[The effect of preoperative factors on intraoperative oxyhemoglobin dissociation curve]

The position of oxyhemoglobin dissociation curve (ODC) expressed with P50, has a large influence on the oxygen supply. It has been reported that during hypoxia with increased oxygen demand, P50 can increase with a reduction in oxygen affinity. In this study, we investigated the effect of preoperative factors on intraoperative P50 and the relation between the P50 values of the mixed venous blood and those of internal jugular bulb venous blood in seventy patients for cardiac surgery. Preoperative reduction in percentage vital capacity (%VC) and reduced hemoglobin concentration were associated significantly with an increase in intraoperative P50 value. The P50 act (P50 value with only temperature adjusted to 37 degrees C) of the internal jugular bulb venous blood was significantly higher than that of mixed venous blood. These results suggest that intraoperative tolerance to hypoxia and the increase in oxygen demand might be reduced in patients with preoperative abnormality of %VC and the hemoglobin concentration. And this tolerance might be limited in brain.