The effect of arteriovenous fistulae in haemodialysis patients on whole body and segmental bioelectrical impedance

BACKGROUND: Bioelectrical impedance (BIA) is a potentially useful methodfor measuring body water and soft-tissue composition in patients withchronic renal failure. The majority of whole body impedance is derived fromthe limbs with only a small contribution from the trunk, and thusabnormalities of the limbs could have an exaggerated effect on estimates oftotal body impedance. METHODS: This study investigated the effect ofarteriovenous fistulae in the arm in haemodialysis patients on bodycomposition measurement by whole body BIA. Body composition estimates frommeasurements on fistula and non-fistula sides of the body were compared andsegmental impedance measurements of the arms were also performed. RESULTS:Whole body resistance was markedly lower on the fistula side of the bodycompared with the nonfistula side at 517.1 (124.3) omega compared with561.5 (121.2) omega, P < 0.0005. This difference was accounted for bydifferences in the arm segments. This was attributed to swelling of thefistula arm which had a greater mid- arm circumference at 28.5 (2.1) cmcompared with the contralateral side at 27.5 (2.0) cm, P < 0.05. Thisresulted in greater estimates for total body water from the fistula side at38.6 (10.0) kg compared with 36.6 (8.6) kg from the non-fistula side, P< 0.05 and fat-free mass at 51.1 (11.8) kg from the fistula sidecompared with 49.1 (11.2) kg from the non-fistula side, P < 0.005.Estimates of body fat from the fistula side, 13.1 (6.9) kg, were less thanthe nonfistula side, 15.0 (6.0), P < 0.005. CONCLUSIONS: The presence ofarteriovenous fistulae for vascular access in haemodialysis patients mayhave a significant effect on estimates of body composition by BIA.