ADVANCING YOUR PRACTICE

Hypothermia: A hazard for all seasons
Mary Patricia Day, RN, CRNA, MSN

Dave Lindley, 35, is brought to your emergency department (ED) in the middle of the night by a motorist who'd found him wandering on the road during a snowstorm. Dave says he's cold and sleepy; you see he's shivering, he appears uncoordinated, and he's breathing rapidly. He doesn't know how long he was walking.

The owner of a landscaping and snow removal company, Dave had been plowing snow when his truck got stuck in a drift on a country road. His cell phone wouldn't work, so he started walking to find help.

Dave is suffering from hypothermia secondary to his exposure to the elements. Before I discuss how you'll treat him, let's review the pathophysiology and types of hypothermia.

Shiver me timbers
Hypothermia is a reduction in the normal core body temperature of 98.67° F (37.7° C) caused by an imbalance between the body's heat production and heat loss. This imbalance can be caused by exposure, reduced metabolism, or a defect in the body's thermoregulatory mechanism.

Accidental or unintentional hypothermia can be caused by cold-water submersion or prolonged exposure to cold weather, as in skiing accidents or accidents involving people who work or live outside. (Intentional hypothermia, which is used to treat neurologic disorders, is beyond the scope of this article.) Certain people are at greater risk for hypothermia even without exposure to extreme weather; for example, older adults, very young children, patients with traumatic injuries, and patients with hypothyroidism, malnutrition, drug overdose, or ketoacidosis.

In acute hypothermia, the body attempts to reduce heat loss by shunting blood away from the skin through peripheral vasoconstriction. Shivering, the body's attempt to increase the production of body heat, results from stimulation of the hypothalamus.

When core temperature drops to 93.2°F (34°C), coordination and thinking processes slow down. With further reduction in core temperature, the activity of the vital organs slows down. You'll see signs and symptoms of decreased cardiac output, conduction abnormalities on the electrocardiogram (ECG), reduced heart rate secondary to sinoatrial and atrioventricular nodal depression, decreased respiratory rate, and signs and symptoms of decreased cerebral perfusion.

Without treatment, hypothermia can lead to bradycardia and bradypnea so severe that the patient's heart rate and respirations may be undetectable. As hypothermia progresses, life-threatening cardiac dysrhythmias, such as ventricular tachycardia and ventricular fibrillation, may develop.

Estimating core temperature is an important diagnostic tool. Although tympanic membrane temperature measurements can be used, a rectal temperature is more reliable due to the abundant blood supply to the rectum. Once you know your patient's core temperature, you can classify his hypothermia. These classifications help guide treatment.

In mild hypothermia the patient's temperature ranges from 93.2°F to 96.8°F (34°C to 36°C). He may feel cold, shiver, and have signs and symptoms of peripheral vasoconstriction, such as pale, cool extremities and a feeling of numbness in his limbs. Bodily functions progressively slow down, causing sluggish coordination and responses. The patient may be lethargic, tachycardic, and tachypneic.

Moderate hypothermia, a core temperature of 86°F to 93.2°F (30°C to 34°C), is characterized by a depression of body systems. The patient's behavior—including decreased level of consciousness, confusion, slurred speech, and diminished reflexes—are consistent with decreased cerebral blood flow. The patient will have decreased respiratory rate, heart rate, blood pressure, and capillary refill time. He may have to urinate often; moderate hypothermia is characterized by a cold diuresis. As his core temperature drops, he stops shivering. You may notice some muscle rigidity.

Severe hypothermia is characterized by a temperature of less than 86°F (30°C). This condition is life-threatening because the patient may develop serious cardiac dysrhythmias, such as ventricular fibrillation and asystole. You'll also notice skin that's very cold to the touch, absent pupillary responses, and muscle rigidity. The patient's breathing is slow and at times difficult to detect. He'll have significant hypotension, and peripheral pulses may be undetectable. Unresponsive, he may appear dead.

For any patient with hypothermia and a perfusing cardiac rhythm, resuscitation efforts start with removing wet clothes and insulating him from further environmental exposure. Monitor his core temperature and cardiac rhythm, keep him in a horizontal position, and avoid rough movement and excess activity.

A patient with mild hypothermia may need only passive rewarming measures, such as moving him to a warm environment and providing him with warmed blankets or dry clothing and giving him warmed drinks or food. If he isn't fully alert, take precautions against choking.

Treating moderate hypothermia
Use active external rewarming measures for truncal areas to treat moderate hypothermia. The key here is not to increase the patient's temperature too fast. A rapid rise in body temperature can cause core temperature to drop secondary to peripheral vasodilation and the return of cold peripheral blood to the body's core, so limit temperature increases during the rewarming process to 0.5°F to 2.2°F (0.3°C to 1.2°C) an hour.

After performing the ABCs (assessing airway, breathing, and circulation), establish intravenous (I.V.) access. Obtain an ECG and blood specimens for lab work (including arterial blood gas [ABG] analysis), as ordered. Besides the interventions used to treat mild hypothermia, such as removing the patient's wet clothes, use active external rewarming measures on the patient's trunk only. This reduces the risk of temperature afterdrop and dysrhythmias during the rewarming process.

Following the manufacturer's recommended safe temperature range instructions, use a forced-air warming blanket to circulate warm air directly over the patient's skin. Throughout rewarming, continuously assess your patient's level of consciousness, core body temperature, cardiac rhythm, intake and output, and skin integrity. Monitor his blood glucose as ordered: Cold inhibits insulin release from the islets of Langerhans, posing a risk of hyperglycemia. Prolonged hypothermia can lead to hypoglycemia.

Treating severe hypothermia
Besides the previously mentioned interventions, treatments for severe hypothermia include active internal rewarming measures, such as administration of warmed humidified oxygen and warm I.V. fluids. Other treatments that may be used for urgent cases include peritoneal lavage with warmed fluids, pleural lavage with warm saline through chest tubes, extracorporeal blood warming with partial bypass, and cardiopulmonary bypass.

Patients with severe hypothermia and cardiac arrest may respond to cardiopulmonary resuscitation with internal warming measures. Follow the American Heart Association's recommendations, based on core temperature, to guide resuscitative efforts, including defibrillation if necessary. Be very careful when turning or moving your patient; because of his low temperature, rough movement or unnecessary activity can provoke ventricular fibrillation.

Auscultate breath sounds frequently because a patient with severe hypothermia is at high risk for developing pulmonary edema. The ED physician may decide to secure his airway with an endotracheal tube.

Repeated blood work may be ordered based on the patient's clinical condition. During repeat patient assessments, be on the lookout for potential complications of rewarming, including rewarming shock (a drop in blood pressure associated with fluid and catecholamine depletion), acidosis, and cardiac dysrhythmias.

Once your patient's core temperature is restored to normal, he'll be admitted to a monitored hospital bed and watched for short-term complications. After he's discharged home, he'll be monitored by his primary care provider (or other specialists, as appropriate) for long-term complications associated with hypothermia, such as heart failure, hepatic and renal failure, abnormal erythropoiesis, myocardial infarction, pancreatitis, and neurologic dysfunctions.

Back to Dave
On admission to the ED, Dave is alert and oriented, his airway is patent, and he's breathing rapidly on his own. He has prolonged capillary refill, indicating peripheral vasoconstriction. His temperature is 95°F (35°C) rectally. When he's asked to sign his name, you notice that he appears uncoordinated and can't hold the pen properly. He has no history of medical problems or falls, has no other injuries, and hasn't recently used drugs or alcohol.

You attach him to a cardiac monitor, which shows sinus tachycardia. His lungs are clear with equal bilateral breath sounds. Dave is diagnosed with mild hypothermia based on his core temperature and signs and symptoms. Depending on the ABG results, the ED physician may order humidified oxygen via nasal cannula.

You help Dave remove his wet clothing, cover him with warmed blankets, and establish I.V. access as you begin the rewarming process. Make sure the room is warm and keep Dave out of drafts. Place warm blankets or towels around his head and neck to facilitate rewarming.

As rewarming progresses, the physician decides that Dave can safely take fluids by mouth. You can give him small amounts of warmed clear fluids, after your assessment indicates that his coordination has improved and he can safely use a cup without choking or spilling (which poses a burn risk). With Dave's permission, you initiate an attempt to notify his family about his admission to the hospital.

Preventing problems
Because Dave's winter job is snow removal, he's at risk for future episodes of hypothermia. Before discharge, teach him how to protect himself in the future.

His outdoor clothing should include a hat, a face mask or scarf to cover his mouth and face, and a jacket with sleeves that are snug at the wrist (to retain body heat). Advise him to wear layers of loose-fitting clothing to help trap body heat. Wool or silk fabrics make good inner layers; outer layers should be tightly woven and wind-resistant. His shoes, jacket, pants, scarf, hat, and gloves should be water-resistant.

While he's working outside, Dave should try to stay dry and avoid overheating himself because evaporation of water, perspiration, or gasoline spilled on the skin accelerates heat loss. He should keep extra blankets, dry clothing, and newspapers (for insulation) in the passenger area of his truck. These can be used for warmth if necessary. He should also make sure his cell phone is fully charged. For more safety advice, see Tips for stranded motorists.

By promptly recognizing hypothermia and knowing how to respond, you can help patients like Dave receive proper treatment, recover fully, and avoid future episodes of hypothermia.

References

American Heart Association. 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 112(24, Suppl.):IV136-IV138, December 13, 2005.
Centers for Disease Control and Prevention. CDC Emergency Preparedness and Response. Winter Weather FAQS. http://www.bt.cdc.gov/disasters/winter/faq.asp. Accessed May 17, 2006.
Field JM, et al. (eds). Handbook of Emergency Cardiovascular Care for Healthcare Providers. Dallas, Tex., American Heart Association, 2006.
Phillips TG. Hypothermia. http://www.emedicine.com/med/topic1144.htm. Accessed May 17, 2006.
The Weather Channel. Driving Safety Tips. http://www.weather.com/activities/driving/drivingsafety/?from=secondarynav. Accessed September 29, 2006.

Source: Nursing2006. December 2006.