RELATIONSHIP BETWEEN OXYGEN-UPTAKE AND MIXED VENOUS OXYGEN-SATURATIONIN THE IMMEDIATE POSTOPERATIVE PERIOD

Background: During muscular exercise, a negative correlation has been demonstrated between the value of mixed venous oxygen saturation (S (v ) over bar(O2)) and the level of muscular work, expressed at each leve l as the ratio of oxygen uptake (V-O2) to each subject's maximal oxyge n uptake (V(O2)max). Because the immediate postoperative period is ass ociated with an increase in whole body oxygen demand, and in this rega rd resembles the effects of muscular exercise, a similar correlation m ay exist during this period. Methods: V(O2)max was determined in 11 pa tients 3-5 days before coronary artery bypass surgery. During the firs t 2 postoperative h, V-O2 and S (v) over bar(O2) were monitored. V-O2 was measured by indirect calorimetry and S (v) over bar(O2) by a fiber optic pulmonary arterial catheter. Results: The highest postoperative value of V-O2 was most often associated with visible shivering and ran ged among patients from 19% to 53% of preoperatively measured V(O2)max . There was a highly significant negative correlation between S (v) ov er bar(O2) and the ratio V-O2/V(O2)max. This correlation was observed when data were examined collectively (136 simultaneous determinations of the two variables) and at the individual level (10-18 determination s for each patient). The slopes and the y intercepts of individual lin es of correlation were within a narrow range. Conclusions: During the first 2 postoperative h after coronary artery bypass surgery, V-O2 rar ely exceeds 50% of preoperative V(O2)max. Assuming a stable state of m yocardial function, S (v) over bar(O2) measurement may provide an indi rect means of assessment of the ''exercise test'' imposed on patients recovering from general anesthesia.