Improved measurement of vascular access pressure

Vascular access stenosis and thrombosis is one of the key problems for hemodialysis patients. Prospective monitoring of static venous dialysis pressures can be applied to detect outflow stenoses in a vascular access. However, the location of stenoses within the access may influence the diagnostic value of venous pressure measurements. Whereas a decrease in access flow occurs with all types of stenosis, strictures within the arterial anastomosis or between arterial and venous dialysis needle cannot be detected with venous pressure measurements alone. A new approach is discussed, which bases on the improved measurement of static venous and arterial extracorporeal pressures. Extracorporeal pressure at zero blood flow depends on both the position of the heart relative to the extracorporeal blood circuit and the vertical offset between access site and fluid level in the bloodline. After hydrostatic correction of each pressure signal the normalized arterial and venous intra-access pressure ratio AP/MAP can be calculated. A venous stenosis leads to an increase in both arterial and venous pressure ratio. In case of access stenosis between arterial and venous needle the ratio of venous pressure to mean arterial pressure is normal, and only the arterial pressure ratio is elevated. In summary, a combination of arterial and venous pressure measurement is more sensitive and allows differentiation between mid-access and venous stenosis. Hydrostatic correction of the dialysis pressure signal is inevitable. To minimize the rate of access thrombosis, venous and arterial intra-access pressure should be considered when evaluating dialysis pressures as part of any access monitoring program.