Response of Cerebral Blood Flow and Metabolism to Changes in Arterial Carbon Dioxide Tension during Moderate Hypothermic Cardiopulmonary Bypass in Patients with Cerebrovascular Disease / 日本心臓血管外科学会雑誌

ABSTRACT

The purpose of this study was to examine the responses of cerebral blood flow and metabolism to changes in arterial carbon dioxide tension during moderate hypothermic cardiopulmonary bypass in patients with cerebrovascular disease undergoing open heart surgery. Computed tomography scan (CT) and single photon emission computed tomography (SPECT) were performed preoperatively for 17 patients. The patients were categorized according to their CT and SPECT findings. Ten patients were included in the normal group, 7 patients were included in the CVD group. Blood flow velocity in the middle cerebral artery (MCAv) was measured by means of transcranial Doppler ultrasonography at two different arterial carbon dioxide tensions (at a high PaCO₂ of 45-50mmHg, at a low PaCO₂ of 30-35mmHg, uncorrected for body temperature) during moderate steady-state hypothermic cardiopulmonary bypass. Simultaneously cerebral oxygen consumption was estimated by relating the arteriovenous oxygen content difference to flow velocity (D-CMRO₂). MCAv and D-CMRO₂ were expressed as percentages of the values determined at 30 minutes before cardiopulmonary bypass. In the normal group, a PaCO₂ of 47.4±2.5mmHg (mean±SD) was associated with an MCAv of 99.4±17.8% and a D-CMRO₂ of 53.4±25.5%, while a PaCO₂ of 33.7±1.3mmHg was associated with an MCAv of 64.3±18.1% and a D-CMRO₂ of 53.5±26.2%. In the CVD group, a PaCO₂ of 49.1±4.2mmHg was associated with an MCAv of 81.4±22.3% and a D-CMRO₂ of 34.0±19.4%, while a PaCO₂ of 33.6±1.3mmHg was associated with an MCAv of 54.7±23.8% and a D-CMRO₂ of 49.0±19.4%. We conclude that in patients with cerebrovascular disease cerebral blood flow is changed in response to changes in arterial dioxide tension during moderate hypothermic cardiopulmonary bypass, however a high PaCO₂ depresses cerebral oxygen consumption because hypercarbia may cause potentially harmful redistribution of regional cerebral blood flow away from marginally-perfused to otherwise well-perfused areas.