Category Archives: Clinical Application

Clinical Application

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Clinical Application

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.

Clinical Application

Case 7: Dialysis Related Amyloidosis

“Ouch my wrist hurts.” Your nephrologist may be able to help.

You see an 82 year old African American male with history of ESRD secondary to polycystic kidney disease, who has been on hemodialysis for the last 12 years via a left brachiocephalic AVF. He is otherwise in surprisingly good health and very functional. While you are rounding in the dialysis unit, he tells you that he has been having left shoulder and left wrist pain and was told that he may have carpal tunnel syndrome in his left wrist. You are concerned that he may be developing dialysis related amyloidosis.

Clinical Application

Case 6: Access Recirculation

Round and round we go! A case of access recirculation.

You see a 72 year Asian male with history of diabetes, hypertension, and ESRD on HD via a left radio-cephalic AVF while rounding in your dialysis unit. His dialysis Rx is a dialyzer D flux 250, Qb of 400ml/min, Qd- 600 ml/min for a duration of 4 hours. His Kt/V on three times a week hemodialysis has ranged between 1.6-1.8. Your dialysis unit nurse reports that most recently checked Kt/V has dropped down to 1.0 confirmed on 2 different checks. He has been compliant with his dialysis treatments and has completed the full 4 hours as prescribed. Patient feels fine. His physical exam is unremarkable with blood pressures ranging between 130-150 systolic and trace edema.

Clinical Application

Case 5: Dialysis Disequilibrium Syndrome

 Lets slow things down! A patient at risk of dialysis disequilibrium syndrome

58 year old Caucasian female with history of systemic lupus erythematosus, hypertension, stroke, alcoholic cirrhosis and chronic kidney stage 5 is being initiated on hemodialysis for worsening uremic symptoms (worsening nausea, vomiting and headaches over the past couple of months) via a left arm brachiocephalic AV fistula. Her predialysis laboratory data is as follows: BUN- 140mg/dl; creatinine- 8.0; Serum K- 5.2meq/l; serum bicarbonate-12meq/l. Serum Na-135meq/l.

Choose the best dialysis Rx for this patient for his first hemodialysis treatment.

Clinical Application

Case 4: Dialyzer Size

Is a bigger dialyzer, a better dialyzer?

You are the Medical director of a dialysis unit. A dialyzer manufacturing company is trying to sell you high efficiency dialyzers with a KoA of 2000ml/min. You are currently using dialyzers with a KoA of 1000ml/min.

Clinical Application

Case 2: Constrained T

Not a minute more than 3.5 hours!

67 year old African American male with history of diabetes, hypertension and advanced chronic kidney disease has been initiated on dialysis in the hospital. He has received 6 treatments so far and has done well without significant issues with hypotension or cramping. He will now be transitioning to your outpatient dialysis unit. The patient weighs 70kg and has a well functioning AV fistula. You have done your smart calculations (Case 1) and know that he needs to be dialyzed for 3.9 hours for a goal sp Kt/V of 1.4. However, the patient is adamant that he will not stay for more than 3.5 hours because that’s what his friend does. How would you calculate the initial dialysis prescription now?

STEP 1: Start with T since it it a non-negotiable for the patient
T = 3.5 hours or 210 min

STEP 2: Calculate your V
V = 60% of 70kg = 42L or 42,000 ml

STEP 3: Remember your goal spKt/V
spKt/V = 1.4

STEP 4: Do the math
1.4 x 42,000ml / 210min = 280ml/min

STEP 5: Assume that you would like to prescribe a Qb of 400ml/min and a Qd of 500ml/min

STEP 6: Select different KoA options to see what range your KoA should be to reach at goal spKt/V of 1.4

Clinical Application

Case 1: Dialysis Prescription

Calculate an initial dialysis prescription (Rx), based on goal spKt/V

67 year old African American male with history of diabetes, hypertension, and advanced chronic kidney disease has been initiated on dialysis in the hospital. He has received 6 treatments so far and has done well without significant issues with hypotension or cramping. He will now be transitioning to your outpatient dialysis unit. The patient weighs 70kg and has a well functioning AV fistula.
How would you calculate the initial dialysis prescription based on goal spKt/V?

Clinical Application

Playground Debrief

K INCREASES WITH INCREASE IN Qb

CLINICAL PEARLS:

  • Dialyzer blood flow rate is a big determinant of K and ultimately Kt/V. Ideally Qb should be set between 400ml/min to 500ml/min as tolerated. Therefore when aiming for a goal Kt/V, ensure the delivered Qb is adequate.
  • Dialysis catheters tend to allow lower Qb than AVF and AVG.
  • K can NEVER exceed the Qb. If all the blood entering the dialyzer is cleared of urea in a minute, K is Qb.

K INCREASES WITH INCREASE IN Qd, but…

CLINICAL PEARL:

  • Higher Qd increases dialyzer urea clearance (K) but as Qb approaches Qd, K starts to plateau. Therefore, Qd should typically be 1.5-2 times the Qb to maximize diffusive clearance.
  • At a Qb of 400-500 ml/min, a Qd of UP TO 800ml/min makes sense.
  • An increase of Qd from 500ml/min to 800ml/min increases K only by 8-12% when the Qb and KoA are not limiting i.e. a high efficiency dialyzer is used and the Qb >400ml/min (as there is more effective surface area for diffusion).
  • Increasing Qd >800ml/min usually doesn’t add to the K or KT/V as the Qb becomes limiting (shown in graph). Dialystate is expensive, why waste it?
  • Qd of 500-600ml/min is often adequate to achieve target urea clearance with a conventional Qb of 400ml/min
  • An additional lesson is that with daily hemodialysis methodologies that have reduced Qds of 150 mL/min (for example, NxStage) or continuous veno-venous hemodialysis (CVVHD) techniques with Qds of 50–100 mL/min, there is no reason to employ higher Qbs or to use large dialyzers, as K will be limited by Qd.

K INCREASES WITH INCREASE IN KoA

CLINICAL PEARLS:

  • K increases with increasing dialyzer efficiency (KoA)
  • However, the increase in K is most pronounced at adequate pump blood flow.
  • At a Qb of <200ml/min, despite using a high efficiency dialyzer, K is low (the curves start to converge at a K of <170ml/min as shown in the graph).
  • At a Qb of >200ml/min, the curves start to separate and K rises in proportion to the rise in KoA. Rise in K at this point is therefore ‘membrane limited’. Hence, if you want the most benefit out of your high efficiency dialyzer, you need adequate blood flow preferably >400ml/min

Feel free to go back to the playground case to understand how increases in Qb, Qd, and KoA impact K and Kt/V