Hemodialysis Access by Sherene Shalhub Anahita Dua & Susanna Shin

Author:Sherene Shalhub, Anahita Dua & Susanna Shin
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Direct Methods to Measure Access Flow

(a)Dilution Methods: These methods are based on Fick’s principle. During dialysis, saline is injected in the dialysis tubing, and either an ultrasound (US) or heat or light sensor is employed to measure the dilution of blood through the dialysis lines, and the data are used to calculate access flow rates. The exact method involves switching of arterial and venous segments of lines so that the arterial line is downstream from the venous return line (Fig. 20.6), and, therefore, the dialyzed blood being returned into the access is picked up (recirculated) by the arterial line feeding the blood into the dialyzer. Flow dilution sensors are clamped on the arterial and venous segments, a saline bolus is injected into the venous line, and dilution sensor measures the amount of dilution. This diluted blood goes through the access, and a part of this diluted blood gets aspirated into the arterial segment by the blood pump. The volume of dialyzed blood being returned to the dialysis system represents recirculation (R), and is caused by reversal of the lines. The dilution sensor in the arterial line measures the extent of dilution (R). Comparison of the two values (dilution in venous and arterial segments) gives the access flow rates by the following relationship:

Fig. 20.6Showing saline dilution method to measure recirculation and access flow. Note lines are switched, access flow is from left to right, venous needle is upstream and arterial needle downstream. Venous & arterial dilution sensors are clamped on the arterial & venous lines and connected to US

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