Relative blood volume measurements during hemodialysis

From NIER

by Dr. Judith J. Dasselaar and Dr. Casper F.M. Franssen

University Medical Center Groningen, Groningen, The Netherlands.

Originally published as general introduction to the PhD thesis of Dr. Judith J. Dasselaar, which she published in September 2007 under supervision of her promotor Prof. dr. Paul E. de Jong and co-promotores Dr. Casper F.M. Franssen and Dr. Roel M. Huisman at the University Medical Center Groningen in The Netherlands.

Contents 1 Abstract 2 Hemodialysis 3 Dialysis hypotension 3.1 Blood volume during hemodialysis 3.2 Compensatory mechanisms 4 Relative blood volume 4.1 Biofeedback 4.2 Blood volume tracking 5 References

[edit] Abstract

In the following paragraphs a brief pathophysiological overview is provided concerning the most frequently occurring complication during a hemodialysis treatment: dialysis hypotension. In addition, in light of the continuing and ongoing efforts made to prevent dialysis hypotension an introduction into the measurement of relative blood volume is given.

[edit] Hemodialysis

In 1943 the first human hemodialysis treatment was performed by Willem J. Kolff in Kampen, the Netherlands [1]. During the following decades the applicability of dialysis evolved from a life-saving procedure for acute renal failure patients to a life-sustaining long term therapy for patients with chronic renal failure [2]. To date there are approximately 5300 individuals in the Netherlands that require dialysis treatment. Seventy-five percent of these patients receive hemodialysis while the remainder is treated with peritoneal dialysis [3].

[edit] Dialysis hypotension

One of the most frequent complications during hemodialysis is dialysis hypotension. It occurs in an estimated 20 % of all hemodialysis sessions [4]. The symptoms vary from fatigue, yawning, cramps, nausea and vomiting to angina pectoris or loss of consciousness. The symptoms are generally transitory. However, dialysis hypotension can also cause permanent damage, such as a myocardial infarction, a cerebrovascular accident, intestinal infarction or an occlusion of the arterio-venous fistula [5,6]. Moreover, dialysis hypotension has a number of other negative consequences. It may lead to chronic overhydration of the cardiovascular system due to an inability to reach ‘dry weight’. Dialysis hypotension may also lead to underdialysis. This is because patients with symptoms of low blood pressure are regularly disconnected from dialysis earlier, so that the actual duration of dialysis is often shorter than desirable for an adequate Kt/V [4,5]. In addition, there are indications that the transfer of waste products from certain tissues to the blood is decreased during hypotension due to the decreased perfusion of these tissues [7].

There are multiple causes for dialysis hypotension. However, two factors play a crucial role:

1. The decrease in blood volume during hemodialysis.
2. The incapacity of the cardiovascular system to respond adequately to this decrease in blood volume. What are involved here are the so-called cardiovascular compensatory mechanisms. The purpose of these compensatory mechanisms is to maintain the blood pressure at a normal level in situations in which the circulating blood volume has decreased.

[edit] Blood volume during hemodialysis

Most hemodialysis patients produce little or no urine and, therefore, the excess fluid that is accumulated between dialysis sessions must mainly be removed during dialysis. Most of the excess fluid is located in the interstitial tissue. During hemodialysis, fluid is withdrawn from the circulation in the artificial kidney. In the meantime, the excess fluid moves from the interstitial tissue into the circulation. The rate at which the fluid is withdrawn from the circulation (the ultrafiltration rate) is almost always higher than the rate at which the fluid moves from the interstitial tissue into the circulation (the plasma refilling rate or refill rate). In other words, the refill rate lags behind the ultrafiltration rate. As a result of the difference between the refill rate and the ultrafiltration rate, the blood volume will drop during every hemodialysis session in which fluid is withdrawn.

[edit] Compensatory mechanisms

The purpose of the compensatory mechanisms is to maintain the blood pressure at a normal level in situations in which the circulating blood volume is decreased. The three most important cardiovascular compensatory mechanisms are: venous constriction, an increase in the pulse rate and contractile force of the heart, and constriction of the arterioles in certain organs [4].

[edit] Relative blood volume

Since the decrease in blood volume during hemodialysis is an important factor in the etiology of dialysis hypotension, it follows that the preservation of blood volume during hemodialysis is an important target in the prevention of intra-dialytic hypotension. Therefore, devices that continuously and non-invasively monitor relative blood volume changes (∆RBV) during hemodialysis have been developed over the past decades [8-10].

∆RBV can be calculated from changes in the concentration of certain intra-vascular constituents, e.g. hemoglobin [11-13]. In principle, the concentration of intra-vascular constituents that are too large to be dialysed increases during hemodialysis when fluid is withdrawn from the circulation. The change in blood volume in comparison with the blood volume at the start of hemodialysis is calculated by means of the following formula [12,14]:

Blood volume change (in %) = ((Intra-vascular constituentstart hemodialysis / Intra-vascular constituentduring hemodialysis) – 1) x 100.

[edit] Biofeedback

Some small studies have shown that adapting the ultrafiltration rate based on observed ∆RBV, has a positive effect in diminishing intra-dialytic hypotension [8,15,16]. Alternatively, automatic biofeedback systems have been developed that alter certain treatment parameters in response to ∆RBV. The goal of these ∆RBV based biofeedback systems is to prevent a severe or abrupt decease in blood volume in order to prevent the development of dialysis hypotension. One of these systems is based on the concept of blood volume tracking (BVT) (Hemocontrol, Gambro-Hospal, Lyon, France) [17].

[edit] Blood volume tracking

The BVT system guides the measured ∆RBV during hemodialysis along a pre-programmed so-called ideal blood volume trajectory by continuously adjusting the dialysate sodium concentration and ultrafiltration rate. The ideal blood volume trajectory is based on an individual value for the ratio ‘∆RBV normalized for ultrafiltration volume (∆RBV/UF)’ which is determined on the basis of a number of hemodialysis sessions in which ∆RBV is monitored in relation to the changes in the patients condition and blood pressure.

The BVT system has three targets during hemodialysis:
1) keeping the ∆RBV above the allowed ∆RBV in relation to the total ultrafiltration volume,
2) achieving the prescribed ultrafiltration volume, and
3) achieving a pre-set equivalent conductivity in order to avoid a sodium overload.

The BVT system adjusts the ultrafiltration rate and dialysate sodium concentration throughout the hemodialysis session. At the start of the session the maximum ultrafiltration rate is 1.8 times the average ultrafiltration rate and the dialysate conductivity initially rises to the maximum allowed conductivity (usually 16.0 mS/cm). As the RBV starts to decline at a steeper angle than the ∆RBV trajectory allows, the ultrafiltration rate will decrease and dialysate sodium concentration will remain high. When RBV rises, the ultrafiltration rate will increase while the dialysate sodium concentration decreases. The hemodialysis machine will indicate when one of the three targets, or the 3 combined, deviates too much from the targets.

Several publications have demonstrated that hemodialysis with BVT leads to a decrease in the frequency and/or the severity of hemodialysis hypotension [17-23].

[edit] References

1.	Kolff WJ. De Kunstmatige Nier (The Artificial Kidney), Thesis, University of Groningen, The Netherlands, 1946.
2.	Kloppenburg WD. Adequacy and Nutrition in Chronic Hemodialysis, Thesis, University of Groningen, The Netherlands, 2002.
3.	Registratie Nierfunctievervanging Nederland. Statistisch verslag 2005. Stichting Renine, Rotterdam, Nederland, 2005.
4.	Daugirdas JT. Pathophysiology of dialysis hypotension: an update. Am J Kidney Dis 38: S11-S17, 2001.
5.	Schreiber MJ, Jr. Clinical dilemmas in dialysis: Managing the hypotensive patient. Setting the stage. Am J Kidney Dis 38: S1-S10, 2001.
6.	John AS, Tuerff SD, Kerstein MD. Nonocclusive mesenteric infarction in hemodialysis patients. J Am Coll Surg 190: 84-88, 2000.
7.	Ronco C, Brendolan A, Milan M, Rodeghiero MP, Zanella M, La Greca G. Impact of biofeedback-induced cardiovascular stability on hemodialysis tolerance and efficiency. Kidney Int 58: 800-808, 2000.
8.	Steuer RR, Leypoldt JK, Cheung AK, Senekjian HO, Conis JM. Reducing symptoms during hemodialysis by continuously monitoring the hematocrit. Am J Kidney Dis 27: 525-532, 1996.
9.	Basile C. Should relative blood volume changes be routinely measured during the dialysis session? Nephrol Dial Transplant 16: 10-12, 2001.
10.	de Vries JP, Donker AJ, de Vries PM. Prevention of hypovolemia-induced hypotension during hemodialysis by means of an optical reflection method. Int J Artif Organs 17: 209-214, 1994.
11.	Paolini F, Mancini E, Bosetto A, Santoro A. Hemoscan: a dialysis machine-integrated blood volume monitor. Int J Artif Organs 18: 487-494, 1995.
12.	Steuer R, Harris D, Conis J. A new optical technique for monitoring hematocrit and circulating blood volume: its application in renal dialysis. Dial Transplant 22: 260-265, 1993.
13.	Mancini E, Santoro A, Spongano M, Paolini F, Rossi M, Zucchelli P. Continuous on-line optical absorbance recording of blood volume changes during hemodialysis. Artif Organs 17: 691-694, 1993.
14.	Santoro A, Mancini E, Paolini F, Zucchelli P. Blood volume monitoring and control. Nephrol Dial Transplant 11: 42-47, 1996.
15.	Stiller S, Wirtz D, Waterbar F, Gladziwa U, Dakshinamurty KV, Mann H. Less symptomatic hypotension using blood volume controlled ultrafiltration. ASAIO Trans 37: M139-M141, 1991.
16.	Ishihara T, Igarashi I, Kitano T, Shinzato T, Maeda K. Continuous hematocrit monitoring method in an extracorporeal circulation system and its application for automatic control of blood volume during artificial kidney treatment. Artif Organs 17: 708-716, 1993.
17.	Santoro A, Mancini E, Paolini F, Spongano M, Zucchelli P. Automatic control of blood volume trends during hemodialysis. ASAIO J 40: M419-M422, 1994.
18.	Mancini E, Santoro A, Spongano M, Paolini F, Zucchelli P. Effects of automatic blood volume control over intradialytic hemodynamic stability. Int J Artif Organs 18: 495-498, 1995.
19.	Santoro A, Mancini E, Paolini F, Cavicchioli G, Bosetto A, Zucchelli P. Blood volume regulation during hemodialysis. Am J Kidney Dis 32: 739-748, 1998.
20.	Basile C, Giordano R, Vernaglione L, Montanaro A, De Maio P, De Padova F, Marangi AL, Di Marco L, Santese D, Semeraro A, Ligorio VA. Efficacy and safety of haemodialysis treatment with the Hemocontrol biofeedback system: a prospective medium-term study. Nephrol Dial Transplant 16: 328-334, 2001.
21.	Santoro A, Mancini E, Basile C, Amoroso L, Di Giulio S, Usberti M, Colasanti G, Verzetti G, Rocco A, Imbasciati E, Panzetta G, Bolzani R, Grandi F, Polacchini M. Blood volume controlled hemodialysis in hypotension-prone patients: a randomized, multicenter controlled trial. Kidney Int 62: 1034-1045, 2002.
22.	Begin V, Deziel C, Madore F. Biofeedback regulation of ultrafiltration and dialysate conductivity for the prevention of hypotension during hemodialysis. ASAIO J 48: 312-315, 2002.
23.	Wolkotte C, Hassell DR, Moret K, Gerlag PG, van den Wall Bake AW, van der Sande FM, Kooman JP. Blood volume control by biofeedback and dialysis-induced symptomatology. Nephron 92: 605-609, 2002.