Evaluation of Lung Ultrasound to Detect Volume Overload in Children Undergoing Dialysis

Background: Ultrasound has been shown to be useful in the evaluation of extravascular lung water in the adult population. Lung ultrasound is used to evaluate a variety of common pediatric pathologies, however there is limited data regarding the use of lung ultrasound among pediatric patients. As such, our study aims to evaluate the utility of ultrasound to evaluate changes in extravascular lung water as represented by b-lines among pediatric patients undergoing hemodialysis.

Methods: This single center prospective observational study included pediatric participants who underwent hemodialysis. After obtaining consent, lung ultrasound examination was used to evaluate b-lines at three time points (a) pre-dialysis, (b) mid-point, and (c) following each dialysis session. Hematocrit was recorded at each timepoint. Pre- and post-dialysis vital signs, weight, and total volume of fluid removed per session were recorded. Continuous variables were summarized with medians and interquartile ranges and categorical variables were summarized with counts and percentages. Reduction in b-lines between study time points was assessed using generalized estimating equations. Repeated measure correlations were used to assess the relationship between the b-lines and the patient’s hematocrit levels.

Results: Six subjects with a total of 26 hemodialysis sessions were included. Of the 26 encounters, nine had 0 b-lines both before and after dialysis. There were no significant reductions among encounters with only 1 or 2 b-lines pre-dialysis. Among encounters with 3 to 5 b-lines pre-dialysis, the number of b-lines reduced by 3.0, a 92.7% reduction from pre- to post-dialysis. Among encounters with at least 6 b-lines prior to dialysis, the number of b-lines reduced by an average of 6 b-lines, equivalent to a 78.8% reduction. One encounter had an increase in b-lines, from 1 to 2.

When considering all sessions, the number of b-line post-dialysis were 2.27 (p < 0.001; 95%CI -3.31, -1.22) lower relative to the number of pre-dialysis b-lines. The number of b-lines were significantly reduced between pre- and mid-dialysis (1.69; p<0.001; -2.58, -0.80), and between mid- and post-dialysis (0.58; p=0.001; 95%CI: -0.90, -0.24).

There was a reduction in average pre- and post-dialysis removed fluid volume: no b-lines (32.0 ml/kg), 1 or 2 b-lines (38.1 ml/kg), 3 to 5 b-lines (44.7 ml/kg), and 6 or more b-lines (45.0 ml/kg).

A significant negative relationship between b-lines and the patient’s hematocrit levels was found for (a) all encounters (r=-0.54; 95% CI: -0.72, -0.34; p<0.001), and for encounters with non-zero b-lines prior to dialysis (r=-0.66; 95% CI: -0.82, -0.42; p<0.001).

Conclusion: The association between reductions in fluid with reductions in b-lines as well as the associations between b-line reduction and hematocrit levels suggest that b-lines reflect changes in volume of pediatric dialysis patients in real time. This may be a valuable method for monitoring fluid status in volume sensitive patient populations.