Rationale:

• Significant respiratory and metabolic acidosis is a common finding in moderate and severe hypothermia.
• Acute renal failure may occur following rewarming from accidental hypothermia.
• Hypothermia-induced diuresis increases the blood hematocrit and decreases plasma volume, which may be further exacerbated in elderly or malnourished patients.
• Repeat measurements of electrolytes are essential to avoid severe cardiac arrhythmias related to hyperkalemia or hypokalemia.
• Patients with acute hypothermia can present with either hypoglycemia or catecholamine-induced hyperglycemia.
• Hypoglycemia is one of the causes of hypothermia.

Evidence:

• Patients at extremes of age and those with underlying medical conditions are at greatest risk of hypothermia-related complications. Lab data will assist in determining the severity of illness, choice of rewarming technique, and management of rewarming (59; 112; 113; 114).

Comments:

• As the rewarming process proceeds, one should continually measure and treat abnormal arterial blood gases, electrolytes, hematocrit, and serum glucose concentrations to prevent any major metabolic disturbance or hemodynamic catastrophe from ensuing.
  • Because hypothermia suppresses insulin secretion, the hyperglycemia seen in hypothermic patients may correct spontaneously during rewarming (115).
• Rewarming rats after experimental hypothermia results in ultrastructural changes in the kidney resembling acute tubular necrosis (116).
• The hypovolemia and dehydration resulting from cold-induced diuresis should be corrected to limit the risk of afterdrop during the rewarming process. Correct interpretation of the blood gases should account for the patient's temperature, because the solubility of oxygen and carbon dioxide increases at lower temperatures, so that the partial pressure of both oxygen and carbon dioxide, measured at body temperature, decrease as the temperature decreases.
• Blood gas analysis of a hypothermic patient must be corrected mathematically to obtain in vivo pH and arterial carbon dioxide pressure (PaCO ₂). During hypothermia induced for cardiothoracic surgery, acid-base status routinely is managed by using the alpha-stat (temperature uncorrected) method or the pH-stat (temperature corrected) method. It remains controversial as to which method is superior.
  • Accumulating evidence favors the pH-stat approach because of its favorable effect on the cerebral circulation (117; 118; 119; 120), although superior outcomes thus far have been shown only in children (119). In one single-center trial, pH-stat and α-stat management invariably yielded better outcomes depending on the type of cardiothoracic surgery, but, in aggregate, neither method proved superior (121).