Influence of ultrafiltration volume on blood volume changes during hemodialysis as observed in day-of-the-week analysis of hemodialysis sessions

Monitoring of relative blood volume changes (Delta RBV) has been propagated for the prevention of hemodialysis hypotension. Although the influence of ultrafiltration volume on Delta RBV is well-known, there is no mention in the literature that Delta RBV results should be interpreted differently for the first, second, or third hemodialysis session of the week. To elucidate whether Delta RBV and its derivative, Delta RBV normalized for ultrafiltration volume (Delta RBV/ultrafiltration ratio), vary systematically over the week, we separately analyzed these parameters for the first, second, and third hemodialysis session of the week in 13 chronic hemodialysis patients over a 17-week period. As expected, mean (+/- SD) ultrafiltration volume was significantly (p <0.001) higher during the first session than during the second and third hemodialysis sessions (3163 +/- 615, 2622 +/- 674 and 2607 +/- 638 ml, respectively). Delta RBV was significantly (p <0.01) more negative at the first session than at the second and third hemodialysis sessions (-10.1 +/- 2.7, -9.3 +/- 3.0 and -9.3 +/- 3.1%, respectively). The Delta RBV/ultrafiltration ratio was significantly (p <0.01) less negative at the first session than at the second and third hemodialysis sessions (-3.2 +/- 0.6, -3.5 +/- 0.8 and -3.6 +/- 0.6%/l, respectively). In conclusion, Delta RBV and the Delta RBV/ ultrafiltration ratio differ systematically between the first and other hemodialysis sessions in patients on a thrice-weekly hemodialysis schedule, most likely as a result of different ultrafiltration volumes.