Blood flow rate: an important determinant of urea clearance and delivered Kt/V

Implementation of the Dialysis Outcomes Quality Initiative (DOQI) Guidelines for hemodialysis adequacy will necessitate an increase in delivered Kt/V for many patients. Before increasing Kt/V by prolonging the patient's treatment time, it is important to verify that the prescribed dialyzer urea clearance is being achieved. The principal determinant of dialyzer urea clearance is blood flow rate. Actual blood flow rates are frequently less than the nominal blood flow rate displayed by the dialysis machine, particularly at higher flow rates, leading to lower than expected urea clearances. The major reason for the reduction in blood flow rate is a low pressure in the arterial blood line proximal to the blood pump. This effect can be mitigated by the use of large bore access needles. For quality assurance purposes, actual blood flow rates should be determined by correcting nominal blood flow rates for pressure effects using empirical relationships or by using an ultrasonic flow meter. Because a poorly functioning blood access may further reduce the effective blood flow rate, blood access performance should also be monitored regularly.