DETERMINATION OF CIRCULATING BLOOD-VOLUME BY CONTINUOUSLY MONITORING HEMATOCRIT DURING HEMODIALYSIS

Dialysis-induced hypovolemia occurs because the rate of extracorporeal ultrafiltration exceeds the rate of refilling of the blood compartmen t. The purpose of this study was to evaluate a method for calculating circulating blood volume (BV) during hemodialysis (HD) from changes in hematocrit (Hct) shortly (2 to 10 min) before and after ultrafiltrati on (UF) was abruptly stopped. Hct was monitored continuously during 93 HD treatment sessions in 16 patients by an optical technique and at s elected times by centrifugation of blood samples. Total plasma protein and albumin concentrations were also measured at selected times. Cont inuously monitored Hct correlated with Hct determined by centrifugatio n (R = 0.89, N = 579). Relative changes in BV determined by continuous ly monitored Hct were not different from those determined by total pla sma protein concentration (P = 0.05; N = 273). Calculated BV at the st art of dialysis (4.1 +/- 1.3 L) was not different (P = 0.18, N = 12) f rom that derived anthropometrically from the patient's dry weight (4.6 +/- 0.8 L), and calculated BV when UF was stopped was 3.2 +/- 0.5 L ( 46 +/- 7 ml/kg body wt). These tatter estimates of BV are consistent w ith those determined previously by dilution techniques in HD patients. It was concluded that (1) relative changes in BV assessed by continuo usly monitored Hct were unbiased and (2) BV can be determined noninvas ively during HD by continuously monitoring Hct and temporarily stoppin g UF.