Continuous wave Doppler methods to dialysis access monitoring.

Dialysis access failure is the major cause of morbidity among patients undergoing hemodialysis. Reduced blood flow reveals access malfunction. This work discusses two methods based on directional continuous wave Doppler system to evaluate the access blood flow. By changing the dialysis blood pump flow rate, the variable flow Doppler method measures the access blood flow. Software was developed to make feasible its application during clinical routine. A second method proposes the spectral broadening index (SBI) to characterize the access performance. Preliminary results show that a SBI above 1.9 denotes poor blood flow (less than 600ml/min. Sensibility=80%. Specificity=83%). According to the National Kidney Foundation, patients whose access flow is inferior to 600 ml/min should be referred for fistulogram. The second method is easier to be applied in dialysis sessions.