All patients should be given supplemental oxygen Patients with profuse secretions, respiratory depression, or impaired mental status should be intubated and mechanically ventilated Intubation should be performed as gently as possible to minimize the risk of arrhythmias A decreased metabolic rate produces less carbon dioxide, and usual minute ventilation would produce respiratory alkalosis, increasing the risk of dangerous arrhythmias Therefore, ventilation should begin at approximately one-half the normal minute ventilation Assessment of acid–base status and ventilation in the hypothermic patient is the subject of considerable confusion Blood gas machines heat the patient’s blood sample to 37°C (98.6°F) before measuring pH and gas partial pressures (thus providing theoretical values if the patient were 37°C [98.6°F]) If the patient’s actual temperature is provided with the sample, the machine can correct the values according to the nomogram of Kelman and Nunn ( Table 90.6 shows one set of guidelines for appropriate correction) However, it is important to understand two concepts The first is the ectothermic principle, which relies on the following aspect of physiology: dissociation of ions and partial pressures of gases are decreased in cooled blood In hypothermia, therefore, neutral pH is higher, whereas “normal” PCO is lower than is encountered at 37°C (98.6°F) For example, hypoventilation of the hypothermic patient with a pH of 7.5 would actually induce an undesirable respiratory acidosis A second, more practical concept is that if the patient’s blood volume is restored and oxygenation maintained, acidosis will be corrected spontaneously as the patient is warmed Heart rate and rhythm should be monitored continuously and the patient handled gently to avoid precipitation of life-threatening arrhythmias in an irritable myocardium Sinus bradycardia, atrial flutter, and atrial fibrillation are common but rarely of hemodynamic significance Spontaneous reversion to sinus rhythm is the rule when temperature is corrected It may be difficult to detect pulses in the hypothermic patient; therefore, it is important to provide chest compressions until pulseless electrical activity has been ruled out by echocardiography or arterial BP monitoring Ventricular fibrillation may occur spontaneously or with trivial stimulation, especially at temperatures less than 28° to 29°C (82.4° to 84.2°F) Electrical defibrillation is warranted but frequently is ineffective until core temperature rises Chest compressions should be initiated and maintained until the temperature is higher than 30°C (86°F), when defibrillation is more likely to be effective Fluid replacement is essential Relatively little plasma loss occurs in acute hypothermia but losses may be great in hypothermia of longer duration Normal