title: Relative blood volume changes underestimate total blood volume changes during hemodialysis.
abstract: BACKGROUND
  Measurements of relative blood volume changes (DeltaRBV) during hemodialysis (HD) are based on hemoconcentration and assume uniform mixing of erythrocytes and plasma throughout the circulation. However, whole-body hematocrit (Ht) is lower than systemic Ht. During HD, a change in the ratio between whole-body to systemic Ht (F cell ratio) is likely to occur as a result of a net shift of low Ht blood from the microcirculation to the macrocirculation. Hence, DeltaRBV may differ significantly from total blood volume changes (DeltaTBV). Therefore, this study compared DeltaRBV and DeltaTBV during HD.
  
  
  METHODS
  Plasma and erythrocyte volumes were measured using (125)I- and (123)I-radioiodinated albumin and (51)Cr-labeled erythrocytes, respectively. After validation of the standardized method in two patients on a nondialysis day, seven patients completed the protocol during HD. (125)I-albumin and (51)Cr-labeled erythrocytes were administered 20 min before the start of HD. (123)I-albumin was administered at 160 min into the HD session to quantify and correct for (125)I-albumin leakage. DeltaRBV was measured continuously throughout HD. The F cell ratio was derived from whole-body and systemic Ht.
  
  
  RESULTS
  Total ultrafiltration volume was 2450 +/- 770 ml. TBV declined from 5905 +/- 824 to 4877 +/- 722 ml during HD. Thus, TBV declined 17.3 +/- 4.4%, whereas the RBV decline was only 8.2 +/- 3.7% (P = 0.001). The F cell ratio increased from 0.896 +/- 0.036 to 0.993 +/- 0.049 during HD (P = 0.002).
  
  
  CONCLUSIONS
  DeltaRBV significantly underestimates DeltaTBV during HD. The rise in F cell ratio strongly suggests that during HD, blood translocates from the microcirculation to the macrocirculation, probably as a cardiovascular compensatory mechanism in response to hypovolemia.
authors: Dialysis Center Groningen, University Medical Center Groningen, Groningen, Netherlands. j.j.dasselaar@dcg.umcg.nl
authors: Judith J
authors: JJ
authors: Dasselaar
authors: Marjolijn N
authors: MN
authors: Lub-de Hooge
authors: Jan
authors: J
authors: Pruim
authors: Hugo
authors: H
authors: Nijnuis
authors: Anneke
authors: A
authors: Wiersum
authors: Paul E
authors: PE
authors: de Jong
authors: Roel M
authors: RM
authors: Huisman
authors: Casper F M
authors: CF
authors: Franssen
mesh_terms: D000368:Aged; D001810:Blood Volume; D006400:Hematocrit; D006403:Hematologic Tests / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D006435:Renal Dialysis