A practical method to assess myocardial oxygen consumption (MVO2) would be a valuable adjunct to monitoring critically ill patients. Previously we reported a step-down in O2 saturation from atrial to pulmonary artery blood (Delta SO2), likely to result from mixing atrial with coronary sinus blood. We hypothesize that Delta SO2 bears a direct relationship to coronary sinus blood O2 saturation and by extension, to myocardial O2 consumption (MVO2).
An equation was developed using a two-compartment mass transport model relating MVO2 to DeltaSO2. The model was tested using data obtained from 45 patients with pulmonary artery (PA) catheters inserted during their stay in the ICU. We computed Delta SO2 from blood samples drawn from the proximal and distal ports of the PA catheter as Delta SO2 = (SO2)proximal- (SO2)distal.
As shown in Figure 1, our model predicts a linear relationship between Delta SO2 and MVO2 (P < 0.0001; R2 = 0.76).
There appears to be a robust linear relationship between Delta SO2 and MVO2.
Further studies comparing calculated and direct measures of MVO2 are needed prior to advocating the use of Delta SO2 as an estimate of myocardial energy metabolism in critically ill patients.
G. Gutierrez, None.