中等度低体温体外循環時のｔｒａｎｓｃｒａｎｉａｌ Ｄｏｐｐｌｅｒによる脳血管ＣＯ２反応性の評価

Abstract

We have evaluated cerebral blood flow velocities (CBFV) using transcranial Doppler (TCD) during cardiovascular surgery under extracorporeal circulation. We attempted to determine cerebrovascular reactivity to CO2 pressure by varying the concentration of inspired CO2 and measuring CBFV with TCD under moderate hypothermia. In this study, 66 patients (mean age: 63.6±7.2 years) who underwent cardiac operations were assessed over a four-year period. Forty patients received aorto-coronary bypass grafts, 13 patients had valvular heart disease, and 12 had congenital septal defects. One patient had a left atrial myxoma. In all cases, cardiac surgery was performed with moderate hypothermia and non-pulsatile cardiopulmonary bypass. The pump flow was fixed at 2.6 L/min/m2 in all patients.Patients were divided into three groups according to age (cut-off value, 70 years) and type of surgery. Among the 41 patients under 70 years old, 15 patients underwent closure of septal defects or replacement of heart valves (non-CABG group), and 26 received coronary arterial bypass grafts (CABG group) . All of the 25 patients aged over 70 years received CABGs (elderly group) . As in the non-CABG group, there was a close correlation between PaCO2 and mean CBFV (mean CBFV=-2.47+1.21×PaCO2, R2=0.429) . The patients in the CABG group showed a mild linear correlation between PaCO2 and mean CBFV (mean CBFV=1.64+0.89×PaCO2, R2=0.216) . There were no significant correlations in the elderly group.It is concluded that flow velocity is increased under moderate hypothermia in proportion to increased PaCO2 in patients aged under 70 years. TCD is a practical non-invasive monitoring system and can provide an approximation of changes in cerebral circulation during moderate hypothermia.