Computer simulation of microscopic cerebral air emboli absorption during cardiac surgery.

Microscopic cerebral arterial air emboli (MCAAE) cause neurologic injury during cardiac surgery. We used a mathematical model of gas absorption to gain a preliminary assessment of what physical or physiologic parameters affect MCAAE absorption in the setting of cardiac surgery with its unique set of normal values. Simulated MCAAE of radii 50 and 200 microns have absorption times of 2 and 32 min, respectively. Predicted absorption times depend dramatically on PaN2. MCAAE are predicted to be absorbed twice as quickly at a PaN2 of 0 vs. 380 mmHg (FiO2 approximately equal to 0.50). Moderate hypothermia (27 degrees C) is predicted to cause only small decreases in absorption time. Changes in cerebral blood flow (for example, as affected by hemoglobin concentration, PaCO2, PaO2, collateral circulation, anesthetics, or cerebral metabolism) probably have only small effects on absorption time. Intravascular perfluorocarbons are predicted to cause small-to-moderate decreases in absorption time. In conclusion, there is probably only one important determinant of MCAAE absorption time during normothermic or moderately hypothermic CPB: arterial nitrogen partial pressure.