Quantification and distribution of cerebral emboli during cardiopulmonary bypass in the swine - The impact of Pa-CO2

Background Patients undergoing cardiac surgery have a substantial incidence of neurologic complications related to cerebral embolization during cardio pulmonary bypass. The purpose of this study was to determine if adjustments In the arterial carbon dioxide (Pa-CO2 level can reduce cerebral and ocula r embolization, Methods: Twenty pigs underwent cardiopulmonary bypass at 38 degrees C. At e ither hypercarbia (Pa-CO2 = 50-55 mmHg, group H, n = 10) or hypocarbia (Pa- CO2 = 25-30 mmHg, group L, n = 10), an embolic load of 1.2 x 10(5) 67-mu m orange fluorescent microspheres was injected into the aortic cannula. Befor e and after embolization, cerebral and ocular blood flows were determined a t normocapnia using 15-mu m fluorescent microspheres. After cardiopulmonary bypass was completed, the eyes were enucleated and brain tissue samples we re collected. Microspheres were Isolated and the fluorescence was measured. Results: In groups H and L, the mean Pa-CO2 values at embolization were 52 +/- 3 mmHg and 27 +/- 2 mmHg, respectively(P < 0.0001), Total and regional embolization were significantly less in hypocapnia than in hypercapnic anim als: 142% more emboli were detected in the brain in group H than in group L (P < 0.0001). Cerebral blood flow after embolization was unchanged in Both groups. Similarly, fewer ocular emboli occurred in hypocapnic animals than in hypercapnic animals (P = 0.044), but in contrast to the brain, ocular b lood flow decreased significantly in both groups after embolization. Conclusions: Cerebral embolization is determined by the Pa-CO2 at the time of embolization, In cardiopulmonary bypass practice, reductions in Pa-CO2 d uring periods of embolic risk may reduce the risk for brain injury.