Respiratory quotient and resting energy expenditure: Correlation with sonographic muscle wasting in nutritional evaluation of critically ill patients.

BACKGROUND

Indirect calorimetry (IC) is the gold standard for determining energy requirements in critically ill patients. Muscle ultrasound quantifies morphological changes in skeletal muscle, offering a rapid and accessible method for nutritional assessment.

OBJECTIVE

To explore the relationship between respiratory quotient (RQ), resting energy expenditure (REE) obtained via IC, and sonographic muscle wasting in critically ill patients at a Mexican tertiary care hospital.

METHODS

In this descriptive, longitudinal, prospective study, 49 ICU patients aged ≥18 years, hemodynamically stable, under invasive mechanical ventilation and sedoanalgesia, were enrolled. Ultrasound measurements of quadriceps muscle thickness were performed at ICU admission (day 0) and on day 3. These were correlated with REE and metabolic balance derived from IC.

RESULTS

The mean age was 55.7 ± 15.1 years, 20 female patients (40.8 %) and 29 male patients (59.2 %). On day 0, both latero-lateral (r = 0.368, p = 0.009) and anteroposterior (r = 0.461, p = 0.009) diameters correlated moderately with REE. By day 3, only the anteroposterior diameter retained correlation (r = 0.320, p = 0.025). Muscle wasting did not correlate directly with REE, but ROC analysis identified an 11 % cut-off for muscle loss predictive of metabolic balance, with an AUC of 0.765 (95 % CI: 0.559-0.972), sensitivity of 0.714, and specificity of 0.429.

CONCLUSIONS

Sonographic measurement of quadriceps thickness correlates with REE at ICU admission, but only the anteroposterior diameter remains reliable by day 3. Identifying patients with <11 % muscle loss on day 3 may indicate metabolic balance, which is crucial for improving outcomes in critically ill patients.