Hypothermia: Clinical sciences

Hypothermia is defined as a core body temperature of less than 95 degrees Fahrenheit or 35 degrees Celsius. It occurs when your body expends more heat than it creates typically due to prolonged exposure to cold, like getting stuck in a snowstorm or losing heat in homes during the winter. Based on the core temperature, hypothermia is divided into mild, moderate, and severe hypothermia. Regardless of the severity, hypothermia puts the individual at a very high risk of becoming hemodynamically unstable and is life-threatening, so it must be managed promptly.

you should first perform an ABCDE assessment. Acute management should be started immediately to stabilize the patient's airway, breathing, and circulation. Next, obtain IV access and consider starting warmed IV fluids. Next, put your patient on continuous vital sign monitoring, including body temperature, blood pressure, heart rate, and pulse oximetry, as well as cardiac telemetry! Finally, if your patient is in cardiac arrest, manage according to ACLS guidelines.

obtain a focused history and physical examination, as well as a 12-Lead ECG. Your patient will have a history of prolonged cold exposure. History could also reveal risk factors like a history of alcohol use, older age, or that your patient is experiencing homelessness; they may also have severe manifestations of psychiatric conditions, like mania or psychosis.

Physical examination will reveal a core temperature lower than 95 ºF or 35ºC, as well as hyperventilation initially, and may progress to hypoventilation as core temperature continues to decrease. In addition, you may notice shivering, but keep in mind that shivering will eventually stop if exposure to cold continues, and your patient may also develop confusion, lethargy, and reduced responsiveness.

The ECG may reveal sinus tachycardia initially, or progress to sinus bradycardia or a junctional rhythm. Keep in mind that junctional rhythm can be distinguished from a sinus bradycardia by the absence of P waves! Additionally, you might notice Osborn waves, also known as J waves, which refer to positive deflections at the junction between the QRS complex and ST segment! Osborn waves are most noticeable in precordial leads such as V3, V4, V5, and V6, and their height roughly correlates with the severity of hypothermia. In more severe cases, the ECG may even reveal ventricular arrhythmias or even asystole.

Here’s a clinical pearl to keep in mind! If your patient’s vital signs or level of consciousness do not match the degree of hypothermia, consider an underlying medical condition, such as infection, trauma, or metabolic conditions, like hypothyroidism, adrenal insufficiency, and hypoglycemia. For example, your patient might present with decreased responsiveness, hypotension, bradycardia, and mild hypothermia, which refers to a core temperature of 90 to 95ºF or 32 to 35 ºC! In this case, you need to order additional laboratory tests, like a CBC and CMP, to identify an underlying cause.

Ok, so if your patient presents with these signs and symptoms, you can diagnose hypothermia. Now, once you diagnose hypothermia, your next step is to assess the degree of hypothermia by measuring the patient’s core temperature. You should measure the patient’s core temperature using a low-reading thermometer, because standard thermometers cannot accurately measure a core temperature below 95 ºF or 35 ºC. The most accurate location to obtain a core temperature is the lower one-third of the esophagus due to its proximity to the heart. However, this requires the passage of an esophageal probe and may not always be practical, so it’s more common to obtain a core temperature from the bladder and rectum.

if the patient’s core temperature ranges between 90 and 95ºF, or 32 and 35ºC, you can classify it as mild hypothermia, so begin passive external rewarming. This includes removing the patient out of the cold if possible, removing any wet clothing, and covering the patient with a blanket or dry garments. If the patient doesn’t respond to passive external rewarming, consider active external rewarming with warm blankets, heating pads, warm baths, or forced warm air.