SIMPLIFIED MEASUREMENT OF INTRA-ACCESS PRESSURE

The measurement of intra-access pressure (P-IA) normalized by mean art erial BP (MAP) helps detect venous outlet stenosis and correlates with access blood flow. However, general use of P-IA/MAP is limited by tim e and special equipment costs. Bernoulli's equation relates difference s between P-IA (recorded by an external transducer as P-T) and the ven ous drip chamber pressure, P-DC; at zero flow, the difference in heigh t (Delta H) between the measuring sites and fluid density determines t he pressure Delta P-H = P-IA - P-DC. Therefore, P-DC and P-T measureme nts were correlated at six different dialysis units, each using one of three different dialysis delivery systems machines. Both dynamic (i.e ., with blood flow) and static pressures were measured. Changes in mea n BP, zero calibration errors, and hydrostatic height between the tran sducer and drip chamber accounted for 90% of the variance in P-DC, wit h Delta P-H = -1.6 + 0.74 Delta H (r = 0.88, P < 0.001). The major det erminants of static P-IA/MAP were access type and venous outflow abnor malities, In grafts, flow averaged 555 +/- 45 ml/min for P-IA/MAP > 0. 5 and 1229 +/- 112 ml/min for P-IA/MAP < 0.5. Delta P-H varied from 9. 4 to 17.4 mmHg among the six centers and was related to Delta H betwee n the drip chamber and the armrest of the dialysis chair, Concordance between values of P-IA/MAP calculated from P-T and from P-DC + Delta P -H was excellent. It is concluded that static P-DC measurements correc ted by an appropriate Delta P-H can be used to prospectively monitor h emodialysis access grafts for stenosis.