  Labs may demonstrate fluctuating potassium due to acid-base changes in rewarming. Creatinine can be elevated in the setting of acute tubular necrosis or rhabdomyolysis.  Every 4 hours an electrolyte reassessment should take place in moderate to severe hypothermic patients. Should point-of-care glucose testing be unavailable it is appropriate to provide a glucose trial as it is likely their glycogen stores are depleted. An EKG is needed due to association of hypothermia with dysrhythmias. The J point can be elevated, referred to as Osborne wave, and is seen in precordial leads. The most common arrythmia seen with cold exposure is atrial fibrillation.[7,8] Warmed IV fluids up to 42 degrees C can be administered to limit continued heat loss and the amount delivered should be based on volume status, electrolytes, and pH considerations. 
Triaging and managing hypothermic patients is well described in the figure below:
Patients recovering from mild hypothermia can be discharged home after rewarming. Patients with moderate to severe hypothermia will require admission managing systemic ramifications.  The clinical course of patients with moderate to severe hypothermia is difficult to predict. For example, a case report documents a patient with full neurologic recovery after treatment from accidental hypothermia with a core body temperature found to be 14 degrees Celsius. 
Hypothermia can be avoided through education and prevention efforts.  Direct exposure to the elements can be significantly lessened through wearing multiple layers of clothing with fabrics designed to retain heat such as wool, silk, and polypropylene. Insulated hats and scarves should be unitized to preserve heat which may be lost due to radiation energy transfer. If symptoms of hypothermia occur, the individual should return to indoors to prevent progression of cold exposure.