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

Abstract

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 healthy volunteers and 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 hrs and 15 minutes 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. Generalized linear mixed-effect model identified that the post-surgery patients had higher VO2 than the critical care patients (p<0.01). The post-surgery patients also had higher VCO2 than critical care patients (p<0.01). There were no significant differences in RQ between the two groups. 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 lower values of VO2 and VCO2, which were less variable over time as compared to those of post-cardiothoracic surgery patients.