Case 3: Access Flow

Poor access flow is a big problem!

55 year old Caucasian male with history of diabetes, hypertension, coronary artery disease, and end stage renal disease secondary to diabetic nephropathy is on hemodialysis three times a week via a dialysis catheter due to previously failed fistulas. His catheter is malfunctioning and providing a Qb of 200ml/min for the last 2 treatments. You are his rounding nephrologist. You schedule him for a catheter exchange through interventional radiology but patient refuses to go any sooner than the following week as he is “tired of all these procedures.” His current dialysis prescription is as follows: Dialyzer D-flux 180 (KoA 1000ml/min), Qd-500ml/min, and a current Qb of 200ml/min with an EDW of 70kg. The renal fellow in the unit is worried about low urea clearance given poor access blood flow and decides that until the catheter is exchanged, he will change him to a larger dialyzer (D-250) with a KoA of 1600ml/min.
Incorrect. Try again.
Correct! The increase is only 3.6%.

Remember:

  • Dialyzer urea clearance (K) is determined by the lowest of the 3 parameters: Qb, KoA and Qd.
  • At low blood flow (Qb <200ml/min), K is linear to the Qb and is flow-limited so a high KoA or a high Qd does not matter.
  • A bigger dialyzer or higher dialysate flow are helpful in improving K at higher Qb (>400ml/min).
  • Review the graph below: