Effective Ionic Dialysance/Blood Flow Rate Ratio: An Indicator of Access Recirculation in Arteriovenous Fistulae

Intradialytic techniques for automatic and everyday access monitoring

Vascular access dysfunction is associated with reduced delivery of dialysis, unplanned admissions, patient symptoms, and loss of access, making assessment of vascular access a fundamental part of routine care in dialysis. Clinical trials to predict the risk of access thrombosis based on accepted reference methods of access performance have been disappointing. Reference methods are time-consuming, affect the delivery of dialysis, and therefore cannot repeatedly be used with every dialysis session. There is now a new focus on data continuously and regularly collected with every dialysis treatment, directly or indirectly associated with access function, and without interrupting or affecting the delivered dose of dialysis. This narrative review will focus on techniques that can be used continuously or intermittently during dialysis, taking advantage of methods integrated into the dialysis machine and which do not affect the delivery of dialysis. Examples include extracorporeal blood flow, dynamic line pressures, effective clearance, dose of delivered dialysis, and recirculation which are all routinely measured on most modern dialysis machines. Integrated information collected throughout every dialysis session and analyzed by expert systems and machine learning has the potential to improve the identification of accesses at risk of thrombosis.

Evaluation of partial pressure CO2 change in the dialyzer blood inlet during hemodialysis as a measure of vascular access recirculation

INTRODUCTION

Vascular access recirculation during hemodialysis is associated with reduced effectiveness and worse survival outcomes. To evaluate recirculation, an increase in pCO2 in the blood of the arterial line during hemodialysis (threshold of 4.5 mmHg) was proposed. The blood returning from the dialyzer in the venous line has significantly higher pCO2 , so in the presence of recirculation, pCO2 in the arterial blood line may increase (ΔpCO2 ) during hemodialysis sessions. The aim of our study was to evaluate ΔpCO2 as a diagnostic tool for vascular access recirculation in chronic hemodialysis patients.

METHODS

We evaluated vascular access recirculation with ΔpCO2 and compared it with the results of a urea recirculation test, which is the gold standard. ΔpCO2 was obtained from the difference in pCO2 in the arterial line at baseline (pCO2 T1) and after 5 min of hemodialysis (pCO2 T2). ∆pCO2  = pCO2 T2-pCO2 T1.

FINDINGS

In 70 hemodialysis patients (mean age: 70.52 ± 13.97 years; hemodialysis vintage of 41.36 ± 34.54, KT/V 1.4 ± 0.3), ∆pCO2 was 4 ± 4 mmHg, and urea recirculation was 7% ± 9%. Vascular access recirculation was identified using both methods in 17 of 70 patients, who showed a ∆pCO2 of 10 ± 5 mmHg and urea recirculation of 20% ± 9%; time in months of hemodialysis was the only difference between vascular access recirculation and non-vascular access recirculation patients (22 ± 19 vs. 46 ± 36, p: 0.05). In the non-vascular access recirculation group, the average ΔpCO2 was 1.9 ± 2 (p: 0.001), and the urea recirculation % was 2.8 ± 3 (p: 0.001). The ΔpCO2 correlated with the urea recirculation % (R: 0.728; p < 0.001).

DISCUSSION

ΔpCO2 in the arterial blood line during hemodialysis is an effective and reliable diagnostic tool for identifying recirculation of the vascular access but not its magnitude. The ΔpCO2 test application is simple and economical and does not require special equipment.

Comparison of urea recirculation and thermodilution for monitoring of vascular access in patients undergoing hemodialysis

Introduction

It is important to monitor vascular access in patients with stage 5 chronic kidney disease receiving hemodialysis. Access recirculation can help to detect a need for intervention.

Objectives:

To compare urea recirculation with recirculation by thermodilution using blood temperature monitoring to predict a need for intervention of vascular access over a 6-month period.

Methods:

We analyzed urea recirculation and blood temperature monitoring simultaneously in 61 patients undergoing hemodialysis. During the 6-month follow-up, we recorded all cases of angioplasty or surgery (thrombectomy or reanastomosis). In line with previous studies, we considered a value to be positive when urea recirculation was >10% and blood temperature monitoring >15%. Receiver operating characteristic curves were constructed.

Results:

Mean urea recirculation was 9.5% ± 6.6% and mean blood temperature monitoring 12.9% ± 4.3% (p = 0.001). Urea recirculation >10% had a sensitivity of 80% and specificity of 78%. Blood temperature monitoring >15% had a sensitivity of 33% and specificity of 85%. During follow-up, 25% of patients developed need for intervention of vascular access. We found an association between vascular access dysfunction and urea recirculation. The Kaplan–Meier analysis confirmed an association between urea recirculation and risk of vascular access dysfunction (log rank = 17.2; p = 0.001). We were unable to confirm this association with blood temperature monitoring (log rank = 0.879; p = 0.656).

Conclusion:

Urea recirculation is better predictor of vascular access dysfunction than thermodilution.

Integrating Real Time Data to Improve Outcomes in Acute Kidney Injury

Critically ill patients with acute kidney injury requiring renal replacement therapy have a poor prognosis. Despite well-known factors, which contribute to outcomes, including dose delivery, patients frequently miss the target dose and volume removal. One major barrier to effective care of these patients is the traditional dissociation of dialysis device data from other clinical information systems, notably the electronic health record (EHR). This lack of integration and the resulting manual documentation leads to errors and biases in documentation and missed opportunities to intervene in a timely fashion. This review summarizes the technological advancements facilitating direct connection of dialysis devices to EHRs. This connection facilitates automated data capture of many variables - including delivered dose, ultrafiltration rate and pressure measurements - which in turn can be leveraged for data mining, quality improvement and real-time targeted therapy adjustments. These interventions hold the promise to significantly improve outcomes for this patient population.

Observational study of surveillance based on the combination of online dialysance and thermodilution methods in hemodialysis patients with arteriovenous fistulas

BACKGROUND/AIMS

Online dialysance (Kt) and thermodilution (BTM-Qa) methods could be important components in vascular access monitoring programs. This study evaluated the efficiency of these two methods in reducing the thrombosis rate and access-related costs compared with a historic control group.

METHODS

We studied 148 hemodialysis patients with arteriovenous fistulas (control group, n = 74) for 2 years. During the study period, the indications for vascular treatments were the Kt reduction ≥20% with respect to baseline values or Qa <500 ml/min (or a decrease in flow >20%).

RESULTS

During the study period, we detected 16 cases of vascular dysfunction. The Kt value after vascular treatment was 71.1 liters (59 liters; p = 0.001) and BTM-Qa was 1,218.6 ml/min (519.7 ml/min; p = 0.001). Compared with the control group, the thrombosis rate was 0.027 versus 0.148 episodes/patient-year (p = 0.009) and the total access-related cost was EUR 22,293 versus 47,467 (p = 0.033).

CONCLUSIONS

This study suggests that a combined monitoring program based on Kt and BTM-Qa represents an effective screening method that significantly reduces the thrombosis rate and economic costs of vascular treatments.

Study of discrepancies between recorded and actual blood flow in hemodialysis patients

Adequate blood flow (Qb) is necessary for effective hemodialysis (HD). Aim of the study was to examine relationship between the actually delivered Qb (dQb) and reported Qb (rQb) with dialysis machine. One hundred HD patients with arteriovenous fistula were enrolled. Delivered Qb was measured at the beginning and end of each HD session. dQb/rQb < 1 indicated a discrepancy between actual dQb and rQb reported using a dialysis machine. In addition, dQb/rQb was examined in HD patients using needles of different gauges during treatment. The average levels of dQb/rQb at start and end of HD session were 1.01 ± 0.04 and 0.98 ± 0.05, respectively. In the 16 gauge and 17 gauge needle groups, the percentage of patients with dQb/rQb < 1 increased in accordance with the increase in rQb or as the HD session progressed. In the 15 gauge needle group, the percentage of patients with dQb/rQb < 1 was <50% at any level of rQb. Selection of needle gauge is important factors for determining actual dQb in HD patients.

Evaluation of Alternatives for Dysfunctional Double Lumen Central Venous Catheters Using a Two-Compartmental Mathematical Model for Different Solutes

Double lumen (DL) central venous catheters (CVC) often suffer from thrombosis, fibrin sheet formation, and/or suction towards the vessel wall, resulting in insufficient blood flow during hemodialysis. Reversing the catheter connection often restores blood flows, but will lead to higher recirculation. Single lumen (SL) CVCs have often fewer flow problems, but they inherently have some degree of recirculation. To assist bedside clinical decision making on optimal catheter application, we investigated mathematically the differences in dialysis adequacy using different modes of access with CVCs.

A mathematical model was developed to calculate reduction ratio (RR) and total solute removal (TSR) of urea, methylguanidine (MG), beta-2-microglobulin (β2M), and phosphate (P) during different dialysis scenarios: 4-h dialysis with a well-functioning DL CVC (DL-normal, blood flow QB 350 ml/min), dysfunctional DL CVC (DL-low flow, QB 250), reversed DL CVC (DL-reversed, QB 350, recirculation R = 10%) and 12 Fr SL CVC (effective QB273).

With DL-normal as reference, urea RR was decreased by 3.5% (DL-reversed), 13.0% (SL), and 15.6% (DL-low flow), while urea TSR was decreased by 3.3% (DL-reversed), 13.2% (SL), and 13.5% (DL-low flow). The same trend was found for MG and P. However, β2M RR decreased only 1.5% with SL CVC although TSR decrease was 17.2%, while RR decreased 21.1% with DL-low flow although TSR decrease was only 4.9%.

In the case of dysfunctional DL CVCs, reversing the catheter connection and restoring the blood flow did not impair TSR, with 10% recirculation. The SL CVC showed suboptimal TSR results that were similar to those of the dysfunctional DL CVC.

More may be less: increasing extracorporeal blood flow in an axillary arterio-arterial access decreases effective clearance

Axillary arterio-arterial graft interposition has been described as a reasonable haemodialysis access in selected patients. In a patient with this unusual access, we measured and calculated effective clearance at different extracorporeal blood flows (Q(b)). Effective clearance increased with increasing blood flow and reached a maximum at a Q(b) of ~200 mL/min but then decreased when Q(b) was increased further. As this type of access typically provides low access flow, one has to be aware that local recirculation will easily occur. Therefore, a Q(b) above access flow has to be avoided since any increase beyond that threshold reduces effective clearance.