P142
FLUID STATUS MEASUREMENTS BY BIOIMPEDANCE IN EXTREMES OF BODY
COMPOSITION
David Keane 1,2 , Kim Bowra 3 , Paul Chamney 6 , Stefanie Heinke 6 , Kathryn Kearney 3 , Sameer
Limaye 4 , Elizabeth Lindley 1,2 , Stephen Pollard 5
Departments of 1 Renal Medicine, 2 Medical Physics, 3 Dietetics and Nutrition, 4 Elderly Care,
5 Surgery, Leeds Teaching Hospitals NHS Trust and 6 Fresenius Medical Care
INTRODUCTION: Poor fluid management is a significant component of the elevated cardiovascular risk observed in haemodialysis (HD) patients. Bioimpedance spectroscopy measurements by the Body Composition Monitor (BCM, Fresenius Medical Care) provide an objective assessment of fluid status which has been shown to improve fluid management and outcomes (Onofriescu et al, AJKD 2014). Routine use of BCM in a large unit over several years indicates that post-dialysis, HD patients with low BMI are more likely to remain over-hydrated, whereas patients with high BMI can tolerate extreme dehydration (Lindley & Keane, J Ren
Nursing 2014). We aimed to investigate this systematic difference between HD patients at the extremes of body composition.
METHODS: BCM measurements were made pre- and post-dialysis on 5 HD patients classified as malnourished by specialist dietetic assessment, and 10 HD patients with BMI greater than 30.
The time averaged fluid overload (TAFO) was calculated with data from a single session and compared against a value of 0.5 L, which represents the median TAFO from a large patient population (Moissl et al, CJASN 2013). Measurements were repeated at one month for repeatability.For comparison, BCM measurements were also made on 20 malnourished subjects and 20 subjects with BMI greater than 30 who had normal renal function. Malnutrition was defined as a Malnutrition Universal Scoring Tool (MUST) score greater than 2. The distribution of hydration at both extremes of body composition was compared with the expected distribution for normally hydrated subjects.To assess the effect of limb shape in the high BMI groups, subjects were assigned a categorical shape factor based on visual assessment of the change in cross sectional area from thigh to ankle, and from upper arm to wrist. For HD patients, refilling of the intravascular volume from the tissues was categorised as adequate or insufficient based on intradialytic blood volume monitoring (BVM).Comparisons between groups were made using Student’s-t, Kruskal-Wallis or Mann-Whitney tests as appropriate.
RESULTS: For the HD group, malnourished patients had a median overhydration (OH) of 2.5
L pre-dialysis and 1.8 L post-dialysis, giving a TAFO of + 2.2 L. Those with high BMI had a slightly lower median OH of 1.8 L pre-dialysis and were dehydrated by a median of -1.8 L postdialysis, giving a TAFO of 0.0 L. BVM results suggested that those patients finishing dialysis dehydrated (up to 3.3 L) maintained adequate refilling. Repeat measures at one month showed consistent results.For those with normal renal function, the malnourished subjects had a mean
OH of 1.3 L (95% CI: 0.8 to 1.8, p <.0001) while those with high BMI were normally hydrated
(mean OH= -0.1 L; 95% CI: -0.9 to 0.7; p=.6). For the high BMI group, there was an association between subjects showing greater changes in cross sectional area along the length of the limb and lower values of OH (p=.004).
CONCLUSIONS: Some fluid retention, as measured by BCM, seems to be normal in malnourished subjects regardless of renal function. The dehydration observed in HD patients with high BMI was not found in BMI-matched subjects with normal renal function. Tolerance of dehydration induced by ultrafiltration may be mediated by a ‘buffering’ effect from the extracellular fluid in the increased adipose tissue compartment. Further research into intravascular refilling could facilitate development of appropriate fluid management strategies for these patients.