Carotid artery diameter, plaque morphology, and hematocrit, in addition to percentage stenosis, predict reduced cerebral perfusion pressure during cardiopulmonary bypass: a mathematical model

Abstract

Cerebral complications after cardiac surgery are a significant cause of morbidity, mortality, and financial cost. Numerous risk factors have been proposed to explain the risk of cerebral damage. Carotid artery disease has an important role. Percentage carotid artery stenosis is the only measure of carotid artery disease that is used by cardiac surgeons to determine the need for either a carotid endarterectomy and/or a higher pump perfusion pressure. Identification of patients through their carotid plaque morphology who might benefit from higher pump perfusion pressures or concomitant carotid endarterectomy may reduce cerebral morbidity and mortality. A mathematical model using finite element analysis was created to model the carotid artery vessel and its stenotic plaque. Analysis showed that the degree of carotid artery stenosis, the length of the carotid artery plaque, the diameter of the carotid artery, and the blood hematocrit all independently significantly affect the required pump perfusion pressure to maintain adequate cerebral perfusion during cardiopulmonary bypass (CPB). The results from a mathematical model showed that carotid artery diameter, carotid artery plaque length, and hematocrit, in addition to percentage stenosis, should be included in any thought process involving carotid artery stenosis and cardiac surgery. Estimating cerebral risk during CPB should no longer rely on only the percentage stenosis.

Figure 1.

Diagrammatic representation of carotid plaque. D, diameter of carotid artery; H, height of plaque; L, length of plaque.

Figure 3.

Pressure drop across the plaque for carotid artery stenosis between 50% and 80%. It can be seen that carotid artery diameter has a significant effect on the required perfusion pressure because as the carotid artery diameter decreases from 10 to 5 mm, the pressure drop across the plaque markedly increases.

Figure 2.

Pressure drop across plaque in mmHg vs. percentage carotid artery stenosis. It can be seen that the length of the carotid plaque makes a significant difference to the required perfusion pressure.

Figure 4.

Effect of hematocrit on the pressure drop (mmHg) across the carotid artery plaque, for a carotid artery stenosis between 50% and 90%, depends on the length (1 vs. 5 cm) of the carotid plaque stenosis. It can be seen that as the hematocrit rises, the pressure drop across the plaque increases exponentially for a given carotid artery stenosis. hct, hematocrit; L, length of plaque.