Flow measurements in dialysis shunts: lack of agreement between conventional Doppler, CVI-Q, and ultrasound dilution

Background. Measuring flow in dialysis shunts is recommended to predict imm inent thrombosis. Multiple use. Numerous ultrasound protocols exist which d eter-mine volume flow using a conventional Doppler (CD) frequency shift ana lysis technique. All of these are subject to potentially large errors. Quan titative colour velocity index (CVI-Q) does not make use of the Doppler equ ation and is more precise in vitro Ultrasound dilution (UD) measures access flow during dialysis in a non-operator-dependent way. The aim of the prese nt study was to compare these three methods of measuring access flow in viv o for agreement with each other. Methods. In 38 accesses flow was measured by CD, CVI-Q, and UD. All measure ments were done during dialysis. Agreement was determined by intraclass cor relation coefficient (ICC = R-i) and Bland-Altman analysis. Results. ICC between UD and CVI-Q was R-i = 0.56. ICC between UD and CD was R-i = 0.10, and ICC between CD and CVI-Q was R-i = 0.16. Bland-Altman anal ysis revealed a bias (mean difference)of -38 ml/min between UD and CVI-Q, a bias of 1129 ml/min between UD and CD, and a bias of 1167 ml/min between C VI-Q and CD. Conclusions. CD measurements did not agree with UD or CVI-Q: much higher va lues were recorded with the former than with the latter two techniques. The agreement between UD and CVI-Q measurements is low but reasonable. Caution must be applied in comparing and interpreting values of access flow measur ed by different techniques.