Variable Pump Flow–Based Doppler Ultrasound Method: A Novel Approach to the Measurement of Access Flow in Hemodialysis Patients Chih-Ching Lin,* ¶ Chao-Fu Chang,* ¶ Hong-Jen Chiou, §¶ Ying-Chou Sun, ‡ Shou-Shan Chiang, # Ming-Wei Lin, ‡¶ Pui-Ching Lee, † and Wu-Chang Yang* ¶ *Division of Nephrology, † Department of Medicine, ‡ Department of Medical Research, and § Division of Ultrasound, Department of Radiology, Taipei Veterans General Hospital, Taipei, Taiwan;  Institute of Clinical Medicine, ¶ Faculty of Medicine, National Yang-Ming University, Taipei, Taiwan; and # Division of Nephrology, Department of Medicine, Shin Kong Wu Ho-Su Memorial Hospital Decreasing vascular access flow (Qa) is an important predictor of future access thrombosis and malfunction for hemodialysis (HD) patients. Among all of the methods for determining Qa, the variable pump flow (VPF) Doppler method measures Qa according to the change in Doppler signal between the arterial and the venous needles under different pump flow. After this technique was combined with spectral analysis of Duplex Doppler imaging, the variable pump flow– based Doppler ultrasound method (VPFDUM) for Qa measurement was developed. This study compared the reproducibility and correlation of Qa measurements for three different methods—VPFDUM, ultrasound dilution method (UDM), and conventional Doppler ultrasound method (CDUM)—in 55 HD patients. The mean value of Qa by VPFDUM (870.8  412.0 ml/min) was close to that by UDM (868.6  417.9 ml/min) but higher than that by CDUM (either of the above values versus 685.1  303.6 ml/min; P < 0.005). The mean values of coefficient of variation were similar by VPFDUM (1.6%) and UDM (1.4%) but lower than that by CDUM (either of the above values versus 6.8%; P < 0.01). The correlation coefficient and intraclass correlation coefficient of the repeated Qa measurements by VPFDUM (0.985 and 0.993; P < 0.001) were also similar to those by UDM (0.992 and 0.995; P < 0.001) but slightly higher than those by CDUM (0.917 and 0.948; P < 0.005). Either the reproducibility of VPFDUM (r  0.98, P < 0.0001) or the correlation between VPFDUM and UDM (r  0.99, P < 0.0001) in Qa measurements is good. The unassisted patency of vascular access at 6 mo was significantly poorer in patients with Qa <500 ml/min than those with Qa >500 ml/min (13.6% versus 92.2%; P < 0.0001). In conclusion, VPFDUM is a noninvasive, accurate, and reliable procedure for Qa measurement and prediction of the prognosis of vascular access in HD patients. J Am Soc Nephrol 16: 229 –236, 2005. doi: 10.1681/ASN.2004040266 T he malfunction of vascular access accounts for consid- erable morbidity and mortality in hemodialysis (HD) patients. It is responsible for 17 to 25% of all hospital- izations among dialysis patients in the United States (1,2). Treatment of these problems requires invasive, expensive, and time-consuming procedures, which are associated with poten- tial risk of complication. Failure of dialysis access can result from either inadequate blood flow on account of stenosis of the venous outflow tract or complete occlusion as a result of throm- bosis (3). Decreased access flow is associated with an increased risk for access thrombosis. Access flow (Qa) 400 ml/min in native arteriovenous fistulas (AVF) and 800 ml/min in poly- tetrafluoroethylene (PTFE) grafts was demonstrated to be pre- dictive of access failure in one ultrasonographic study of 477 AVF and 831 PTFE grafts (4). The methods of measuring Qa include dye dilution (5), constant infusion of technetium-99m (6), Doppler ultrasonography (7), electromagnetic flow meters (8), and magnetic resonance angiography (9). However, some of the above methods are invasive or highly technique depen- dent, and some require additional laboratory tests. Some of them are impractical and costly or cannot be performed during HD. In the past few years, several noninvasive techniques have been developed for calculating Qa, including ultrasound dilu- tion (10), photo-optical sensor (11), conductivity dialysance (12), thermodilution (13), and ultrafiltration method (14). Among these methods, the ultrasound dilution method (UDM), developed by Krivitski (10), has been widely accepted as a practical, reliable, and noninvasive method for Qa mea- surement. Besides, color Doppler ultrasound method addition- ally provides an anatomic picture of a dialysis access and its venous runoff. It not only is noninvasive but also can be per- formed serially. However, both of these methods have short- comings that limit their application in access surveillance. UDM is time-consuming and requires dialysis blood line rever- sal. Duplex imaging is subject to operator-dependent error and Received April 3, 2004. Accepted September 26, 2004. Published online ahead of print. Publication date available at www.jasn.org. Address correspondence to: Dr. Wu-Chang Yang, Division of Nephrology, De- partment of Medicine, Veterans General Hospital-Taipei, No. 201, Sec. 2, Shih-Pai Road, Taipei, Taiwan 112, Republic of China; Phone: 886-2-2875-7517; Fax: 886- 2-2873-1582; E-mail: wcyang@vghtpe.gov.tw Copyright © 2005 by the American Society of Nephrology ISSN: 1046-6673/1601-0229