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

Objective: Using a system, which accuracy is equivalent to the gold standard Douglas Bag (DB) technique for measuring oxygen consumption (VO 2 ), carbon dioxide generation (VCO 2 ), 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. VO 2 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 VO 2 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 VO 2 than the critical care patients ( p <0.01). The post-surgery patients also had higher VCO 2 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 VO 2 , VCO 2 , and RQ. Critical care patients may have less activity in metabolism represented by lower values of VO 2 and VCO 2, which were less variable over time as compared to those of post-cardiothoracic surgery patients.