Computer simulation of brain cooling during cardiopulmonary bypass.

A mathematical model of heat transport was used to analyze the effects of convection, metabolism, and conduction on the rate of brain cooling and the final brain temperature during cardiopulmonary bypass. Convection, a function of cerebral blood flow and arterial blood temperature, is by far the most important process to determine the rate of brain cooling. Arterial blood temperature almost entirely determines the final brain temperature. Although conduction (head surface cooling) has little effect on the rate of brain cooling or final brain temperature in adults, it may have moderate effects in infants. Brain metabolic heat production has insignificant direct effects on the rate of brain cooling and final brain temperature in both adults or infants. Computer simulation of convective cooling of the adult brain to 27 degrees C shows that, with routine perfusion techniques, brain temperature equilibration is rapid (16 minutes) and small brain-blood temperature gradients are achieved. Simulation of infant brain cooling to 17 degrees C shows that, to avoid excessive brain-blood temperature gradients, 22 to 26 minutes may be required to achieve brain temperature equilibration.