The use of a Diasonics DRF400 duplex ultrasound scanner to measure volume flow in arterio-venous fistulae in patients undergoing haemodialysis: an analysis of measurement uncertainties.

A pilot study to measure volume flow in arterio-venous fistulae in patients undergoing haemodialysis was undertaken to determine the accuracy and precision of values obtained using a modern duplex ultrasound scanner. A Diasonics DRF400 duplex ultrasound scanner was used with a small parts 10 MHz mechanical sector probe incorporating a 4.5 MHz Doppler transducer. Volume flow was measured in the brachial artery of 13 patients with surgically created arterio-venous fistulae in the distal circulation. Volume flow was also measured using a flow phantom in which the true volume flow was known. An analysis of the measurements made by the duplex scanner was performed to determine the sources of random and systematic uncertainty. Repeatability was improved with the probe clamped in position over the brachial artery giving a coefficient of variation in repeated measurements of volume flow in a patient of +/- 12%. Measured flows ranged from 884-3088 mL min-1. Comparison with measurements on the flow phantom showed these values from patients to be overestimated by 200-600 mL min-1. The values from the phantom should therefore be used to calibrate patient measurements. Analysis of uncertainties showed that precision was limited by random uncertainties in the measurement of vessel diameter and Doppler angle.