Specific measures for rewarming

First, further heat loss should be prevented. Nurses and physicians should be aware that the patient's body temperature may drop during transport or when dressings are being changed. An insulating aluminum blanket placed over the trunk can help to retain heat. Care should be taken to avoid prolonged exposure during radiography, catheter placement, or patient evaluation.

A protocol for rewarming a patient with accidental hypothermia is shown in Fig,, 1...

Fig. 1 Rewarming protocol for accidental hypothermia. In addition to this rewarming protocol, the diagnosis should be confirmed, the temperature measured, aggravating factors should be eliminated, cardiovascular and respiratory functions should be supported, and the temperature, heart rate, blood pressure, and respiratory rate should be monitored. If the rewarming process fails (i.e. the temperature rises by less than 0.5 °C/h or decreases), one should go to the next step, i.e. active rewarming.

Passive rewarming is usually all that is required to treat mild hypothermia. These patients are conscious with no hemodynamic instability and no respiratory failure. Treatment is simple and includes wrapping in an insulating blanket, inhalation of a heated and humidified oxygen-air mixture through a face mask, hot drinks, and, if indicated, warmed infusions. In athletic patients, rewarming occurs within 1 h. In patients with comorbid conditions (cardiomyopathy, respiratory failure, malnutrition, etc.), achievement of normothermia may take longer, requiring adjunctive measures. The same is true when thermoregulation is impaired. In unconscious patients, the warmed humidified oxygen-air mixture can e delivered through an endotracheal tube. If this method fails, i.e. the temperature rises by less than 0.5 to 1 °C/h or decreases, more invasive methods are required. Gastric lavage may be initiated. External active rewarming using forced air may be tried, provided that there is no hemodynamic instability and fluid resuscitation can be performed aggressively.

In cases of moderate hypothermia, particularly if the body temperature is below 30 °C, the shivering capacity disappears and rewarming should be active. In unconscious victims with no hemodynamic instability, a warmed humidified oxygen-air mixture is given via an endotracheal tube, warmed solutions are infused intravenously, and gastric lavage is attempted. If there is no increase in temperature, peritoneal irrigation, pleural lavage, or extracorporeal warming should be instituted, possibly with external active rewarming.

In cases of moderate hypothermia with hemodynamic instability, body cavity lavage, hemodialysis, or continuous arteriovenous or venovenous warming should be started sooner, particularly when the body temperature is 28 °C. In cases where dialysis is required, such as renal failure, hyperkalemia, or removal of other toxins, peritoneal irrigation or hemodialysis should be used.

Active internal core-rewarming methods are mandatory with severe hypothermia. Peritoneal irrigation, pleural lavage, and/or extracorporeal rewarming should be commenced in addition to administration of a warmed humidified oxygen-air mixture through an endotracheal tube, warmed irrigation, and intravenous fluids and gastric lavage. The goal is to raise the temperature rapidly to about 30 °C, thus minimizing the chance of life-threatening arrhythmias. The ideal rewarming method for hypothermic patients with cardiac arrest is cardiopulmonary bypass.

When the temperature falls below 20 °C, the patient is in cardiocirculatory arrest with non-reactive pupils and rigid trunk and extremities. Aggressive treatment should be undertaken. Endotracheal intubation may be difficult due to jaw rigidity and a surgical airway is sometimes required. Mechanical ventilation with warmed humidified gas is administered at a low rate (2-4 breaths/min). Cardiac massage is probably inefficient, and should be reserved for those in asystole. Intravenous access requires a central route. Immediate cardiopulmonary bypass may successfully rewarm and resuscitate patients after prolonged cardiac arrest. Extreme hyperkalemia may be used as an indicator of futility, although precise upper limits incompatible with life have not been established.

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