Treatment includes both general supportive measures and specific rewarming techniques.345 and 6 Therapy begins with careful, gentle handling, since manipulation can precipitate ventricular fibrillation in the irritable hypothermic myocardium.

Controversy has arisen regarding the performance of CPR on an unmonitored patient who appears to be profoundly hypothermic and in cardiopulmonary arrest. Opponents of CPR argue that pulses may be difficult to detect in this setting and that chest compressions may precipitate ventricular fibrillation. They recommend withholding CPR until the presence of an arrested rhythm (ventricular fibrillation or asystole) is confirmed. Alternatively, withholding CPR in the patient who is truly in cardiac arrest may unnecessarily subject the brain and other organs to prolonged ischemia. This CPR controversy applies only to patients with severe hypothermia, with core temperatures less than 28°C (82.4°F); practically, it may be difficult to confirm this diagnosis in the field. To avoid inappropriate chest compressions, prehospital care personnel should examine the patient for 30 to 60 s before diagnosing pulselessness. If no pulses are detected, most physicians recommend initiating CPR. The optimal rate of chest compressions and ventilations has not been determined.

Similar considerations apply to monitored patients. Some authors recommend avoiding chest compressions in severely hypothermic patients with "nonarrested rhythms" (sinus bradycardia, artrial fibrillation with slow ventricular response, junctional rhythms), even without a palpable pulse. Most, however, recommend full CPR in patients with pulseless electrical activity, even with profound hypothermia.

Oxygen and intravenous fluids should be warmed, and patients should have constant monitoring of their core temperature, cardiac rhythm, and oxygen saturation. Pulse oximetry is usually accurate in hypothermic patients,10 although unreliable data may be obtained with profound vasoconstriction or a very low cardiac output. If central venous lines are placed, care should be taken to avoid entering and irritating the heart. In general, indications for endotracheal intubation are the same as in the normothermic patient. Concern has been raised regarding induction of dysrhythmias during intubation; however, there is a very low complication rate with careful intubation after oxygenation.11

Although dysrhythmias in the hypothermic patient may represent an immediate threat to life, most rhythm disturbances (e.g., sinus bradycardia, atrial fibrillation or flutter) require no therapy and revert spontaneously with rewarming. In addition, the activity of antiarrhythmic and cardioactive drugs is unpredictable in hypothermia, and the hypothermic heart is relatively resistant to atropine, pacing, and countershock.

Ventricular fibrillation may be refractory to therapy until the patient is rewarmed. The American Heart Association's 1992 guidelines suggest initial defibrillation attempts with up to three shocks. If this is unsuccessful, CPR should be instituted and rapid rewarming begun. Defibrillation should be reattempted as the core temperature rises. Bretylium has been suggested as the drug of choice for the prophylaxis or treatment of ventricular fibrillation in hypothermic patients, although data concerning its efficacy are conflicting. —I3

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