P1068LUNG ULTRASONOGRAPHY IS MORE EFFECTIVE THAN BIOIMPEDENCE OR NT-PRO BNP AT ASSESSING POST-DIALYSIS VOLUME CHANGES
Authors: Teng Hazel , Chua Yan Ting , Wong Weng Kin , Ngoh Lee Ying Clara 
Published: June 2020

Abstract

Background and Aims
At present, there are no precise and quantitative clinical indices for assessing fluid status in haemodialysis (HD). Existing modalities such as plasma B-type natriuretic peptide (NT-pro BNP), measurement of inferior vena cava diameter (IVCD) by ultrasound or bioimpedance spectroscopy (BIS) have limitations and do not always give quantitative measurements to guide dry weight titration. Lung ultrasonography (LUS) has emerged as a novel real-time technique to assess extravascular lung water (EVLW) on HD. Current studies comparing the above techniques often lack standardized dialysis days and timepoints for sampling volume assessment methods. This study aims to compare the performance of LUS against existing methods (NT-pro BNP, IVCD, BIS) of volume assessment in an Asian HD cohort, using a standardised protocol for sampling. The secondary aim was to measure the turnover time required for performing each volume assessment method.

Method
This was a prospective study of 50 chronic HD patients in a single dialysis unit. In this cohort, 34 (68%) had diabetes, and 43 (86%) were on at least 1 antihypertensive. Patients aged more than 21 years, on thrice weekly dialysis with a high flux dialyser for more than 3 months with residual urine output less then 500 ml per day were recruited.
NT-pro BNP, IVCD and BIS were sampled immediately pre- and post- midweek dialysis. 28-intercostal space LUS was performed by a Nephrologist with appropriate certification immediately pre- and 30 minutes after midweek dialysis. EVLW produces lung artefacts (B-lines), which is summated into a B-line score (BLS). We also measured the time required, from performing each volume assessment methodology, to the point of result acquisition.

Results
Pre-HD, lung congestion was classified as mild (BLS ≤ 15) in 6 patients (12%), moderate (BLS 15 – 30) in 12 patients (24%) and severe (BLS &gt; 30) in 32 patients (64%). Median BLS reduced from 46.5 (22.5 – 77.0) pre-HD to 15.5 (9.9 – 21.5) post-HD. There was a linear correlation between changes in BLS and ultrafiltration on HD, with UF 500ml approximately equal to 8.2 B-lines.
There were significant but weak to moderate correlations between pre-HD LUS and BIS (r = 0.457, p = 0.004), IVCD indexed to body surface area during expiration (IVCDimax) (r = 0.371, p = 0.026) and NT-pro BNP (r = 0.406, p = 0.004). Post-HD, correlations between LUS and IVCDimax remained similar (r = 0.353, p = 0.02), but weakened with BIS (r = 0.329, p = 0.021) and became non-significant with NT-pro BNP. This was related to a paradoxical increment in NT-pro BNP and BIS overhydration values post-HD, in up to 40% of the cohort.
Separately, the mean execution time for the various volume measurements were LUS: 6 ± 0.2 minutes, BIS: 5.9 ± 0.4 minutes, IVCD: 4.1 ± 0.3 minutes and the laboratory turnaround time to obtain a NT-pro BNP result was 125 ± 10.6 minutes.

Conclusion
LUS was able to demonstrate a linear correlation with UF volume, and may be more effective then NT-pro BNP or BIS at real-time assessment of fluid changes post-HD. The execution of LUS was no more time-consuming then BIS. LUS is hence likely to be a useful clinical tool for dry weight titration in HD patients.