RELATIVE UNDERESTIMATION OF FLUID REMOVAL DURING HEMODIALYSIS HYPOTENSION MEASURED BY WHOLE-BODY BIOIMPEDANCE

Whole body bioimpedance is considered helpful in monitoring the remova l of excess body water by ultrafiltration in hemodialysis patients. In this study, the cumulative, estimated decrease in extracellular volum e (V-est) modeled from whole body bioimpedance data was compared with measured volume (V-meas) removed by ultrafiltration (UFR = 1.01 +/- 0. 31 L/hr) in 12 patients during 36 high efficiency hemodialysis treatme nts. In the mean, estimated (V-est = 3.0 +/- 1.4 L) and measured volum es (V-meas = 3.4 +/- 1.1 L) correlated linearly: V-est = 1.05 x V-meas - 0.60, r(2) = 0.68. Patients developed hypotension in half the treat ments. Except for a larger decrease in systolic brood pressures in hyp otensive (34 +/- 24 mmHg) vs. stable (14 +/- 15 mmHg) treatments, pati ent and treatment characteristics were not different between groups. H owever, at the end of hemodialysis, the difference V-est - V-meas was -0.8 +/- 0.9 L in hypotensive, and only 0.1 +/- 0.4 L in stable patien ts (p < 0.05). The difference between V-est and V-meas can be explaine d by a predominant removal of excess body water from central body comp artments such as the trunk and the central blood volume during hypoten sion. These compartments are not adequately measured by whole body bio impedance techniques. However, this information could be helpful in id entifying patients with delayed peripheral fluid removal that may occu r when either target weight is too low or UFR rates are too high.