Comparison of fat‐free mass adjusted for overhydration obtained by bioelectrical impedance and computed tomography in critically ill patients with COVID‐19: A secondary analysis of a prospective cohort

Background Muscle mass is a strong predictor of clinical outcomes. However, its continuous monitoring is not always feasible in critically ill patients. Surrogate methods, such as bioelectrical impedance analysis (BIA), may be affected by overhydration (OH). The aim of this study was to evaluate the agreement of BIA‐derived fat‐free mass (FFM) adjusted for hydration status in comparison with muscle mass assessed by computed tomography (CT) in critically ill patients with pneumonia due to COVID 19. Methods This secondary analysis includes patients with a CT scan of the third lumbar vertebra (L3) and a BIA performed within the first 24 to 48 h of hospital admission. FFM and hydration status were estimated using BIA (FFM BIA ), and then adjusted to OH (FFM OH ). Images from the skeletal muscle area obtained from L3 were used to calculate the FFM derived from CT (FFM CT ). The concordance between FFM derived from CT and BIA was analyzed using Bland‐Altman and Student t test. Results Seventy‐four patients were included. FFM BIA overestimated compared with CT (54.6 ± 10.3 kg vs 47.4 ± 10.9 kg) with a mean difference of 7.2 kg (limits of agreement, −5.1 to 19.5; P < 0.01). Overestimation decreased by FFM OH , with a mean difference of 3.5 kg (limits of agreement, −9.6 to 16.8; P = 0.06). Conclusion FFM OH assessed by BIA shows a better agreement with FFM CT in comparison with FFM BIA .