Hemodialysis Kinetics 101 – Youtube videos tutorial course

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  • We conduct DIALYSIS to remove ‘uremic solutes/toxins’ from blood in a patient with kidney failure.
    • Urea is one of the many uremic toxins (>100 identified). It is considered a low molecular weight toxin (molecular weight: 60 Daltons) that is water soluble. Its volume of distribution is the total body water. It is produced by the liver and is also the end product of protein catabolism.
    • It is only mildly toxic by itself. However it is considered an easily measurable surrogate for other small molecular weight uremic toxins.
    • We frequently measure ‘success’ of dialysis in terms of how effectively we clear the patients blood of urea.
    • This is also called urea clearance.
  • Blood is cleared of urea by its movement across the dialysis filter membrane  into the dialysate.
  • This occurs via both diffusion (diffusive clearance) and convection (convective clearance)
  • Hemodialysis removal of urea (urea clearance) during a dialysis session is measured numerically as Kt/V

 

 

 

 

TRANSPORT ACROSS MEMBRANE


Transport of ‘toxins’, electrolytes, and water occurs from blood to dialysate and of electrolytes from dialysate to blood. This occurs via two methods: Diffusion and Convection. In this module, we will focus here only on transport of solutes from blood to dialysate.

Diffusion

Convection

 

 

 

 

 

HIGH EFFICIENCY VS
HIGH FLUX

High Efficiency

High Flux

 Membrane Characteristics

  •  Numerous pores, thin membrane, and high surface area allowing high small molecule (urea) clearance
  • Larger pores allowing better middle molecule (β2 microglobulin) clearance

 General Characteristics

(high diffusive clearance)

  • Dialyzer urea clearance rate (K) is usually >210 mL/min
  • High KoA (determines ‘efficiency’) – KoA urea of the dialyzer is usually > 800-1000 mL/min. Remember that the in vitro KoAprovided by the manufacturer is often 20% higher than in vivo values.
  • Kuf is variable
  • Clearance of middle molecular weight molecules (β2 microglobulin) is variable
(high convective clearance)

  • Kuf (determines ‘flux’) of dialyzer is high (>15-20ml/h/mm Hg)
  • Clearance of middle molecules (β2 microglobulin ) is high (>20ml/min)

Technical Requirements

  • Dialyzer with a high KoA (>800-1000ml/min)
  • High blood flow (≥350 mL/min)
  • High dialysate flow (≥500 mL/min)
  • Bicarbonate dialysate (it is important to use  Bicarbonate-containing dialysate to avoid symptoms associated with acetate intolerance (i.e., nausea, vomiting, headache, hypotension, worsening of metabolic acidosis, and cardiac arrhythmia)
  • Dialyzer with a high Kuf
  • Ultrapure water for dialysis
  • Automated ultrafiltration control is necessary to avoid errors in TMP calculation that can result in massive flux of water across a high flux membrane and hemodynamic instability

More on High Flux Dialysis

  • HEMO study1 did not show a mortality benefit between high flux and low flux dialysis.
  • However, the HEMO study, MPO2 trial, and EGE3 trial showed a survival benefit (especially cardiovascular) in subset of patients with albumin≤4mg/dl, dialysis vintage ≥3.7 years, diabetes or those with an AV fistula.
  • KDOQI Adequacy Work group recommends use of high flux dialyzers routinely as long as appropriate water treatment is available.

Sources:

  1. Eknoyan G, Beck, GJ Cheung AK, et al. Effect of dialysis dose and membrane flux in maintenance hemodialysis. N Engl J Med 2002; 347:2010. Hemodialysis study(HEMO)
  2. Locatelli, martin-Malo, Hannedouche et al. Membrane permeability Outcome (MPO) study group. Effect of membrane permeability on survival of hemodialysis patients. JASN 2009;20(3):645
  3. Asci, Tz, Ozkahya et al. EGE study group. The impact of Membrane permeability and dialysate purity on cardiovascular outcomes.JASN 2013 May;24(6):1014-23 

DIALYZER KUF

 

HIGH EFFICIENCY VS CONVENTIONAL DIALYZERS

CLINICAL PEARLS:

  • Most dialyzers that are currently in use have a KoA between 800-1600ml/min.
  • In order to get maximum benefiit from a high efficiency dialyzer, you need adequate Qb.

 

HUMAN KIDNEY VS DIALYZERS

 

 

Continue at:  https://hemodialysiskinetics.coursepress.yale.edu

 

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