Indirect calorimetry measurement of energy expenditure related to body position changes in healthy adults

Early mobilization is advocated to prevent intensive care unit-acquired physical weakness, but the patient's workload and its changes in response to body position changes have not been established. We used indirect calorimetry to determine the energy expenditure (EE) in response to body position changes, and we assessed EE's correlation with respiratory parameters in healthy volunteers: 8 males and 8 females, mean age 23.4±1.3 years. The subjects started in the resting supine position followed by a 30° head-up position, a 60° head-up position, an upright sitting position, a standing position, and the resting supine position. EE was determined in real time by indirect calorimetry monitoring the subject's respiratory rate, tidal volume (VT), and minute volume (MV). The highest values were observed immediately after the subjects transitioned from standing to supine, and this was significantly higher compared to the original supine position (1,450±285 vs. 2,004±519 kcal/day, p<0.01). Moderate correlations were observed between VT and EE (r=0.609, p<0.001) and between MV and EE (r=0.576, p<0.001). Increasing VT or MV indicates an increasing patient workload during mobilization. Monitoring these parameters may contribute to safe rehabilitation. Further studies should assess EE in critically ill patients.