BRAIN HYPERPERFUSION DURING CARDIAC OPERATIONS - CEREBRAL BLOOD-FLOW MEASURED IN MAN BY INTRA-ARTERIAL INJECTION OF XE-133 - EVIDENCE SUGGESTIVE OF INTRAOPERATIVE MICROEMBOLISM
Cerebral blood flow (CBF) was measured by intra-arterial injection of 133Xe in 29 patients during cardiac operations. Marked changes occurred in all patients. A normal and significant correlation with temperature and plasma PCO2 [partial pressure CO2] (P < 0.01) support the relability of the method. Mean CBF measured between sternotomy and the onset of extracorporeal circulation (ECC) was 38 ml/100 g .cntdot. min. The 1st min of ECC was associated with a decrease in CBF in 9 of 12 patients (P < 0.02). During steady-state hypothermic ECC (temperature 29.degree. C), CBF increased unexpectedly to 64 ml/100 g .cntdot. min (P < 0.01). Following rewarming during steady-state normothermic ECC, mean CBF decreased to 42 ml/100 g .cntdot. min with signs of impairment of cerebral autoregulation. Ten and 20 min after termination of ECC, mean CBF was 40 and 41 ml/100 g .cntdot. min, respectively. Arterial PCO2 was found to be important in regulating CBF. The cerebral autoregulation maintained CBF down to arterial pressures of around 55 mm Hg. Below this level, CBF was significantly correlated with perfusion pressure (P < 0.01). Multiple small emboli with a hyperemic border zone could cause a brain hyperperfusion, as seen in patients during bypass. Measurements of CBF during ECC hold promise as a guide toward safer cardiac operations.