Rationale:

• Continuous monitoring during the rewarming of hypothermic patients will allow for early diagnosis and implementation of appropriate therapy to treat afterdrop, acidosis, or hemodynamic instability.

Evidence:

• Pathophysiologic effects of hypothermia and its complications can be life threatening and may require immediate intervention. Such interventions may include cardioversion for malignant ventricular arrhythmias, intubation and mechanical ventilation for respiratory failure, inotropic support for cardiogenic failure, dialysis for renal failure, and invasive rewarming strategies (37; 112; 138; 139).

Comments:

• Caution must be applied to the use of inotropic support in moderate to severe hypothermia. The rat model suggests that there may be differences in cardiac and vascular responsiveness to epinephrine during hypothermia compared to normothermia. Hypothermic rats that were given low-dose epinephrine (0.125 µg/min) during rewarming from 28°C (82.4°F) experienced a significant improvement in cardiac output, whereas the cardiac output remained unchanged compared to controls in rats given high-dose epinephrine (1.25 µg/min). During hypothermia, the increase in systemic vascular resistance produced by high-dose epinephrine appears to counteract its effect on cardiac inotropy (140).
• In canine models, even mild hypothermia depresses left ventricular diastolic function. Rapid intravenous infusion of warmed fluids could precipitate pulmonary edema in hypothermic patients, especially those who, through advanced age or long-standing hypertension, have underlying impaired ventricular compliance (141).
• A growing body of experimental data from laboratory animals suggest that mild hypothermia (approximately 33°C [91.4°F]) is neuroprotective in traumatic brain injury when achieved rapidly following the insult. However, the extent of neuroprotection also depends on the rate of rewarming following therapeutic hypothermia, with slow rewarming resulting in better outcomes. The neuroprotective effect of hypothermia combined with slow rewarming has been shown for contusion volume (142), responsiveness of the cerebral microcirculation (143), and the extent of axonal injury (144).