Changes in the mixed venous blood oxygen saturation during the acute phase of myocardial infarction and administration of dobutamine.

Clinical significance of the continuous monitoring of mixed venous oxygen saturation (SvO2) by Catheter Oxymetry System was evaluated in 45 patients with acute myocardial infarction (AMI). Patients with AMI were classified into 4 groups according to Forrester's hemodynamic classification. The mean SvO2 value for each group was 70.4 +/- 4.1% for subset I, 54.7 +/- 6.9% for subset II, 55.8 +/- 9.8 for subset III, and 47.0 +/- 8.0% for subset IV. Subsets II, III, and IV showed significantly low values compared to subset I (p less than 0.01). The relationship between PCW and SvO2 level was expressed by the negative regression line y = -0.8x + 73.8 (r = -0.64, p less than 0.01). The curve representing the relationship between CI and SvO2 level was expressed by the equation y = 53.8 logx + 42.7 (r = 0.68, p less than 0.01). The SvO2 level of the 14 patients who showed a significantly low value of 56.9 +/- 8.2% before administration of 5 micrograms/kg/min dobutamin, increased to a mean value of 66.8 +/- 7.9%, as well as the CI after 60 min. However, PCW demonstrated no pronounced changes because of dobutamine administration. Since the SvO2 level highly correlated to the cardiac pumping function in acute phase of myocardial infarction, polygraphic monitoring of SvO2 was found to be a useful index for evaluating changes in the hemodynamics. It was also a very useful measure in evaluating the effects of dobutamin.