Should relative blood volume changes be routinely measured during the dialysis session?

Abstract Relative blood volume (RBV) monitoring is frequently used in haemodialysis patients to help guide fluid management and improve cardiovascular stability. RBV changes are typically estimated based on online measurements of certain haemoconcentration markers, such as haematocrit (HCT), haemoglobin (HGB) or total blood protein concentration (TBP). The beginning of a haemodialysis procedure, i.e. filling the extracorporeal circuit with the patient’s blood (with the priming saline being infused to the patient or discarded) may be associated with relatively dynamic changes in the circulation, and hence the observed RBV changes may depend on the exact moment of starting the measurements. The aim of this study was to use a mathematical model to assess this issue quantitatively. The model-based simulations indicate that when the priming saline is not discarded but infused to the patient, a few-minute difference in the moment of starting RBV tracking through measurements of HCT, HGB or TBP may substantially affect the RBV changes observed throughout the dialysis session, especially with large priming volumes. A possible overestimation of the actual RBV changes is the highest when the measurements are started within a couple of minutes after the infusion of priming saline is completed.

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Effect of controlled extracorporeal blood cooling on ultrafiltration-induced blood volume changes during hemodialysis.

Journal of the American Society of Nephrology ◽

10.1681/asn.v86956 ◽

1997 ◽

Vol 8 (6) ◽

pp. 956-964 ◽

Cited By ~ 1

Author(s):

D Schneditz ◽

K Martin ◽

M Krämer ◽

T Kenner ◽

F Skrabal

Keyword(s):

Heat Flux ◽

Blood Volume ◽

Volume Changes ◽

Hemodynamic Stability ◽

Fluid Removal ◽

Arterial Blood ◽

Group A ◽

Blood Pressures ◽

Group B ◽

Relative Blood Volume

Considerable amounts of heat may be lost or gained through the extracorporeal circuit during hemodialysis and influence the hemodynamic stability of the dialysis patient. The effects of two levels of extracorporeal heat flux (Jtherm in W) on blood pressures and ultrafiltration-induced blood volume changes were studied in eight patients on conventional hemodialysis. Treatments were controlled automatically for mild to medium Jtherm of either -13.4 +/- 3.3 W (group A) or -30.2 +/- 3.7 W (group B) (1 W = 1 J/s = 3.6 kJ/h = 0.239 cal/s = 0.86 kcal/h) and repeated once. Values are given as mean +/- SD. With low blood flows (Qb = 251 +/- 21 ml/min), dialysate temperatures were automatically set at 37.3 +/- 0.3 degrees C (group A) and 35.3 +/- 0.2 degrees C (group B) for the two levels of Jtherm, respectively. Arterial blood temperatures increased by 0.4 +/- 0.4 degree C with mild extracorporeal cooling (group A), whereas arterial blood temperatures slightly decreased by -0.1 +/- 0.4 degree C in the group with medium negative heat flux (group B) (P < 0.01). Blood pressures tended to drop in the warm dialysate group and to remain unchanged in the cool dialysate group (P = NS). Relative blood volume changes calculated from on-line ultrasonic blood measurements were significantly larger with cool (-12.8 +/- 8.3 vol%) than with warm (-7.2 +/- 5.5 vol%, P < 0.05) dialysate, indicating reduced fluid removal from peripheral body compartments during cool hemodialysis ultrafiltration. Despite the larger reduction in intravascular volume, intradialytic hemodynamic stability was maintained with extracorporeal cooling and cool dialysate prescription.

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FC 095INCREASED VASCULAR REFILLING BY FEEDBACK-CONTROLLED ULTRAFILTRATION PROFILE

Nephrology Dialysis Transplantation ◽

10.1093/ndt/gfab128.003 ◽

2021 ◽

Vol 36 (Supplement_1) ◽

Author(s):

Susanne Kron ◽

Til Leimbach ◽

Joachim Kron

Keyword(s):

Clinical Practice ◽

Blood Volume ◽

Venous Blood ◽

Control Program ◽

Wilcoxon Test ◽

Dialysis Session ◽

Bolus Administration ◽

Before And After ◽

On Line ◽

Relative Blood Volume

Abstract Background and Aims Refilling volume has not been a measurable parameter in clinical practice so far, as knowing the absolute blood volume (BV) is a prerequisite. Recently, we developed a method to determine absolute BV, thus enabling quantification and comparison of the refilling volume under various conditions. In this study, we evaluated refilling with a constant UF rate and with a feedback-controlled UF profile. Method Forty dialysis patients were included and studied during their routine dialysis sessions. Absolute BV was determined by indicator dilution. Immediately at the beginning of the dialysis session (before UF was started), an on-line infusate bolus of 240 mL was injected into the venous blood line by pressing a button on the keypad of the dialysis machine 5008 (FMC). The resulting increase in relative blood volume before and after bolus administration (RBVpost-RBVpre) was used to calculate absolute BV: absolute BV (in mL) = bolus volume (240 mL) x 100 / increase in RBV (in %) Absolute BV at the end of dialysis was calculated as: absolute BVend = absolute BVbeginning x RBVend in % / 100 Refilling volume was calculated as: refilling volume = UF volume – (absolute BV beginning – absolute BV end) The refilling fraction is given as: Refilling fraction = refilling volume / UF volume UF was either set as constant UF rate or as UF profile. In contrast to the constant UF rate, the UF program integrated in the dialysis machine 5008 initially starts with twice the average UF rate. If half of the prescribed UF target is reached, the control program keeps UF and refilling in balance. Results Refilling data of 40 dialysis sessions with constant UF were compared to 40 sessions with the feedback-controlled UF profile. Refilling volumes were 1.72 ± 0.76 l during the profiled sessions and 1.60 ± 0.64 l in sessions with constant UF rate (p < 0.001, Wilcoxon test). UF volumes were similar in both treatments (2.20 ± 0.90 and 2.26 ± 0.81 L, respectively). There was a strong correlation between refilling volume and UF volume in both treatments (r = 0.98 with profile, and r = 0.92 with constant UF rate, respectively). The refilling fraction was significantly higher (p < 0.001, t-test) with the feedback-controlled UF profile (77.2 ± 8.5%) than with a constant UF rate (70.4 ± 9.9%). In one patient there was a higher refilling fraction with constant UF rate (p < 0.0001). Symptomatic hypotension occurred in 3 patients, all in sessions with constant UF rate. Refilling was not lower in these 3 cases. Conclusion Refilling volume predominantly depended on UF volume. The refilling was improved by a high UF rate at the beginning of dialysis. This confirms previous data that initially high UF rates induce the refilling sooner, and, therefore, the refilling volume is higher with the same UF. An increased UF rate at the beginning can improve volume management in haemodialysis patients. With a UF profile, more volume can be removed while maintaining a stable absolute BV which may prevent hypotension in some cases. We therefore recommend that such UF profiles should be used more often in routine clinical practice. However, with every litre of UF volume, BV is reduced by more than 200 ml, at a constant UF rate even by approximately 300 ml. This must be taken into account when prescribing the UF volume.

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