New EID/Qb technique offers real-time monitoring of AVF function during dialysis

Sep 24 2010

A simple equation provides real-time feedback to detect access recirculation in arteriovenous fistulas (AVFs) during hemodialysis, reports a study in the September/October issue of ASAIO Journal, Official Journal of the American Society of Artificial Internal Organs. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health, a leading provider of information and business intelligence for students, professionals, and institutions in medicine, nursing, allied health, pharmacy and the pharmaceutical industry.

Arteriovenous fistulas have become the preferred form of vascular access in chronic hemodialysis patients, as they make dialysis safer and easier for patients. However, problems related to fistula stenoses (narrowing) can develop over time. Early detection and correction of stenoses can help to prevent inadequate dialysis and other complications.

Dividing the effective ionic dialysance (EID) by the blood flow rate (Qb) to calculate the "EID/Qb ratio" provides an accurate tool to screen for the problem of recirculation in AVFs used for dialysis access, according to the new study. Other techniques proposed to detect access recirculation as an indicator of AVF function have been impractical for routine use. "Obtaining this ratio is potentially simple, noninvasive, and uses widely available standard equipment with no additional cost," write Dr. Sumit Mohan and colleagues of Columbia University College of Physicians and Surgeons, New York.

Automatically Calculated Ratio Detects Problems with AVF Function
Access recirculation occurring in the AVF is a sign of fistula stenosis or other causes of inadequate flow rates. Particularly at the high flow rates used in modern high-efficiency hemodialysis systems, some convenient and accessible means of detecting access recirculation is needed.

Dr. Mohan and colleagues designed a study to evaluate the use of the EID/Qb ratio, automatically calculated by the dialysis system during treatment, as an indicator of access recirculation problems. The study included 47 dialysis patients with AVFs. In a total of 323 hemodialysis sessions, the standard saline dilution technique detected access recirculation in 17 cases—a rate of 5.3 percent.

The EID/Qb ratio performed well in detecting access recirculation. At a value of 50 percent or less, the EID/Qb ratio correctly identified 76.5 percent of patients with access recirculation (sensitivity), while ruling out access recirculation in 96.4 percent of patients who did not have it (specificity).

In two cases, access recirculation was caused by inadvertent reversal of the hemodialysis blood lines—these were also detected by the EID/Qb ratio. The ratio performed similarly well when dialysis was performed using a high-efficiency dialysis machine and on a slower flow-rate machine.

The EID is a relatively new measure of dialysis dose, depending partly on the blood flow rate. The EID/Qb ratio can be easily and continuously calculated by the dialysis equipment, providing real-time feedback on AVF function.

The new study suggests that the EID/Qb ratio is a useful technique for routine monitoring of AVF function during dialysis sessions. It offers good accuracy in identifying patients with possible AVF problems in need of further evaluation. It also appears useful in monitoring for technical problems such as line reversal or needle malposition. "The EID/Qb ratio is an excellent online chairside test for identifying access recirculation during hemodialysis in patients with AVF," Dr. Mohan and colleagues conclude.