[The use of the Siggaard-Andersen model of the oxyhemoglobin dissociation curve in patients in the immediate period following open heart surgery].

A total of 300 patients have been examined on the first-third day after surgical correction of acquired heart valve defects, aortocoronary bypass surgery, and left ventricular postinfarction aneurysm resection performed using cardiopulmonary bypass technique. The parameters of the cardio-respiratory system and the value of parameter a in Siggaard-Andersen oxyhemoglobin dissociation curve (ODC) model have been studied. It has been shown that in some patients (about 5%) arterial blood hemoglobin saturation with O2 was lower than the corresponding blood pO2. In respiratory failure, parameter a decreases and the arterial part of ODC is shifted to the left, while in circulatory failure and hypoxia, parameter a of the venous blood increases and the curve is shifted to the right. The corresponding disorders corrected, the shifts are normalized. In severe postoperative complications and critical conditions additional (beside Bohr's effect and 2,3-diphosphoglycerate /2,3-DPG/ impact) ODC shifts, if any, are less marked. A statistically significant and considerable shift in parameter a of arterial ODC segment, as compared to venous one, has been observed. This ODC deviation from the model cannot be accounted for by pH, pCO2 or 2,3-DP impact. It can't be so far excluded that the effect observed might be partially due to regular errors of the measuring devices. However, it might turn out to be a new phenomenon of compensatory ODC shape changes in patients with acute cardiorespiratory disorders.