SIMPLIFIED MEASUREMENT OF INTRA-ACCESS PRESSURE

Normalized intra-access pressure (P-IA), expressed as the access press ure/systemic blood pressure, detects venous outlet stenosis and correl ates with access blood flow. General use of (P-IA) is limited by time, special equipment needs, and cost. We therefore correlated pressure m easurements from the venous drip chamber (P-DC of Fresenius H-machines and from an external transducer, P-tau, for blood flows (BFR) of 0 to 400-500 ml/min. Measurements were conducted 2-3 weeks apart in a coho rt of 33 patients. P-DC = -21 + 1.28 P-tau; P-DC = P-tau = 75 mmHg at BFR = 146 ml/min. The major determinant of P-tau at BFR = 0 was access type and venous outflow problems. The difference between P-tau and P- DC (Delta = offset) was 17 +/- 1 mmHg (range, 2-43); Delta correlated with the height difference between the two sites. Differences in syste mic blood pressure, zero calibration, and hydrostatic pressure account ed for 90% of the variance between replicate measurements of P-DC. Det ection of outlet stenosis was compared by using P-IA calculated from P -tau and from P-DC + 17. Only three of 66 measurements using the latte r produced misclassification, and never on replicate measurements. P-t au and P-DC measurements in 62 additional patients showed a persistent offset of 17 mmHg. The authors conclude that P-DC at BFR = 0 can be u sed to monitor prospectively prosthetic bridge grafts for stenosis as long as the offset for a particular dialysis machine is determined.