Input impedance of radiocephalic arteriovenous fistulae for haemodialysis access: its value in predicting early failure

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Abstract
This study is concerned with an assessment of the quality of the blood vessels used in the construction of radiocephalic arteriovenous fistulae for haemodialysis vascular access in 20 patients. Following non-invasive preoperative assessment of the cephalic vein by means of a colour Doppler scanner, input impedance was determined intraoperatively from blood flow and blood pressure measured about 2 cm downstream of the anastomosis. The patients were re-assessed 1 day and 2, 4, 6 and 12 weeks after surgery, and the diameter and the flow through the fistulae, the location of major branches, and the presence and severity of stenoses in the cephalic veins were determined non-invasively. Five fistulae failed within the 12 weeks period following surgery, mainly due to thrombosis. In a further 3 patients, the fistulae were patent but did not achieve an adequately high blood flow and dilate sufficiently for haemodialysis and were therefore considered to be essentially failed. The impedance moduli from 0 to 10 Hz as well as the average impedance modulus of successful fistulae were significantly lower than those of fistulae that subsequently failed. An attempt was made to locate the presence of reflection sites (i.e. stenoses and branches) from the minima in the impedance modulus spectra. Their locations were compared with those of the reflection sites detected by ultrasound 2 weeks after surgery. However, not all reflection sites detected 2 weeks after surgery were located by the impedance method. It is recommended that both preoperative examination and intraoperative haemodynamic measurements be made to improve the accuracy of the assessment.