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NDT Advance Access originally published online on January 12, 2006
Nephrology Dialysis Transplantation 2006 21(4):1069-1072; doi:10.1093/ndt/gfk038
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© The Author [2006]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Technical Note

Clamping of the dialysate outlet line in the Genius® dialysis system does not alter dialysate flow or clearances

Wim Van Biesen1, Sunny Eloot2, Annick Verleysen1, Griet Glorieux, Nic Veys1, Raymond Vanholder1 and Norbert Lameire1

1 Renal Division, Department of Internal Medicine, University Hospital Ghent and 2 Department of Hydraulics, University of Ghent, Belgium

Correspondence and offprint requests to: W. Van Biesen, MD, PhD, Renal Division, University Hospital Ghent, De Pintelaan 185, 9000 Ghent, Belgium. Email: wim.vanbiesen{at}ugent.be



   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Discussion
 Conclusion
 References
 
Background. The Genius® dialysis system is advocated as a tool to perform slow extended daily dialysis (SLEDD) in patients with acute renal failure at the intensive care unit. At low blood flows however, it is sometimes problematic to maintain sufficient systemic pressure in the dialysate circuit, a problem that can be overcome by clamping the dialysate outflow line. This intervention can however decrease the flow in the dialysate circuit, and can thus potentially decrease the clearance. This article analyses the impact of this intervention on the blood and dialysate flows and on the removal of retention products.

Methods. The study was done in 20 stable chronic dialysis patients to avoid additional bias caused by changing comorbidities in ICU patients. Patients were treated by Genius®, once with clamping and once without clamping, cross-over in a randomized fashion, and with 1 week interval. Flows in the dialysate and blood circuit were measured with a transsonic flow probe. Urea, creatinine, Beta 2 microglobulin and phosphate were measured in the dialysate, and in the serum before and after dialysis.

Results. There was no clinically significant difference in blood or dialysate flows, nor in clearance or removal of retention products during the sessions with or without clamping.

Conclusions. The technique of using clamping of the dialysate outflow line in the Genius® system to increase systemic pressure, when the system is used in SLEDD, is a safe technique which does not alter the clearances.

Keywords: Genius®; continuous renal replacement therapy; intensive care unit; hemodialysis



   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Discussion
 Conclusion
 References
 
The Genius® system consists of single-batch setup with a closed dialysate circuit and a glass reservoir containing 90 l of dialysate [1]. Due to differences in physico-chemical properties of spent and fresh dialysate, and the specific architecture of the system (Figure 1), there is no recirculation of spent dialysate [2]. The Genius® system is easy to handle as basically only one parameter is monitored: the systemic pressure in the dialysate reservoir. This pressure is generated by the hydraulic pressure in the blood compartment of the dialyser, causing a flux of water to the dialysate compartment. As the reservoir is a closed system, the system pressure rises, and this pressure is measured at the ultrafiltration line. All the changes in blood, dialysate or ultrafiltration flow inevitably result in a change in system pressure, and thus an alarm. In this way, a bad arterial blood flow, or a venous obstruction or deconnection, can be detected in less than 1 s, making the machine safe to use. With a high-flux membrane, it is easier to maintain higher systemic pressures, but the system can also be run with low-flux membranes. In the latter case however, it is difficult to maintain systemic pressure if ultrafiltration is also necessary, as this decreases systemic pressure.


Figure 1
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  		Fig. 1. Schematic representation of the Genius® system. 1: occlusive blood and dialysate pump; 2: air bubble detector; 3: artificial kidney (high flux); 4: venous expansion chamber; 5: system pressure monitor; 6: occlusive ultrafiltration rate pump; 7: ultrafiltrate receptacle; 8: fresh dialysate; 9: separation line spent–fresh dialysate; 10: spent dialysate; 11: UV irradation lamp; 12: glass container wall; X: place of clamping of dialysate outflow line.

 
The Genius® concept is becoming more and more recommended as an alternative dialysis modality for continuous renal replacement therapy (CRRT) and intermittent haemodialysis (IHD) in patients with acute renal failure in the intensive care unit [3,4]. More specifically, besides the practical advantage of its mobility, the ease of use of citrate as anticoagulant [5] and the low cost, the Genius® system is well designed to allow the implementation of slow extended daily dialysis (SLEDD) [6,7]. In this concept, dialysis intensity is modified by adapting the blood and dialysate flow to the haemodynamic and metabolic stability of the patients. The SLEDD therapy combines the advantages of CRRT (slow ultrafiltration, smooth clearance) with those of IHD (adaptable blood and dialysate speed, economy, ease of use). The Genius® system has some specific features which make it very suitable for SLEDD. There is no need for a water treatment unit in the ICU, and dialysis can be performed at all locations in the hospital. The system is easy to handle, and avoids the need for industrially prepared dialysate or substitution fluids [8]. Due to the slow cooling of the dialysate, the patient is always in a zero thermodynamic balance, which adds to the haemodynamic stability. In addition, in the Genius® system, the dialysate flow and blood flow are always equal, as they are generated by the same pump. A blood flow of 150 ml/min, for example, is always accompanied by a dialysate flow of 150 ml/min, and in this setup, the system will be able to perform for 10 h without any need to replace the dialysate reservoir. An alternative option is to use the 2:1 reduction set, whereby dialysate flow is only 50% of the blood flow [9]. The extended dialysis time also allows to use low ultrafiltration rates. However, in practice, the use of such low blood flows does not generate sufficient system pressure, which causes the machine to go into alarm status and discontinue the treatment. This technical problem can be overcome by clamping the dialysate outlet line (Figure 1) with a specific adjustable screw, which increases systemic pressure without disabling the alarm for other causes of pressure alterations. In theory, this technique could however result in a decrease of dialysate flow, and thus in a reduced efficiency of the treatment.

This study was performed to analyse the impact of clamping of the dialysate outflow line on the dialysate and blood flows in the system and on the adequacy of the therapy.



   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Discussion
 Conclusion
 References
 
The study has been undertaken in chronic dialysis patients to avoid interfering factors of bias related to the instability of acute dialysis patients. All chronic dialysis patients treated with Genius® at a satellite unit of the University Hospital Ghent were included. All these patients were clinically stable, with a regular diet and without intercurrent acute disease at the moment of the experiments. All patients gave informed consent according to the protocol approved by the local ethical committee. Measurements were perfomed on the mid-week dialysis day. There was a randomization of clamping vs non-clamping as the first treatment. There was 1 week separation between the different test settings.

Flows were measured with an ultrasound clamp-on flow probe (Transsonic Systems, Inc., Ithaca, NY). Results were measured before calibration of the probes to avoid reader bias. The coefficient of variation of the probes is less than 1% according to the specifications of the manufacturer. All readings were done in quadriplucate, and the mean value was retained. Flow probes were calibrated afterwards in the lab by gravimetrical water flow measurements, and the actual flow values were calculated. Flows were measured at the closest point to the arterial and venous access, and at the dialysate outflow line, i.e. the line bringing fresh dialysate to the artificial kidney. Flow measurements were performed under 4 different conditions: blood flow of 350 and 150 ml/min, each with and without clamping of the dialysate outflow line. During clamping of the dialysate line, the clamp was adjusted to obtain a constant systemic pressure of 300–320 mmHg. This was done to have the same target for all patients, and to test the system at its extremes. Clamping was performed with a specifically designed screw (Fresenius Medical Care, Bad Homburg, Germany). Dialysis was performed for 240 min, using a FX60 membrane (polysulfone high flux, Fresenius Medical Care, Bad Homburg, Germany). Ultrafiltration rate was identical under both conditions (clamped vs unclamped) in each patient. However, ultrafiltration rate was adapted to the individual patient's ultrafiltration needs.

Retention products (phosphor, Beta 2 microglobulin, urea and creatinine) were measured in the serum before and after dialysis (after 4 min of blood pump speed at 50 ml/min), and in the ultrafiltrate in a single batch. The ultrafiltrate sample was obtained after thorough shaking and stirring of the ultrafiltration recipient. Paired t-test was used to compare results of treatments with and without clamping.



   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Discussion
 Conclusion
 References
 
Twenty patients were included after giving informed consent, 8 males, 9 diabetics, mean age 67±7 years. Results for the flow measurements are given in Table 1. The systemic pressure was 144±23 mmHg at a blood speed of 350 ml/min without clamping. In the experiments with clamping, the systemic pressure was per protocol aimed at more than 300 mmHg. Clamping resulted in a decrease of venous blood flow (149±9 vs 142±10 ml/min, P = 0.006) and dialysate flow (127±5 vs 120±14 ml/min, P = 0.02) when the pump speed was at 150 ml/min. All other variables were comparable with and without clamping.


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  		Table 1. Flow measurements

 
The results for the removal and clearances are given in Table 2. There was no clinically significant difference in total amount of any of the retention products removed during the dialysis session, clearance or reduction rate between treatments with and without clamping.


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  		Table 2. Clearance studies

 


   Discussion
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
Conclusion
 References
 
The Genius® dialysis concept has some specific properties that make it a valuable tool to perform SLEDD in an intensive care setting [6]. A good separation of spent and fresh dialysate [2], microbiological safety [10] and adequacy [11] of this concept have been demonstrated before.

This study demonstrates that clamping of the dialysate outlet line in the Genius® system to increase the system pressure when using low blood flows is a safe method that does not alter the clearance, neither of small molecules like urea or creatinine, or of larger molecules, like Beta 2 microglobulin or phosphate. This is an important observation, as at the low blood flows used during SLEDD, clamping of the dialysate outlet line is often necessary to increase the system pressure. Although dialysate flow was statistically speaking lower after clamping, this difference has no clinically relevant meaning, as it is less than 5%, and it did not result in a decreased removal of retention products. Clamping will prohibit frequent alarms because of low system pressure, and in this way avoids repetitive cessation of therapy. As the alarm is triggered by relative changes of pressure within a predefined fixed fork of 40 mmHg, independent of the absolute pressure value, this intervention does not interfere with the safety of the alarm.

Intriguingly, there was a difference between the arterial and venous blood flow as measured and that indicated by the blood pump speed. This difference was not noted for the dialysate flows. There are several potential explanations for this observation. First, the semi-occlusive mechanism of the rotating pump might result in small deviations of flow through deformation of the tubing when a strong negative suction has to be provided. This strong negative suction is of course more pronounced in the blood compartment than in the dialysate compartment. This hypothesis is also compatible with the observation that the deviations are less pronounced with slower blood flows, where also the negative pressure is less pronounced. A second hypothesis might be that the calibration of the flow probe was done with reverse osmosis water in a Genius® tubing. The viscosity and density of reverse osmosis water is however different from that of blood. This does not affect the study results, as all measurements were performed with the patient as his own control. This hypothesis does not explain why the deviations were far less pronounced at lower blood flows.

Although in this setting, clamping did not influence flows or clearance, it has to be stated that these experiments were performed in stable chronic patients.



   Conclusion
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 Conclusion
References
 
This small and adjustable technical intervention increases the ease of use of the SLEDD technique with the Genius® system, without jeopardizing clearance or safety.

Conflict of interest statement. None declared.



   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 Conclusion
 References
 

  1. Fassbinder W. Renaissance of the batch method? Nephrol Dial Transplant 1998; 13: 3010–3012[Free Full Text]
  2. Dhondt AW, Vanholder RC, De Smet RV et al. Studies on dialysate mixing in the Genius single-pass batch system for hemodialysis therapy. Kidney Int 2003; 63: 1540–1547[CrossRef][Medline]
  3. Fassbinder W. Experience with the GENIUS hemodialysis system. Kidney Blood Press Res 2003; 26: 96–99[Medline]
  4. Lonnemann G, Floege J, Kliem V, Brunkhorst R, Koch KM. Extended daily veno-venous high-flux haemodialysis in patients with acute renal failure and multiple organ dysfunction syndrome using a single path batch dialysis system. Nephrol Dial Transplant 2000; 15: 1189–1193[Abstract/Free Full Text]
  5. Morgera S, Scholle C, Melzer C et al. A simple, safe and effective citrate anticoagulation protocol for the genius dialysis system in acute renal failure. Nephron Clin Pract 2004; 98: c35–c40[CrossRef][Web of Science][Medline]
  6. Vanholder R, Van Biesen W, Lameire N. What is the renal replacement method of first choice for intensive care patients? J Am Soc Nephrol 2001; 12 [Suppl 17]: S40–S43
  7. Lameire N, Van Biesen W, Vanholder R. Dialysing the patient with acute renal failure in the ICU: the emperor's clothes? Nephrol Dial Transplant 1999; 14: 2570–2573[Free Full Text]
  8. Van Biesen W, Lameire N. SLEDD and hybrid renal replacement therapies for acute renal failure in the ICU. J.L Vincent. Yearbook of Intensive Care and Emergency Medicine 2003; 663–678
  9. Kielstein JT, Kretschmer U, Ernst T et al. Efficacy and cardiovascular tolerability of extended dialysis in critically ill patients: a randomized controlled study. Am J Kidney Dis 2004; 43: 342–349[CrossRef][Web of Science][Medline]
  10. Lonnemann G, Dumann H, Schmidt-Gurtler H. Improved dialysate quality and decreased cytokine levels in ESRD patients treated with the Genius hemodialysis system. Nieren und hochdruckkrankheiten 1997; 26: 479
  11. Fliser D. Renal replacement therapy in the intensive care unit with a single-pass batch system. EDTNA ERCA J 2002; [Suppl 2]: 8[Medline]
Received for publication: 10. 9.05
Accepted in revised form: 11.12.05


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