In addition, inter-observer variability in measurement of Doppler flow reduces the reliability of Doppler flow measurement. Magnetic resonance flow is accurate but expensive. Both Doppler flow and magnetic resonance are difficult to perform during dialysis sessions. The Work Group expects that, as technology improves, on-line access flow measurements using dilution technology will become more clinically applicable, and could supplant all other techniques by permitting accurate and inexpensive repetitive measurements at monthly intervals. The Work Group believes that the value of routine use of any technique for detecting anatomic stenosis without concomitant measurement of access flow, venous pressure, recirculation, or other physiologic parameter has not been established.
Prospective monitoring using dynamic or static venous dialysis pressures detects outflow stenoses.
Both methods have acceptable sensitivity and specificity, are inexpensive, and are readily available. Measuring venous pressure is the least expensive method of monitoring for stenosis. A protocol is provided in Table III-3. Shortcomings of venous pressure techniques are the need to standardize for blood tubing, needle size, and hemodialysis machine. The Work Group believes that measurement of static pressure every 2 weeks is the maximum frequency feasible with current hemodialysis staffing patterns.