INFLUENCE OF HYDRATION STATE ON PLASMA-VOLUME CHANGES DURING ULTRAFILTRATION

To assess the influence of hydration state on plasma volume (PV) changes during ultrafiltration, 11 clinically normhydrated patients on maintenance hemodialysis were studied intraindividually during 2 hydration states differing by 2-15% of lean body mass (LBM). Plasma volume was measured continually during a 15-min ultrafiltration test including an ultrafiltration of 1% of target weight and during a 45-min follow-up period of blood recirculation through the dialyzer without ultrafiltration. In all patients a maximal decrease in relative PV was more pronounced when there was less hydration and when the grade of hydration correlated inversely with the maximal response of PV decrease (r = -0.68, p < 0.001). The same was observed between the hydration state and the slope of the PV decrease (r = -0.69, p < 0.001). Plasma refilling was estimated in the period following ultrafiltration. The slope of the plasma volume increase correlated with the grade of hydration (r = 0.31, p < 0.05) as did the asymtote of PV (r = 0.4, p < 0.01), It is concluded that the less hydrated a dialysis patient is, the more pronounced will be the fall of the ultrafiltration-induced plasma volume and the less distinct will be the recovery of the plasma volume after the discontinuation of ultrafiltration.