Managing a Patient With Hypothermia

What is hypothermia?

Hypothermia is present when the body temperature is below 35-degrees Celsius (or 95-degrees Fahrenheit). It occurs when the body loses more heat than it creates or absorbs through external means and it has significant effects on physiology. Though hypothermia is usually a result of exposure to cold it can also be due to medical conditions and some medications.

How does the body regulate temperature?

Temperature is regulated by the hypothalamus, which receives input from thermal receptors throughout the body. When the hypothalamus detects a drop in body temperature, the initial response is to try to produce adequate body heat through shivering, increased muscle tone, and increases in the basal metabolic rate. Specific changes that occur include peripheral vasoconstriction and increases in hormones such as epinephrine and thyroid hormones. Behavioral changes also occur as body temperature drops which lead the individual to add more clothing, seek heat sources, and increase activity. 

Medical conditions that can cause hypothermia

Though hypothermia is most often due to cold exposure, it can be a result of certain medical conditions:

• Myxedema coma – Long-term hypothyroidism that is not adequately treated can lead to disruptions in the body’s ability to maintain homeostasis, and this includes temperature regulation.
• Hypoglycemia – Since the body uses blood glucose as a source of energy, hypothermia can result when blood glucose levels are significantly low.
• Burns – With large burns, the body’s protective layer is disrupted which leads to loss of body heat. This is why burn units are kept much warmer than other units in the hospital.
• Neurological conditions – Neurological injury and neurodegenerative disorders can disrupt the hypothalamus leading to impaired temperature regulation.
• Mental health disorders – Individuals with mental health disorders, including dementia and substance abuse disorders, may not display appropriate behavioral responses to cold stress.

Medications that can cause hypothermia

Sometimes hypothermia can be caused (or exacerbated) by certain medications, especially when taken together or taken in excess:

• Antipsychotics – Antipsychotic medications such as olanzapine and clozapine have been shown to cause hypothermia, especially in individuals with other risk factors such as older age, hypothyroidism, stroke, or renal disease.
• Anti-seizure medications – Some anti-seizure medications such as valproic acid can impair the body’s ability to regulate temperature, thereby leading to hypothermia.
• Benzodiazepines, opioids, and tricyclic antidepressants – Medications such as lorazepam, morphine, and amitriptyline can cause hypothermia due to disruptions in thermoregulation, especially with overdose.
• Lithium – Lithium toxicity can lead to reduced core body temperature.
• General anesthetics – Anesthesia inhibits the hypothalamus and causes peripheral vasodilation, both of which make it difficult for the body to respond appropriately when exposed to cold. Note that operating rooms are often kept on the cooler side for infection prevention purposes, so treating hypothermia in the recovery period is vitally important.
• Oral antidiabetics – Medications that lower blood sugar can impair the body’s ability to generate heat from glucose, thus impairing the body’s ability to compensate when exposed to cold temperatures. 
• Alpha-adrenergic agonists and beta blockers – These medications block the SNS which can blunt the body’s ability to compensate for cold exposure.

In addition, alcohol can also lead to hypothermia during cold exposure due to impaired shivering, hypoglycemia, peripheral vasodilation, and hypothalamus dysfunction.

Measuring body temperature 

To evaluate hypothermia accurately, it’s important to measure the body’s core temperature, which is the temperature of the internal organs. There are several ways to measure core temperature, but the most accurate methods are through a pulmonary artery catheter or esophageal thermometer. Pulmonary artery catheters are quite invasive and not often used. Esophageal thermometer probes are placed near the level of the heart to show the temperature of the myocardium. Note that this method is only only used in sedated or unconscious patients since it can stimulate the gag reflex and cause vomiting and aspiration. 

Other forms of core temperature measurement you will see used for hypothermic patients are: 

• Bladder temperature – Some Foley catheters are equipped with temperature sensors, which enables you to measure body temperature continuously. The evidence shows that as long as urine flow is within a normal range, then bladder temperatures align closely with core body temperature. Note, however, that it is most accurate in states of normothermia because bladder temperatures react to changes in core body temperature more slowly than esophageal measurements do.
• Rectal temperature – Studies show that rectal temps do not correlate well with core body temperature and readings can take longer to reflect changes than when compared to esophageal measurements. Challenges with rectal temperature include hardened stool in the rectum (which makes correct placement difficult), and discomfort for the patient (the probe must be inserted at least 15 cm into the rectum so that it is near the large arteries of the pelvis. And, in patients with hemodynamic compromise, rectal temperatures read lower than true core temperature.
• Nasopharynx – This location is able to provide reliable measurements of core temperature and is most commonly used during surgical procedures. The probe is inserted to a depth of 10 to 20 cm in adults so it lies near the internal carotid artery.  

Signs and symptoms of hypothermia

Hypothermia can be subcategorized into three stages – mild, moderate, and severe. In general, hypothermia causes the body’s physiologic functions to slow, though there can be some compensatory mechanisms occurring early on in mild hypothermia. Compensatory mechanisms are underlined in the descriptions below:

• Mild hypothermia (35 to 37 degrees Celsius) – Confusion, impaired judgment, slurred speech, ataxia, tachycardia, tachypnea, shivering, hyperglycemia, diuresis, ileus, impaired clotting (low platelets), DIC
• Moderate hypothermia (32 to 35 degrees Celsius) – Hallucinations and lethargy, bradycardia that is not responsive to atropine, hypotension, decreased cardiac output, diuresis, arrhythmias, hypoventilation, muscle rigidity, decreased shivering
• Severe hypothermia (28 to 32 degrees Celsius) – loss of thermoregulation ability, coma, absent ocular reflexes, continued deterioration in blood pressure and cardiac output, ventricular fibrillation, asystole, pulmonary edema, apnea, oliguria, “pseudo-rigor mortis” (patient may appear dead), impaired glucose (hypo or hyperglycemia)

To summarize, some key things you are watching for with your hypothermic patient are clotting abnormalities, cardiac arrhythmias, pulmonary edema, and hemodynamic compromise.

How do we treat patients with hypothermia?

The key treatment for hypothermia is stopping further heat loss and rewarming the patient. Additional treatments are aimed at addressing complications, including cardiac dysfunction and DIC, and maintaining a patent airway.

The first priority in treating the hypothermic patient is to stop the heat loss. If the patient was in water, remove wet clothing and dry the patient. If the patient is taking medications that induce hypothermia, those medications will likely be stopped and alternatives considered. The next key step is rewarming the patient, and several options are available depending upon the level of hypothermia:

• Mild hypothermia – If the patient has intact thermoregulation, which is generally indicated by shivering), then heated blankets and warm PO fluids are generally enough to increase core body temperature to safe levels. In general, a rate of 0.5 to 2-degrees Celsius per hour is recommended.
• Moderate hypothermia – External rewarming is often utilized in patients with  moderate hypothermia. Treatments include forced warm air (warming blankets) or heat packs placed on the chest, back, and axillae.
• Severe hypothermia – Internal or core rewarming is necessary in patients with severe hypothermia. There are several options available for core rewarming:
  • Warmed IV fluids between 40 and 42-degrees Celsius. In cases of significant blood loss, warmed blood products may also be utilized.
  • Heated lavage of the pleural or peritoneal space. These are invasive procedures that require the placement of tubes, so they can take some time to initiate.
  • Heated and humidified oxygen via endotracheal tube or oxygen mask (also helps prevent heat loss through respiration).
  • Extracorporeal core rewarming (ECR) includes hemodialysis, continuous arteriovenous rewarming, extracorporeal membrane oxygenation (ECMO), and cardiopulmonary bypass. Of these, hemodialysis is the most commonly used as it is widely accessible, though it’s important to note the patient’s blood pressure must be high enough to tolerate the procedure. Hemodialysis can increase core body temperature by 2 to 3-degrees Celsius per hour.

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Last Updated on December 4, 2024 by Maureen Osuna, MSN, RN