Use of the Body Composition Monitor for Fluid Status Measurements in Subjects with High Body Mass Index.

Background: Fluid management is a central aspect of haemodialysis (HD). Body composition monitor (BCM)-measured overhydration (OH) can improve fluid management strategies, but there remains uncertainty about its use in subjects with high body mass index (BMI). This study explored whether the observed tendency for HD patients with high BMI to complete dialysis fluid depleted according to BCM is associated with an artefact in the BCM models, or with systematic differences in the prescription and delivery of treatment.

Methods: To isolate the effect of BMI from effects relating to treatment, BCM measurements were made on 20 healthy subjects with high BMI. Mean OH was compared with a previously reported cohort of healthy subjects with normal BMI. To further explore BCM-measured OH in HD patients, measurements were made pre- and post-dialysis on 10 patients with high BMI alongside relative blood volume monitoring. Body shape was classified to assess associations between shape and OH.

Results: The mean OH for healthy subjects with high BMI was -0.1 litres, which was not different from that of healthy subjects with normal BMI. Median BCM-measured OH for HD patients was 1.8 and -1.8 litres pre- and post-dialysis respectively, while blood volume and blood pressure were maintained. Body shape correlated with OH in control subjects but not HD patients.

Conclusions: We found no evidence of systematic bias in BCM-measured OH with high BMI in healthy subjects. BCM-measured post-dialysis fluid depletion in asymptomatic patients with high BMI appears to result from greater tolerance of ultrafiltration and ability to maintain blood volume.