Assessment Of Ree Via Ventilator Derived VCO2 Indirect Calorimetry In Critically Ill COVID 19 Patients

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TL;DR

This study measured resting energy expenditure (REE) in 20 critically ill COVID-19 patients on mechanical ventilation using ventilator-derived VCO₂ indirect calorimetry. Measured REE (1634±344.4 Kcal/d) was significantly higher than predicted by the Ireton-Jones equation (1062±139.9 Kcal/d) but comparable to ESPEN-recommended nutritional goals of 20 kcal/kg. The findings suggest that ESPEN guidelines are appropriate for this population, while predictive equations like Ireton-Jones are unreliable and indirect calorimetry should be preferred.

Full summary

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**Background:** Critically ill COVID-19 patients experience a hyperinflammatory state that may alter metabolic demands and energy expenditure. Accurate assessment of resting energy expenditure (REE) is essential for appropriate nutritional support, but predictive equations may be unreliable in this population. Indirect calorimetry (IC) is the gold standard for REE measurement, but its feasibility using ventilator-derived VCO₂ measurements in COVID-19 patients had not been well characterized. The study aimed to assess energy requirements of critically ill COVID-19 patients using ventilator-derived VCO₂ indirect calorimetry and compare measured values to both the ESPEN-recommended nutritional goals (20 kcal/kg) and the Ireton-Jones predictive equation.

**Methods:** This was an observational study enrolling critically ill COVID-19 adult patients supported by mechanical ventilation. Indirect calorimetry was performed using ventilator-derived VCO₂ measurements, and REE was calculated using the modified Weir equation (mREE). Each measurement session lasted 8 hours. All patients were clinically stable, sedated, and paralyzed during measurements. Measurements were obtained during the acute phase of the disease (days 3–4 of ICU stay). The measured REE values were compared to nutritional goals recommended by ESPEN (20 kcal/kg) and to REE predicted by the Ireton-Jones equation (pREE). Statistical comparisons were performed to assess differences between measured and predicted values.

**Key Results:** A total of 20 patients were enrolled, of whom 65% were male. The mean age was 64.95±0.9 years, mean BMI was 32.73±4.5, and mean APACHE II score was 19.65±5.38. In 40% of patients, the measurement was performed on day 3 of ICU stay, and in the remaining 60% on day 4. The measured REE (mREE) was 1634±344.4 Kcal/day, corresponding to 20.75±5.41 Kcal/kg of actual body weight (or adjusted body weight if BMI >30). The predicted REE (pREE) using the Ireton-Jones equation was 1062.15±139.9 Kcal/day, or 13.45±1.76 Kcal/kg. There was a statistically significant difference between mREE and pREE (p < 0.001), indicating that the Ireton-Jones equation significantly underestimated energy expenditure. In contrast, mREE and the ESPEN-recommended nutritional goals of 20 kcal/kg were comparable, with no statistically significant difference (p = 0.543).

**Clinical Implications:** This study demonstrates that during the acute phase of COVID-19 critical illness, despite the presence of a significant inflammatory storm, energy requirements remain within the range of ESPEN recommendations (approximately 20 kcal/kg/day). The Ireton-Jones predictive equation was found to be unreliable in this patient population, significantly underestimating true energy expenditure. Ventilator-derived VCO₂ indirect calorimetry offers a more accurate alternative for assessing REE in mechanically ventilated COVID-19 patients. These findings support the use of indirect calorimetry for guiding nutritional therapy in this population and suggest that ESPEN guidelines provide appropriate caloric targets. However, the small sample size (n=20) and single-center design limit generalizability, and larger studies are needed to confirm these findings.