Continuous and repeat metabolic measurements compared between post-cardiothoracic surgery and critical care patients

Abstract

Objective: Using a system, which accuracy is equivalent to the gold standard Douglas Bag (DB) technique for measuring oxygen consumption (VO₂), carbon dioxide generation (VCO₂), and respiratory quotient (RQ), we aimed to continuously measure these metabolic indicators and compare the values between post-cardiothoracic surgery and critical care patients.

Methods: This was a prospective, observational study conducted at a suburban, quaternary care teaching hospital. Age 18 years or older patients who underwent mechanical ventilation were enrolled.

Results: We included 4 post-surgery and 6 critical care patients. Of those, 3 critical care patients died. The longest measurement reached to 12 h and 15 min and 50 cycles of repeat measurements were performed. VO₂ of the post-surgery patients were 234 ± 14, 262 ± 27, 212 ± 16, and 192 ± 20 mL/min, and those of critical care patients were 122 ± 20, 189 ± 9, 191 ± 7, 191 ± 24, 212 ± 12, and 135 ± 21 mL/min, respectively. The value of VO₂ was more variable in the post-surgery patients and the range of each patient was 44, 126, 71, and 67, respectively. SOFA scores were higher in non-survivors and there were negative correlations of RQ with SOFA.

Conclusions: We developed an accurate system that enables continuous and repeat measurements of VO₂, VCO₂, and RQ. Critical care patients may have less activity in metabolism represented by less variable values of VO₂ and VCO₂ over time as compared to those of post-cardiothoracic surgery patients. Additionally, an alteration of these values may mean a systemic distinction of the metabolism of critically ill patients.

Keywords: Carbon dioxide generation; Douglas bag; Indirect calorimetry; Oxygen consumption; Respiratory quotient.