Radiographic and Other Studies

1. Chest x-ray. Look for pulmonary edema or aspiration.

2. Continuous ECG monitoring. Rule out cardiac dysrhythmia.

3. CT scan. Used to rule out intracranial or intra-abdominal process, especially in suspected trauma patients.

4. Neck x-rays. Often needed in patients with suspected head or neck trauma to evaluate the cervical spine.

V. Plan. Management must address the underlying condition impairing thermoregulation that led to hypothermia. Hypothermic patients are at increased risk of refractory ventricular fibrillation, which may be provoked by rough handling, including chest compressions and electrical defibrillation. Aggressive volume resuscitation with isotonic fluids is a mainstay in treating hypothermia. Method chosen to rewarm patient must be tailored to the individual, and presence or absence of circulation is at least as important as patient's temperature. Most textbooks mandate active rewarming for core temperature < 28°C

(82.4°F). Patients should not be declared dead until they have been rewarmed to 32°C (89.6°F).

A. CPR. Initiate if patient is not breathing or is pulseless. Continuous ECG monitoring is necessary because pulses are very difficult to palpate in hypothermic patients. Defibrillation is typically unsuccessful until patient is warmed to 32°C (89.6°F). If initiated, CPR should be continued until patient is warmed to 32°C.

B. Passive Rewarming (Patients Who Are Shivering). Shivering mechanism is usually preserved if core temperature exceeds 30°C (86°F). As long as patient is shivering, passive rewarming techniques may be utilized. These include removing cold or wet clothing, transporting to a warm environment, and covering with dry blankets. Passive rewarming requires that patient have spontaneous heat production, which makes it useful only in mild cases of hypothermia.

C. Active Rewarming (Patients Who Are Not Shivering). Patients who are not shivering have lost their thermoregulatory drive and require active rewarming. Controversy exists over exact temperature at which to begin internal active rewarming. Decision should be made based on individual patient and institutional expertise.

1. External active rewarming. Includes techniques such as hot packs, heating lamps, and warm water baths. These techniques are familiar, inexpensive, and readily available. External active rewarming may result in rewarming shock, decreased core temperature (afterdrop), and ventricular fibrillation. Severe hypovolemia is common in hypothermic patients due to vascular leak and a profound cold diuresis. Heat applied externally restores circulation to the coldest part of the body, which dumps cold and stagnant blood into the core. This, combined with an already depressed myocardium, dilated vascular beds, and hypovolemia, can lead to vascular collapse and a drop in core temperature. External active rewarming is unlikely to be effective in patients who do not have adequate spontaneous circulation.

2. Internal active rewarming (core rewarming). Preferred for severe hypothermia or patients with absent or ineffective circulation. Common techniques include warm humidified oxygen, heated intravascular fluids, closed thoracic or pleural lavage with warm saline, and heated lavage of bladder, stomach, colon, or peritoneum. Open thoracotomy with mediastinal irrigation and extracorporal circulation with heating elements are also effective. Core rewarming requires invasive devices not always available at rural or community hospitals. These methods are advantageous in that they are very effective and they lessen the chance of rewarming shock, core cooling, and cardiac arrhythmias.

VI. Problem Case Diagnosis. The 4-year-old boy had mild hypothermia from environmental exposure. He maintained his ability to shiver and responded well to passive rewarming.

VII. Teaching Pearl: Question. Why are children at increased risk of developing hypothermia?

VIII. Teaching Pearl: Answer. Children have a relatively high body surface area to mass ratio, decreased subcutaneous fat, and limited thermogenic capacity, all of which contribute to an increased risk of developing hypothermia.

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