Can the beneficial effect of Hemocontrol on blood pressure during dialysis be explained by higher blood levels of vasopressin. A pilot study.

Introduction and reason for a study of vasopressin in hemodialysis:
Recently described van der Zee et. al that the plasma vasopressin levels
during hemodialysis hardly increased despite the occurrence of hypovolemia due
to ultrafiltration. They also found in a randomized placebo-controlled trial
that exogenously administered vasopressin during hemodialysis kept the blood
pressure on a higher level than the placebo.
They found that end-stage renal disease (ESRD) had no influence on the
'endogenous removal rate' of plasma vasopressin and vasopressin was not removed
during dialysis. Vasopressin also has a molecular weight> 1000 Da and is not
bound to protein.
In another study with 5 patients the vasopressin levels increased also
significant, but the increase was very modest and significantly less than
healthy individuals show a similar decrease blood volume.

Hemocontrol dialysis is a technique which leads the relative blood volume
change along a preset desired path through continuous adjustment of the
ultrafiltration rate and conductivity of the dialysate. An elevated dialysate
conductivity leads (with some delay) to an increase in plasma sodium levels.
This leads in principle to increase refill through osmosis of fluid from the
interstitial tissue into the bloodstream. The boundaries of the dialysate
conductivity are adjustable - the usual setting is a minimum and maximum
conductance of 135 mmol / l and 160 mmol / l. In practice there is in the 1st
half of the hemodialysis a combination of a high ultrafiltration rate and a
high dialysate conductivity. In the 2nd half of the hemodialysis both the
ultrafiltration rate and dialysate conductivity is lower. Low dialysate
conductiveit in the 2nd half of the dialysis is necessary because the dialysis
patient would otherwise end on a high plasma sodium concentration.

Hemocontrol gives stable dialysis as shown by us and others in
hypotension-prone dialysis patients. It is assumed that the effect of
Hemocontrol is based on a better maintaining (relative) blood volume. However,
we and others found that the finally reached level of relative blood volume
change was not significantly different between - unstable - the standard
dialysis and the - stable - Hemocontrol dialysis. This does not exclude that a
beneficial effect on blood volume Hemocontrol plays a role, for example through
the prevention of sudden short-term decreases in the blood volume. Other
factors may also play a role. In the past some researchers suggested that
dialysis with a higher sodium dialysate has beneficial effects independent of
effects on the blood volume. Thus it is possible that (a part of) the
beneficial effects of vasopressin release during Hemocontrol dialysis are based
on dialysis due to the higher plasma sodium conductance during the 1st half of
the dialysis. In contrast with standard hemodialysis (with constant dialysate
conductivity and ultrafiltration rate) provides dialysis Hemocontrol a 'double
stimulus for vasopressin release, at least in the 1st half of the dialysis, the
hypovolemia (which is during the 1st hours of dialysis is more pronounced than
standard dialysis ) and the higher plasma conductivity during the 1st half of
dialysis compared with standard dialysis.
Would this study (and further research) find that vasopressin plays an
important role, then this knowledge can be used to prevent hypotension during
dialysis.

Based on the hypothesis that hemodialysis with Hemocontol is associated with a
greater and earlier increase in plasma vasopressin levels than standard
dialysis, we examine whether there is a difference in the course of plasma
vasopressin levels between one standard and one HD and one HD Hemocontrol

Twelve patients will be part of this study, undergoing each 2 hemodialysis
treatment , one with a standard hemodialysis (HD) and one with HD Hemocontrol,
a crossover design in randomised order. During both HD treatments we will
repeatedly take blood from the dialysis blood line for the determination of
vasopressin, sodium, urea, glucose and plasma osmolarity. In total 66 cc.

Patients whom are normally treated with standard hemodialysis now get a single
Hemocontrol hemodialysis and vice versa