Comparison of hemodialysis blood access flow rates using online measurement of conductivity dialysance and ultrasound dilution

Routine online assessment of dialysis dose: Ionic dialysance or UV-absorbance monitoring?

For three-weekly hemodialysis, a single-pool Kt/V target of at least 1.4 together with a minimal dialysis dose Kt at 45 L for men and 40 L for women per each session is currently recommended. Fully automatic online calculation of Kt and Kt/V from conductivity or UV-absorbance measurements in the dialysate is standardly implemented on some hemodialysis monitors and makes it possible to estimate the dialysis dose without the need for blood or dialysate samples. Monitoring the UV-absorbance of the spent dialysate is the most direct method for estimating Kt/V as it does not require an estimate of V. Calculation of ionic dialysance from conductivity measurements is the most direct method for estimating Kt and BSA-scaled dialysis dose. Both ionic dialysance monitoring and UV-absorbance monitoring may help detect a change in urea clearance occurring during the session, but this change must be interpreted differently depending on the monitoring being considered. An abrupt decrease in urea clearance results in a decrease in ionic dialysance but, paradoxically, a sudden increase in estimated urea clearance provided by dialysate UV-absorbance monitoring. Healthcare teams who monitor both ionic dialysance and UV-absorbance in their hemodialysis units must be clearly informed of this difficulty.

Online measurement of hemodialysis adequacy using effective ionic dialysance of sodium-a review of its principles, applications, benefits, and risks

Dialysis dose is an important determinant of clinical outcomes in patients with end stage renal disease on maintenance dialysis. In clinical practice dialysis dose is monitored at least monthly by urea clearance based on Urea Kinetic Modeling. Online clearance monitoring using effective ionic dialysance (EID) of sodium (Na⁺ ) is available on some hemodialysis machines. This paper reviews the background, methodology, additional applications, and potential risks associated with EID. Effective ionic dialysance provides a reliable, real-time, noninvasive, and inexpensive measurement of dialysis dose during an ongoing hemodialysis (HD) session to allow interventions and assess the impact of these changes on clearance. Surveillance of vascular access flow rates can be used to screen for access dysfunction and refer for interventions. There is a concern that EID measurements may cause Na⁺ loading because of high dialysate Na⁺ used during these measurements, however, mathematical models, in vitro experiments, and clinical studies in patients on maintenance HD do not show any evidence of Na⁺ loading during EID measurements. We cannot rule out the possibility of nonosmotic Na⁺ accumulation in the skin because no published literature exists on this topic as it pertains to clearance measurements based on EID of Na⁺ .

Vascular Access Monitoring and Surveillance: An Update

Vascular access in dialysis patients remains both a critical link to survival and a significant source of morbidity. Currently, the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF-KDOQI) vascular access guidelines recommend routine vascular access monitoring and encourage dedicated surveillance techniques to be used for early detection of access stenosis and prevention of thrombosis. There is a paucity of clear evidence supporting 1 surveillance technique over another. The purpose of this review is to describe the benefits and limitations of various surveillance techniques commonly used in the care of dialysis patients. Further studies in this area will be useful to determine the most appropriate combination of aggressive clinical monitoring and additional surveillance data to strike a balance between graft thrombosis and unnecessary vascular interventions.

Surveillance of hemodialysis vascular access

A mature, functional arteriovenous (AV) access is the lifeline for a hemodialysis (HD) patient as it provides sufficient enough blood flow for adequate dialysis. As the chronic kidney disease (CKD) and end-stage renal disease (ESRD) population is expanding, and because of the well-recognized hazardous complications of dialysis catheters, the projected placement and use of AV accesses for HD is on the rise. Although a superior access than catheters, AV accesses are not without complications. The primary complication that causes AV accesses to fail is stenosis with subsequent thrombosis. Surveying for stenosis can be performed in a variety of ways. Clinical monitoring, measuring flow, determining pressure, and measuring recirculation are all methods that show promise. In addition, stenosis can be directly visualized, through noninvasive techniques such as color duplex imaging, or through minimally invasive venography. Each method of screening has its advantages and disadvantages, and several studies exist which attempt to answer the question of which test is the most useful. Ultimately, to maintain the functionality of the access for the HD patient, a team approach becomes imperative. The collaboration and cooperation of the patient, nephrologist, dialysis nurse and technician, vascular access coordinator, interventionalist, and vascular surgeon is necessary to preserve this lifeline.

The measurement of hemodialysis access blood flow by a conductivity step method

BACKGROUND AND OBJECTIVES

Measurement of blood flow rate (Qa) is used to monitor dialysis access, AV fistulas, and grafts. Indicator dilution measurements of the recirculation (R) induced by reversal of hemodialysis blood lines are commonly used. This plus the dialysis circuit flow (Qb) allows calculation of Qa. R also changes the conductivity, which can be measured by a conductivity cell in the spent dialysate. The change in conductivity caused by line reversal should vary with Qa. A methodology for Qa measurement utilizing this conductivity step is proposed. This study compares conductivity step methodology against the reference method of ultrasound dilution (Qa-Trans).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was an open diagnostic test study in a single academic hospital setting involving 15 hemodialysis-dependent patients. Each was studied over four hemodialysis treatments. During each treatment, two pairs of Qa measurements (conductivity step and Trans) were made. Pre- and postdialysis sodium levels were also measured.

RESULTS

Average Qa-conductivity step was 1040 ml/min. Average Qa-Trans was 1030 ml/min. The difference was NS. The data pairs showed mean difference of 1.3 +/- 17% (SD). The SD indicates a relatively large variation between data pairs. There was significant linear correlation between the Qa-conductivity step and Qa-Trans results (r = 0.91, P < 0.001). Serum sodium rose slightly but significantly over dialysis (P < 0.001).

CONCLUSIONS

Qa measurement by conductivity step may be an acceptable alternative to ultrasound dilution methodology. Care must be taken to prevent salt loading when the conductivity step is used.

Comparison of hemodialysis access flow measurements using flow dilution and in-line dialysance

Measurement of hemodialysis (HD) access flow (QA) is a noninvasive approach for arteriovenous graft or fistula surveillance. Flow dilution (FD) and in-line dialysance (DD) are two common methods for measuring QA. In a randomized fashion, we prospectively evaluated QA using FD and DD in 48 HD patients during three separate HD sessions over a span of 3 months. The measurement of QA was similar (1,016 +/- 412 ml/min for FD and 1,009 +/- 425 ml/min for DD, p = 0.44 and 0.79 for the mean and standard deviation, respectively). While FD successfully measured QA >or=2,000 ml/min, DD "saturated" (indicating a QA >or=2,000 ml/min without providing a numerical QA value) (n = 17). The correlation coefficient for QA <or=2,000 ml/min between DD and FD measurements from the same dialysis sessions was high (r = 0.9, p < 0.001) with a straight line slope of 0.997. Access flow values for FD and DD methods were comparable at QA <or=2,000 ml/min and no single method tended to over- or underestimate QA compared with the other. For QA >2,000 ml/min, FD provided a quantitative QA measure, and is therefore a potentially useful tool for QA above this threshold, while DD is not.