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.