DIAMETER OF INFERIOR CAVAL VEIN (VCD) AND BIOELECTRICAL-IMPEDANCE ANALYSIS (BIA) FOR THE ANALYSIS OF HYDRATION STATUS IN PATIENTS ON HEMODIALYSIS

Background: Vena cava diameter (VCD) measurement is an accepted method to evaluate hydration status in patients on hemodialysis. Bioelectric al impedance analysis (BIA) is a less laborious method to assess hydra tion variables and more suitable for routine patient care. However, BI A has not yet been validated in dialysis patients. We investigated whe ther BIA can replace VCD in patients on hemodialysis. Methods: In 20 s table hemodialysis patients [age (+/- SD): 47 +/- 17 yrs, dialysis dur ation (+/- SD): 76 +/- 59 months] hydration status was evaluated by VC D. Impedance variables such as resistance, reactance and phase angle w ere provided by BIA. They were used to calculate intracellular water ( ICW), extracellular water (ECW) and total body water (TBW). Results: V CD did not correlate with TBW-BIA, but correlated with ECW/TBW (r = 0. 46; p < 0.025), ECW/m(2) (r = 0.42; p < 0.005) and ICW/ECW (r = -0.49; p < 0.005). Hemodialysis decreased TBW with 2.7 +/- 1.91. The differe nce in ECW before and after dialysis (8.9 +/- 1.3 and 7.1 +/- 1.41, re spectively) was significant (p = 0.001). The same did not hold true fo r ICW(13.3 +/- 1.4 and 13.1 +/- 1.41). Major underhydration (n = 9; VC D <6.5 mm/m(2)) revealed sharp limits for ICW/ECW (>1.80) and ECW/TBW (< 0.35), whereas these BIA-variables were significantly (p < 0.005) d ifferent from those in minor underhydration (n = 8; 6.6 < VCD < 8.0 mm /m(2)), normohydration (n = 15; 8 < VCD <11.5 mm/m(2)) and overhydrati on (n = 7; VCD >11.5 mm/m(2)). Conclusion: BIA can replace VCD only in major underhydration (VCD <6.5 mm/m(2)). Fluid loss during hemodialys is is caused by a decrease of ECW, compatible with the postulation tha t excess fluid volume is carried by the extracellular compartment.