[Assessment of real myocardial energy demand using indirect calorimetry in early postoperative period after cardiac surgery].

Objective: To evaluate actual myocardial energy requirements using indirect calorimetry, oxygen delivery (DO), oxygen extraction ratio (OER), 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, VO and DO, 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, VOI and VCO significantly increased by 10%, DOI increased by 27%, and OER 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. VOI 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 VO and DO with moderate decrease of OER in postoperative period. VO 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.