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Arteriovenous fistula recirculation in hemodialysis

Arteriovenous fistula recirculation in hemodialysis
Literature review current through: Jan 2024.
This topic last updated: Jan 04, 2024.

INTRODUCTION — Hemodialysis access recirculation is an important cause of inadequate dialysis delivery to individual patients. It is important to diagnose recirculation in order to optimize dialysis delivery. In addition, screening for recirculation may be used as a surveillance technique for the early detection of fistula stenosis, the correction of which may prevent thrombosis.

This topic reviews hemodialysis access recirculation. Other causes of decreased dialysis delivery are discussed elsewhere. (See "Prescribing and assessing adequate hemodialysis".)

Other methods of surveillance of fistulas and grafts to prevent thrombosis are discussed elsewhere. (See "Clinical monitoring and surveillance of the mature hemodialysis arteriovenous fistula" and "Clinical monitoring and surveillance of hemodialysis arteriovenous grafts to prevent thrombosis".)

DEFINITION AND MECHANISM — Hemodialysis access recirculation occurs when dialyzed blood returning through the venous needle re-enters the extracorporeal circuit through the arterial needle, rather than returning to the systemic circulation (figure 1).

The re-entry of dialyzed blood into the extracorporeal circuit reduces solute concentration gradients across the dialysis membrane by mixing already dialyzed blood with undialyzed blood. Such mixing reduces the efficiency of dialysis. Significant recirculation can lead to a discrepancy between the amount of hemodialysis prescribed (prescribed Kt/V urea) and the amount of hemodialysis delivered (delivered Kt/V urea). (See "Prescribing and assessing adequate hemodialysis", section on 'Causes of inadequate dialysis'.)

The degree of access recirculation for any dialyzed solute can be calculated from the following formula:

 Percent recirculation   =   ([P  -  A]  ÷  [P  -  V])  x  100

where P, A, and V refer to the concentration of solute in the peripheral (systemic) blood, predialyzer arterial line, and postdialyzer venous circuit, respectively.

If there is no recirculation, solute concentration in the peripheral (systemic; P) is equal to that in the blood entering the access (A), and the above formula has a value of 0. On the other hand, access recirculation exists whenever solute concentration in the arterial line blood is lower than that in the peripheral sample, indicating re-entry of dialyzed blood into the arterial line.

CAUSES — Access recirculation is caused by low access blood flow. If access blood flow is less than the prescribed pump flow (typically 400 to 500 mL/min), backflow from the venous limb of the access is necessary to support the extracorporeal blood flow rate set by the blood pump. Low access blood flow may be due to venous stenosis, intra-access stenosis, or arterial inflow stenosis [1].

Recirculation does not result from placing needles too closely together as long as access blood flow exceeds the machine blood flow rate. However, substantial recirculation (20 percent or more) is caused by reversed needle placement [2].

INDICATIONS FOR MEASURING RECIRCULATION — The major indication to measure recirculation in patients with either a fistula or graft is that the delivered Kt/V is below target despite prescribing an adequate hemodialysis prescription. (See "Prescribing and assessing adequate hemodialysis".)

Recirculation is a common cause of inadequate dialysis delivery. In one study of 146 stable dialysis patients in whom measurements of Kt/V and access recirculation were obtained every month for three successive months, 25 percent of low Kt/V values resulted from significant access recirculation [3].

The presence of significant recirculation is an indication for radiographic evaluation of the fistula since recirculation is a marker for stenosis. Stenosis can usually be corrected by an intervention. Correcting the stenosis usually increases the efficiency of dialysis and often achieves the target Kt/V without changing the dialysis prescription. Most well-functioning fistulas will have no recirculation. Thus, a recirculation value between 5 and 10 percent should prompt radiographic evaluation, depending on the method used to measure recirculation. (See 'Non-urea-based indicator dilutional methods' below and 'Urea-based methods' below.)

Monitoring recirculation may also be used as a surveillance method of screening for fistula (but not graft) stenosis among patients who have no evidence of inadequate delivered Kt/V [4]. However, we agree with the 2006 National Kidney Foundation/Dialysis Outcomes Quality Initiative (NKF/DOQI or KDOQI) that recirculation is not the optimal method of surveillance for fistula stenosis and, if used as such, should only have a minor role [5]. Significant recirculation tends to be a late marker of stenosis, which limits its utility. Other methods of screening for fistula stenosis, such as measurement of access flow, are preferred. These methods are discussed elsewhere. (See "Clinical monitoring and surveillance of the mature hemodialysis arteriovenous fistula", section on 'Rationale for monitoring and surveillance of AV fistulas'.)

Recirculation should not be used as a surveillance tool to screen for stenosis in grafts, since other methods, such as monitoring access flow, are far more sensitive [6]. This is because, unlike fistulas, grafts are often thrombosed by the time access blood flow is low enough to cause recirculation. Fistulas, on the other hand, may remain patent at much lower access flow rates.

METHODS OF MEASURING RECIRCULATION — Methods of measuring recirculation include:

Non-urea-based indicator dilutional methods

Urea-based methods, using either a two- or three-needle approach

The preferred methods are non-urea-based dilutional methods. Urea-based methods are not optimal, because there are errors inherent in urea measurement that prevent accurate determination of recirculation. The difficulties in determining recirculation using urea-based methods are discussed below. (See 'Urea-based methods' below.)

Non-urea-based methods require special equipment. If such equipment is not available, a urea-based method may be used, providing a two-needle stopped or slowed-flow recirculation approach is used rather than the more traditional three-needle approach. This is consistent with the 2006 Kidney Disease Outcomes Quality Initiative (KDOQI) recommendations [5].

Non-urea-based indicator dilutional methods — Indicator dilutional methods utilize inline monitoring of an exogenous substance that is injected into the venous outflow line. Arterial sensors measure a component of blood that is affected by the diluent. The most commonly used detection methods include the following:

Ultrasound velocity dilution

Thermal dilution

Optical dilution

Conductivity dilution

Potassium dilution

Threshold recirculation values for the non-urea-based methods have not been established. However, access recirculation in fistulas with high access flow rates should be near 0 percent. A recirculation value above 5 to 10 percent by a non-urea-based method should prompt fistulography. Some clinicians use a 5 percent threshold, whereas others use a 10 percent threshold for non-urea-based methods [5].

Individual methods are discussed below:

Ultrasound velocity dilution – For this method, two ultrasound sensors are attached to venous and arterial lines. Ultrasound velocity (determined by protein concentration of blood) is detected by the venous and arterial sensors and transduced by an attached monitor. The ultrasound signal (velocity) changes when blood is diluted by saline. A bolus of saline is introduced into the venous line, and the arterial and venous sensors detect the resulting dilution of blood. The ratio of dilution in the venous and arterial lines provides the percentage of access recirculation.

Thermal dilution – Thermal dilution requires inline temperature sensors that are integrated into some dialysis machines and monitor the blood temperature in the arterial and venous lines. The system is automated. A bolus of blood that is cooled by decreasing the dialysis fluid temperature is introduced into the venous line and monitored by the venous line temperature sensor. Recirculation is determined from changes in temperature detected by the temperature sensor on the arterial line.

Optical dilution – This method utilizes an optical sensor (Crit-Line monitor) that is situated at the arterial inflow port of the dialyzer. This sensor detects changes in the optical density of blood in response to a saline bolus injected into the venous line.

Conductivity dilution – Arterial and venous sensors detect changes in blood conductivity in response to an injected bolus of hypertonic saline. The degree of recirculation is calculated from the difference in conductivity between arterial and venous sensors.

Potassium dilution – Recirculation is determined by the dilution of potassium in blood drawn from the arterial line following an injection of normal saline [7].

Urea-based methods — Urea-based methods do not require additional equipment. However, since blood samples need to be sent out for measurement of urea, there is a delay in obtaining a result. Urea-based methods include the two-needle stopped or slow stop-flow technique and the three-needle urea-based techniques. As noted above, if a urea-based method is used, the two-needle slow or stop-blood flow technique is preferred.

Recirculation that is >10 percent by a urea-based method should prompt further evaluation (ie, fistulography). (See "Clinical monitoring and surveillance of the mature hemodialysis arteriovenous fistula", section on 'Indications for angiography referral' and "Clinical monitoring and surveillance of hemodialysis arteriovenous grafts to prevent thrombosis", section on 'Indications for referral'.)

The two-needle stopped or slow stop-flow technique and the three-needle urea-based techniques are discussed below.

Two-needle stopped or slow stop-flow technique – In the two-needle stopped blood flow technique, the blood urea nitrogen (BUN) is measured in blood obtained from the arterial needle after blood flow has been stopped. In the two-needle slow blood flow technique, the systemic BUN is measured in blood obtained from the arterial needle after blood flow has been reduced to 50 mL/min. Both techniques allow accurate determination of the BUN concentration in blood entering the access. The low blood flow technique is preferred because of greater ease of performance [8].

The standard protocol for performing the low blood flow technique is as follows [9]:

Turn off ultrafiltration approximately 30 minutes after the initiation of hemodialysis.

Obtain arterial and venous line samples.

Reduce access blood flow to 50 mL/min.

Obtain the systemic blood sample from the arterial blood line after sufficient time has passed to clear 150 percent of the volume between the arterial needle and the sampling point, but no later than 30 seconds after the reduction of access flow to 50 mL/min.

Three-needle urea-based technique – The three-needle urea-based approach used to be the common method for measuring recirculation. We agree with the 2006 KDOQI guidelines that the three-needle urea-based approach not be used to measure recirculation [5]. This method involved obtaining simultaneous measurement of BUN from the peripheral blood, predialyzer arterial line, and postdialyzer venous circuit.

The three-needle method overestimates recirculation. This is because the BUN obtained from a peripheral vein in the contralateral (ie, nonaccess) arm is often higher than the BUN in the blood entering the access, even in the absence of recirculation. BUN is higher in blood obtained from the nonaccess arm because of the following [9]:

Arteriovenous disequilibrium (also called cardiopulmonary recirculation)

Venovenous disequilibrium

Arteriovenous disequilibrium occurs when dialyzed blood (thus with a low urea concentration) returns to the central veins and dilutes the blood returning from the systemic circulation, which has a high urea concentration. The net effect is that the urea concentration in central venous blood and, therefore, in blood leaving the left heart and entering the hemodialysis access, is lower than the urea concentration in peripheral venous blood.

Venovenous disequilibrium results from decreased perfusion of the contralateral arm (and other tissue beds) during dialysis [9]. As a result, urea removal in that limb is diminished in comparison to well-perfused compartments. Thus, the urea concentration in the veins of the contralateral arm is higher than in central venous blood or blood entering the fistula. This difference increases with time [10].

In addition to inaccuracies in the measurement of BUN, this method requires that peripheral blood be drawn from a separate needle stick.

CATHETER RECIRCULATION — When hemodialysis catheters are unable to achieve adequate blood flow (>300 mL/min), a common temporary strategy to increase flow is to reverse the line position (in which blood is withdrawn from the venous port and returned via the arterial port). Although studies have suggested that this maneuver increases arteriovenous fistula recirculation (5 to approximately 15 percent or even higher) [11-15], the improved blood flow attained with line reversal may improve the overall clearance in dysfunctional catheters. This was evaluated in one study of 14 patients with dysfunctional catheters [11]. Although line reversal markedly increased access recirculation (0 to 25 percent), the enhanced blood flow was associated with a significant increase in the mean urea clearance (128 mL/min at a flow of 200 mL/min to 157 mL/min at maximal blood flow). Thus, overall clearance was increased.

Current guidelines suggest, however, that poorly functioning catheters should undergo prompt evaluation and proper treatment to ensure adequate blood flow. (See "Malfunction of chronic hemodialysis catheters".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Dialysis".)

SUMMARY AND RECOMMENDATIONS

Definition – Hemodialysis access recirculation is an important cause of inadequate dialysis delivery to individual patients. Recirculation occurs when dialyzed blood returning through the venous needle re-enters the extracorporeal circuit through the arterial needle, rather than returning to the systemic circulation. This reduces solute concentration gradients across the dialysis membrane and reduces the efficiency of dialysis. (See 'Introduction' above and 'Definition and mechanism' above.)

Causes – Causes of recirculation include venous stenosis and arterial stenosis, both of which lead to low access blood flow. (See 'Causes' above.)

When to measure recirculation – The major indication to measure recirculation in patients with either a fistula or graft is that the delivered Kt/V is below target despite an adequate hemodialysis prescription. Finding significant recirculation may lead to the identification and correction of stenosis.

Monitoring recirculation may also be used as a surveillance method of screening for fistula stenosis among patients who have no evidence of inadequate delivered Kt/V. However, other methods are generally preferred since recirculation is a late marker for stenosis. Recirculation should not be used to screen for stenosis in grafts. (See 'Indications for measuring recirculation' above.)

Methods of measuring recirculation – Methods of measuring recirculation include non-urea-based indicator dilutional methods and urea-based methods. The preferred methods are non-urea-based dilutional methods. (See 'Methods of measuring recirculation' above.)

Non-urea-based methods – Common non-urea-based methods include ultrasound velocity dilution, thermal dilution, optical dilution, conductivity dilution, and potassium dilution. A recirculation value above 5 to 10 percent detected by a non-urea-based method should prompt fistulography. Some clinicians use a 5 percent threshold whereas others use a 10 percent threshold. (See 'Non-urea-based indicator dilutional methods' above.)

Urea-based methods – If a urea-based method is used, the two-needle stopped- or slowed-flow recirculation approach should be used rather than the more traditional three-needle approach. This is consistent with the 2006 Kidney Disease Outcomes Quality Initiative (KDOQI) recommendations. Recirculation that is >10 percent by a urea-based method should prompt fistulography. (See 'Urea-based methods' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Michael Berkoben, MD, who contributed to earlier versions of this topic review.

  1. Dinwiddie LC, Ball L, Brouwer D, et al. What nephrologists need to know about vascular access cannulation. Semin Dial 2013; 26:315.
  2. Basile C, Ruggieri G, Vernaglione L, et al. A comparison of methods for the measurement of hemodialysis access recirculation. J Nephrol 2003; 16:908.
  3. Coyne DW, Delmez J, Spence G, Windus DW. Impaired delivery of hemodialysis prescriptions: an analysis of causes and an approach to evaluation. J Am Soc Nephrol 1997; 8:1315.
  4. Schneditz D, Ribitsch W, Keane DF. Intradialytic techniques for automatic and everyday access monitoring. Semin Dial 2023.
  5. Hemodialysis Adequacy 2006 Work Group. Clinical practice guidelines for hemodialysis adequacy, update 2006. Am J Kidney Dis 2006; 48 Suppl 1:S2.
  6. Bodington R, Greenley S, Bhandari S. Getting the basics right: the monitoring of arteriovenous fistulae, a review of the evidence. Curr Opin Nephrol Hypertens 2020; 29:564.
  7. Brancaccio D, Tessitore N, Carpani P, et al. Potassium-based dilutional method to measure hemodialysis access recirculation. Int J Artif Organs 2001; 24:606.
  8. Sherman RA, Matera JJ, Novik L, Cody RP. Recirculation reassessed: the impact of blood flow rate and the low-flow method reevaluated. Am J Kidney Dis 1994; 23:846.
  9. Sherman RA. The measurement of dialysis access recirculation. Am J Kidney Dis 1993; 22:616.
  10. Depner TA, Rizwan S, Cheer AY, et al. High venous urea concentrations in the opposite arm. A consequence of hemodialysis-induced compartment disequilibrium. ASAIO Trans 1991; 37:M141.
  11. Carson RC, Kiaii M, MacRae JM. Urea clearance in dysfunctional catheters is improved by reversing the line position despite increased access recirculation. Am J Kidney Dis 2005; 45:883.
  12. Atherikul K, Schwab SJ, Conlon PJ. Adequacy of haemodialysis with cuffed central-vein catheters. Nephrol Dial Transplant 1998; 13:745.
  13. Depner TA, Krivitski NM, MacGibbon D. Hemodialysis access recirculation measured by ultrasound dilution. ASAIO J 1995; 41:M749.
  14. Senécal L, Saint-Sauveur E, Leblanc M. Blood flow and recirculation rates in tunneled hemodialysis catheters. ASAIO J 2004; 50:94.
  15. Pannu N, Jhangri GS, Tonelli M. Optimizing dialysis delivery in tunneled dialysis catheters. ASAIO J 2006; 52:157.
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