Stability of access resistance during haemodialysis

Access blood flow (Qac) is considered a useful indicator in the surveillance of haemodialysis access function. However, changes in Qac may be due to changes in blood pressure and/or to changes in access resistance (AR).

Weekly readings of Qac, cardiac output, and arterial blood pressure measured early and late during haemodialysis were obtained in 11 patients for a period of 3 weeks. Qac was determined from thermodilution of extracorporeal blood returning to the patient with reversed placement of blood lines and by measurement of arterial and venous blood temperatures in the extracorporeal circulation. Data are given as mean +/- SE.

Qac dropped as mean arterial pressure (MAP) and total peripheral resistance (TPR) decreased, but increased when MAP and TPR increased. Linear regressions between the change in access flow and the change in MAP (deltaQac%=0.80*deltaMAP%-1.6, r2=0.39), and the change in TPR (deltaQac%= 0.54*deltaTPR%-9.2, r2=0.35) respectively, were significant (P<0.001). Whereas Qac significantly decreased (-8.4+/-3.3%, P<0.01) during the same treatment, AR remained unchanged (4.7+/-3.2%; P=NS). AR for all studies was 16.5+/-1.0 peripheral resistance units (1 PRU=2.226 kPa min l(-1)). There was a trend for resistance to increase (5.1+/-2.6%, P=NS) and for flow to decrease (-6.1+/-2.3%, P=NS) during the 3 weeks of the study.

Qac measured during haemodialysis is variable and depends on haemodynamics, but AR is constant. AR is related to the physical structure of the peripheral access. Because of its intradialytic stability AR may be better suited as an indicator of access function.