Simplified Measurement of Intra-Access Pressure

Abstract

Normalized intra-access pressure (P_IA), expressed as the access pressure/systemic blood pressure, detects venous outlet stenosis and correlates with access blood flow. General use of (P_IA) is limited by time, special equipment needs, and cost. We therefore correlated pressure measurements from the venous drip chamber (P_DC of Fresenius H-machines and from an external transducer, P_**, for blood flows (BFR) of 0 to 400–500 ml/min. Measurements were conducted 2–3 weeks apart in a cohort of 33 patients. P_DC = −21 + 1.28 P_**; P_DC = P_$$ = 75 mmHg at BFR = 146 ml/min. The major determinant of P_$$, at BFR = 0 was access type and venous outflow problems. The difference between P_$$, and P_DC (δ = offset) was 17 $$ 1 mmHg (range, 2–43); δ correlated with the height difference between the two sites. Differences in systemic blood pressure, zero calibration, and hydrostatic pressure accounted for 90% of the variance between replicate measurements of P_DC. Detection of outlet stenosis was compared by using P_IA calculated from P_$$ and from P_DC +17. Only three of 66 measurements using the latter produced misclassification, and never on replicate measurements. P_$$, 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 used to monitor prospectively prosthetic bridge grafts for stenosis as long as the offset for a particular dialysis machine is determined.