Relation between mixed venous blood oxygen saturation and cardiac pumping function at the acute phase of myocardial infarction.

Abstract

In this study, we monitored changes in the mixed venous blood oxygen saturation (Sv-O2) level of 45 patients with acute myocardial infarction and compared these results to the traditional parameters. The Sv-O2 level was found to correlate well with the clinical course of patients and their hemodynamic conditions. The mean Sv-O2 level of the group having congestive heart failure (53.3 +/- 8.4%) was found to be statistically lower than those without (69.8 +/- 5.6). Furthermore, patients whose Sv-O2 level was lower than 60% were found to be at greater risk for heart failure and a very high mortality rate. Patients were classified into four subsets according to Forrester's hemodynamic classification; their Sv-O2 levels were 70.7 +/- 4.1% (I: 23 cases), 54.7 +/- 6.9% (II: 8 cases), 55.8 +/- 9.4% (III: 10 cases), and 47.0 +/- 8.0 (IV: 4 cases), respectively. A severe relationship between pulmonary capillary wedge pressure and Sv-O2 having a correlation coefficient of r = -0.64 was observed, and a logarithmic curvilinear relation between cardiac index approximately Sv-O2, stroke volume index approximately Sv-O2 and left ventricular stroke work index approximately Sv-O2 was also evident. When the decrease in the Sv-O2 level was more than 5%, it always showed a significant decrease in the cardiac index. This study suggested tht continuous monitoring of the Sv-O2 level revealed simultaneous changes in the hemodynamic state, which lead to the assistance and aid for treating patients with critical conditions of acute myocardial infarction. In such circumstances, it was noted that the Sv-O2 level should be maintained above 60% in order to stabilize the hemodynamic state.