Monitoring: Equipment and Computers
Principle and Goal of study: During cardio-pulmonary bypass (CPB), mixed venous oxygen saturation (SvO2) has been traditionally used as an indicator of whole body oxygen supply/demand. Recently, the INVOS monitor has been used for non-invasive and direct assessment of cerebral blood oxygen saturation (RsO2). This study was undertaken to compare RsO2 and SvO2 during hypothermic hemodilution CPB.
Materials and Methods: Fourteen patients undergoing elective cardiac surgery using hypothermic hemodilution CPB were included in the study. During CPB, RsO2 and SvO2 were continuously monitored with a cerebral oximeter (INVOS 5100B) via a surface electrode placed on the patient's forhead and with the mixed venous oximeter (Bently Oxy-Sat meter) integrated in the cardiopulmonary bypass machine (Sarns 5000) respectively. Mean ± SD of RsO2, SvO2, PaCO2, Hct, and CO were determined during prebypass and during CPB at 31°C and 35°C. Statistical analysis were performed with the analysis of variance (ANOVA) and level of significance was considered at p < 0.05.
Results: Data (Mean ± SD) are shown in the table:
Conclusions: During hypothermic CPB, there was a significant increase of SvO2 associated with a paradoxical decrease of RsO2. The decrease in RsO2, despite the decreased cerebral oxygen consumption during hypothermic CPB, may be attributed to the possibility of decreased cerebral oxygen supply secondary to the α-stat strategy of CO2 management which decreased temperature-corrected PaCO2 during hypothermia down to 26.8 ± 3.1 mmHg.
1 Baraka A. et al. J Cardio Anesth 1990; 1: 35-38.
2 Holzschuf M. et al. Neuro Res 1997; 19: 246-248.