OBJECTIVE

To evaluate actual myocardial energy requirements using indirect calorimetry, oxygen delivery (DO₂), oxygen extraction ratio (O₂ER), cardiac output (CO) and their components, as well as to study the impact of positive inotropic agent (dobutamine) on myocardial metabolism in early postoperative period after cardiac surgery.

MATERIAL AND METHODS

We measured the main metabolic parameters using indirect calorimetry in 20 patients after on-pump cardiac surgery with cardioplegia. To evaluate the impact of metabolic load on CO, VO₂ and DO₂, we administered dobutamine 3 µg/kg/min at the second phase of the study. Basal metabolic parameters were recorded together with CO and arterial and venous blood gas composition.

RESULTS

Under dobutamine infusion, VO₂I and VCO₂ significantly increased by 10%, DO₂I increased by 27%, and O₂ER decreased by 10%. Aerobic metabolism increased from 1902.3±380.6 to 2130.9±423.1 kcal/day. The predicted energy expenditure values (Harris-Benedict equation) were significantly lower (1759.7±255.6 kcal/day). Cardiac index increased by 26%, stroke volume — by 10%, heart rate — by 21%. Central venous pressure, left ventricular end-diastolic volume and ejection fraction were the same. VO₂I obtained through indirect calorimetry were higher than those measured using the reverse Fick method. At the first phase, these values were 138.6±28.9 and 72.8±27.6 ml/min/m², at the second phase — 155.4±28.2 and 68.1±27.1 ml/min/m², respectively.

CONCLUSION

Energy expenditure exceeded the predicted values. This was accompanied by elevated VO₂ and DO₂ with moderate decrease of O₂ER in postoperative period. VO₂ values assessed by indirect calorimetry and reverse Fick method represent two distinct physiological parameters, and they are not interchangeable. Further studies are required to assess this technology in critically ill patients.