Table 2.

Methods to measure dynamic, static, and slow-flow venous pressures

Dynamic Venous Dialysis Pressure Monitoring Protocol*
  • Establish a baseline initiating measurements when the access is first used.

  • Measure venous dialysis pressure from the hemodialysis machine at Qb 200 ml/min during the first 2 to 5 min of hemodialysis at every hemodialysis session.

  • Use 15-gauge needles (or establish own protocol for different needle size).

  • Assure that the venous needle is in the lumen of the vessel and not partially occluded by the vessel wall.

  • Pressure must exceed the threshold three times in succession to be significant.

  • Assess at same level relative to hemodialysis machine for all measurements.

Static Venous Pressure Measurement Protocol
  • Turn the blood pump off and clamp tubing between the dialyzer and the venous drip chamber.

  • Make static measurement (P) from venous transducer exactly 30 s after stopping blood flow.

  • Determine in centimeters the height difference between the arm of the chair and blood in the venous drip chamber (H).

  • Calculate estimated intra-access pressure: [eIAP = P + (0.35 × H+ 3.4)]

  • Measure mean arterial pressure (MAP).

  • Calculate eIAP/MAP (absolute eIAP/MAP >0.5 or a progressive rise on repeated measurements indicates a stenosis/thrombosis beyond the venous needle site in AV grafts).

Slow Flow Venous Pressure Measurement Protocol
  • Measure venous pressure from machine transducer at a blood flow of 50 ml/min during first 15 min of dialysis.

  • Measure MAP.

  • Calculate ratio of various pressures and MAP.

  • Investigate any venous pressure/MAP ratio >0.6.

  • * To interpret the dynamic protocol, the clinician must obtain three measurements in succession above the threshold to eliminate the effect of variation caused by needle placement. Hemodialysis machines measure pressure with different monitors and tubing types and lengths. These variables, as well as needle size, influence venous dialysis pressure. The most important variable affecting the dynamic pressure at a blood flow of 200 ml/min is the needle gauge. It is essential to set thresholds for action based on machine manufacturer, tubing type, and needle gauge.