Indirect Calorimetry in Critically Ill Patients With COVID-19: More Questions Than Answers.

Yu et al describe the resting energy expenditure in critically ill patients with coronavirus disease 2019 (COVID‐19), and all patients were under mechanical ventilation and sedated.

Physiological variables are not provided; nevertheless, one can assume that as the patients were in the critical care unit, multiorgan failures could have been present. It will be interesting to know critical condition scores to give an idea about the multisystem compromise and to extrapolate the hypermetabolism described to other COVID‐19 critical care units.

Respiratory quotients (RQs) are not provided, and information about the metabolic state is lacking. Information about feeding regimens or fed state, sedative drugs, and muscular relaxants would be important as main resting energy expenditure determinants.

Calculating RQs carbon dioxide production (VCO2)/oxygen consumption (VO2), I underscore the results (Table 1) as follows: RQ is 0.7 in 3 patients, which means (at last theoretically) that metabolically the patients were in a fasting state with consequent ketogenesis and gluconeogenesis, , , , , or else one would speculate that if sedative drugs received are mainly based in propofol, low RQ is the reflection of its exclusively lipid content oxidation. Just 1 patient has an RQ suggestive of mixed‐substrate oxidation (0.82). ,

Table 1

Respiratory quotients (RQs) calculations per each patient

	VCO2 (mL/min)	VO2 (mL/min)	RQ
Patient 1	582	750	0.776
Patient 2	303	416	0.728
Patient 3	295	455	0.648
Patient 4	452	585	0.773
Patient 5	468	565	0.828
Patient 6	401	642	0.625
Patient 7	555	798	0.695
Mean (SD)	437 (112)	602 (141)	0.725 (0.073)

RQ, respiratory quotient; VCO2, carbon dioxide production; VO2, oxygen consumption.

Noticeably, 3 patients had RQs <0.7, with 2 patients´ values extremely outside of physiologic human RQs (patients 6 and 7). In physiologic conditions, the lowest RQ derived from lipid oxidation is 0.707, and the lowest RQ possible in humans is 0.67 from ethanol oxidation. , There is not a clear explication for such low RQ values in the population analyzed by Yu et al.

MClave et al described RQ limitations to truly reflect substrate oxidation, but in the clinical condition described by Yu et al, with extremely low RQs 0.62 and 0.64 (the lowest from the RQ expected by fasting), one would wonder about indirect calorimetry device calibration errors or the presence of technical conditions that can alter indirect calorimetry results, such as air leaks, hypoventilation, or the use of β‐blockers.

The knowledge provided by Yu et al opens the opportunity to explore the fine metabolic conditions of critically ill patients with COVID‐19, which are still widely unknown, and offers the basis for the generation of interesting metabolic hypotheses, such as supra physiological VO2 and VCO2 that need to be explored.