CO2 reactivity in the patients with extracorporeal circulation under mild hypothermia

We have evaluated cerebral blood flow velocities (CBFV) on transcranial Doppler (TCD) during cardiovascular surgery under extracorporeal circulation. We determined CO2 reactivity by varying the concentration of inspired CO2 and measuring CBFV with TCD. [Materials and methods] A total of 84 patients (36 women and 34 men, mean age; 64.0 ± 14.0 years old) were assessed. Of these, 14 patients had a history of suffering ischemic strokes. TC-2 64 (EME) with a 2 MHz Doppler probe was employed. The deep body temperature was maintained about 27 ℃ and the blood volume was fixed to 2.6 L/min/m2 . PaCO2 were monitored at every 10 min and CBFVs (MCA) were measured continuously. [Results] There were significant linear correlations between PaCO2 and CBFVS in the younger patients (under 70 yo) without ischemic heart disease (IHD). In the younger patients with IHD, there were only loosely correlations between PaCO2 and CBFVs. The CBFVs had no correlations with PaCO2 during extracorporeal circulation in the patients aged 70 or more. In the patients with ischemic strokes, there were no correlations between PaCO2 and CBFVs. [Conclusions] CBFV on TCD could be used as a indicator of the changes in the cerebral blood flow in the patients under controlled physical conditions.