The usefulness of a new indirect calorimeter in critically ill adult patients.

Background & Aims: The use of indirect calorimetry to determine energy requirements is highly recommended in critically ill patients. To facilitate this a new and easy to use calorimeter (Q-NRG+, Cosmed) was developed. The primary aim of our study was to describe the usefulness of this calorimeter and, secondarily, to investigate the agreement between measured and predicted energy needs in a large cohort of critically ill adult patients.

Methods: A prospective observational study was conducted among adult mechanically ventilated patients with COVID-19. Indirect calorimetry (Q-NRG+) to measure resting energy expenditure (mREE) was performed in the first week after admission and, wherever possible, repeated weekly. Reasons for not performing indirect calorimetry were reported. Parameters of indirect calorimetry and patient's conditions during the measurements were collected. Measurements were defined as valid if less than 10% overall variation in VO and VCO and respiratory quotient ranges between 0.67 and 1.1 were observed. mREE was compared with predictive REE (pREE) using standard formulas to explore hypo (<90%)-and hypermetabolism. (>110%). Bland-Altman method and two-way mixed intraclass correlation coefficients (ICC) (single measures) were used to assess the agreement between mREE and pREE.

Results: Indirect calorimetric measurements were performed in 180 of the 432 admitted patients (42%). Of the 276 performed measurements 85% were valid, and of these 90% were used to tailor nutritional therapy. Most patients were male (71%), median age was 62 years [IQR 52; 70]. Logistical issues (absence of measuring staff, no device, no stock of disposables, MRSA isolation) and clinical issues (e.g Fio>70%, detubated but still in ICU) were the main reasons for not performing indirect calorimetry. The majority of the REE-measurements indicated either hypo- or hypermetabolism (57% week 1 and 56% week 2). The correlation between mREE and pREE was very moderate (ICC = 0.527).

Conclusions: Although indirect calorimetry was performed in less than half of the patients, it proved to be of value to guide nutritional therapy. We conclude that the technique is easily applicable and expect that its impact can be significantly increased with the resolution of logistical and organizational issues.