| Abstract [eng] |
Patients in critical condition can exhibit changes in fluid distribution and muscle wasting. Bioelectrical impedance analysis is a convenient tool for assessing body composition, but fluid fluctuations can distort derived body composition indices. Ultrasound examination of muscles provide more accurate monitoring of muscle dynamics. Aim.To evaluate changes in bioelectrical impedance analysis parameters in the critically ill, apply fluid overload corrections, and compare uncorrected and corrected body composition parameters with actual fluid balance and muscle ultrasound data. Objectives.1.To evaluate changes in actual fluid balance and bioelectrical impedance analysis hydration indices at 1, 5, and 7 days. 2.To evaluate changes in muscle thickness measured by ultrasound at 1, 5, and 7 days. 3.To determine the relationship between fluid excess calculated based on bioelectrical impedance analysis and actual fluid balance.4. To compare the correlation between changes in unadjusted and adjusted lean body mass and changes in muscle thickness determined by ultrasound. Methods. A secondary analysis of prospectively collected data was performed in a mixed intensive care unit. 143 patients were included. Bioelectrical impedance analysis and muscle ultrasound were performed on days 1, 5, 7. Actual fluid balance was calculated based on documented fluid intake and output. Fluid overload determined by bioelectrical impedance was calculated based on the assumption that the excess accumulates mostly in the extracellular compartment. Lean mass indices were calculated as unadjusted, bioelectrical impedance-adjusted, and actual balance-adjusted values. Descriptive and repeated measures analysis and correlation assessment were applied. Results.In the first week, the dynamics of fluid overload were observed: fluid excess increased until day 5 and decreased between days 5 and 7; this trajectory was observed both based on actual fluid balance (median 1.51L day 5 and 0.99L day 7) and based on fluid excess calculated by bioelectrical impedance (median 1.79kg day 1, 1.96kg day 5, and 1.86kg day 7). Both methods yielded similar values (difference of −0.26kg day 5 and −0.33kg day 7), and a moderate correlation was found between them (ρ=0.536 day 5 and ρ=0.449 day 7; p < 0.0001). Muscle thickness measured by ultrasound decreased consistently (median:11.77cm→11.31cm→10.56cm), whereas unadjusted lean body mass increased on day 5 and decreased on day 7 (63.9kg→65.3kg→63.4kg). After adjusting for fluid overload, the initial increase diminished: bioelectrical impedance-adjusted lean body mass remained higher on day 5 but decreased on day 7 (61.82kg→63.40kg→60.62kg), whereas lean mass adjusted for actual fluid balance began to decrease as early as day 5 (62.2kg→60.55kg), better reflecting the downward trend observed by ultrasound. Analysis of linear mixed models showed that both the muscle thickness measured by ultrasound and the lean body mass adjusted for actual fluid balance decreased statistically significantly over time. Meanwhile, unadjusted and bioelectrical impedance-adjusted lean mass did not show a decreasing trend. Conclusions.During the first week, a biphasic fluid overload pattern was observed (an increase until day 5, followed by a decrease), which was equally reflected in both the actual fluid balance and the fluid excess indices calculated based on bioelectrical impedance, with a moderate correlation observed between them. Ultrasound revealed a consistent decrease in muscle thickness, whereas uncorrected lean body mass in the early period was influenced by fluid status and did not reflect true muscle dynamics. Fluid correction altered the interpretation of lean body mass: correction based on bioelectrical impedance only reduced the early increase, whereas correction based on actual fluid balance revealed a consistent decrease corresponding to muscle wasting observed by ultrasound. |
