Hypothermia is a complex issue in the management of the potential abdominal organ donor. Failure to correct hypothermia can delay certification of brain death with further deterioration of the patient. Following establishment of brain death, hypothermia may result from the inability of the patient to shiver and thereby compensate for heat losses as well as failure of vasoconstriction. Iatrogenic causes of hypothermia include resuscitation with large volumes of unwarmed fluids and blood products and conductive and convective heat loss to the environment. A liter of crystalloid at a room temperature of 20°C will lower a 70 kg patient's temperature by 0.25°C, a unit of blood (250 ml) at 4°C will lower body temperature by 0.125°C.
Hypothermia has a number of adverse consequences in the organ donor. Chief among them is resultant myocardial depression. This can progress to cardiac arrest. Decreased oxygen delivery can also occur due to shifting of the oxyhemoglobin dissociation curve to the left. At temperatures less than 32°C coagulopathy can occur. Fluid losses may also be exacerbated as hypothermia decreases renal tubular cell reabsorptive function with a resultant "cold diuresis".
Prevention of hypothermia is therefore extremely important. Convective heat losses result from high turnover of cool air in air-conditioned intensive care areas.
The relative humidity can also exacerbate heat losses. Conductive losses occur through exposure to wet drapes and cool surfaces. Heat loss may also result from evaporation of surgical prep solutions applied for line placement or cardiac catheterization. Core temperature must be monitored. Because of the loss of thermoregulation, skin temperature is the least reliable measure of core temperature. Esophageal, rectal or bladder probes or tip of a pulmonary artery catheter are much more reliable measures of core temperature.
Treatment of hypothermia involves covering exposed surfaces, use of a warming blanket, adding heated humidifiers to the anesthetic circuit, warming of administered fluids and raising room temperature and humidity.
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