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Pediatric CRRT Terms and Nomenclature

Pediatric CRRT Terms and Nomenclature. Timothy E. Bunchman. How does dialysis work?. Solute clearance is related to Sieving coefficient Molecular weight of the solute Charge of the solute Gradient across the membrane This can be convective or diffusive.

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Pediatric CRRT Terms and Nomenclature

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  1. Pediatric CRRTTerms and Nomenclature Timothy E. Bunchman

  2. How does dialysis work? • Solute clearance is related to • Sieving coefficient • Molecular weight of the solute • Charge of the solute • Gradient across the membrane • This can be convective or diffusive

  3. Solute Molecular Weight and clearance Solute (MW) Convective Coefficient Diffusion Coefficient Urea (60) 1.01 ± 0.05 1.01 ± 0.07 Creatinine (113) 1.00 ± 0.09 1.01 ± 0.06 Uric Acid (168) 1.01 ± 0.04 0.97 ± 0.04* Vancomycin (1448) 0.84 ± 0.10 0.74 ± 0.04** Cytokines (large) adsorbed minimal clearance *P<0.05 **P<0.01

  4. Definitions and Terms • CVVH/CAVH • Convective clearance • Replacement Solutions • Physiologic sterile solution that is either infused pre filter (NA) or post filter (outside of NA) that infused at a set rate (Qr)

  5. CAVH/CVVH: Convective Clearance

  6. Convective (CAVH/CVVH) Sterile Replacement fluid infused into blood (Qr) Blood Flow (Qb) → → → → → → → → → → → → BUN 70 mg/dl, K 7 meq/dl, Na 140 meq/d ----↓------------------↓----------------------↓------- (ultrafiltrate space) Semi-permeable membrane Ultrafiltrate (Qef) contains BUN and K of ~ 90% of what was in blood and Na of 140)

  7. Definitions and Terms • CVVHD/CAVHD • Diffusive clearance • Dialysate • Physiologic sterile solution that is infused countercurrent to the blood flow rate (Qd)

  8. CAVHD/CVVHDDiffusive Clearance

  9. Diffusive (CAVHD/CVVHD) Blood Flow (Qb) → → → → → → → → → → → → → BUN 70 mg/dl, K 7 meq/dl, Na 140 meq/d ----↓------------------↓--------------------------↕--- Bun 0 mg/dl, K 0 meq/dl, Na 140 meq/dl ← ← ← ← ← ← ← ← ← ← ← ← ← ← ← Dialysis Flow (Qd) Semi-permeable membrane Ultrafiltrate (Qef) contains BUN and K of ~ 90% of what was in blood and Na of 140)

  10. Definitions and Terms • CVVHDF/CAVHDF • Convective clearance • Replacement Solutions • Diffusive clearance • Dialysis solution

  11. CAVHDF/CVVHDFConvective and Diffusive Clearance

  12. Convective & Diffusive (CAVHDF/CVVHDF) Sterile Replacement fluid infused into blood (Qr) Blood Flow (Qb) → → → → → → → → → → → → → BUN 70 mg/dl, K 7 meq/dl, Na 140 meq/d ----↓------------------↓--------------------------↕--- Bun 0 mg/dl, K 0 meq/dl, Na 140 meq/dl ← ← ← ← ← ← ← ← ← ← ← ← ← ← ← Dialysis Flow (Qd) Semi-permeable membrane Ultrafiltrate (Qef) contains BUN and K of ~ 90% of what was in blood and Na of 140)

  13. Definitions and Terms • SCUF (surgeons can’t understand fluid) • Slow continuous ultrafiltration (UF) ultrafiltrate (water and solute) come across the membrane at a rate based upon TMP • Transmembrane pressure (TMP) • The pressure difference between the blood side and the ultrafiltrate side of the membrane • Greater the TMP the greater the UF rate

  14. SCUF Blood Flow (Qb) → → → → → → → → → → → → → BUN 70 mg/dl, K 7 meq/dl, Na 140 meq/d ----↓------------------↓---------------------↓-------- Semi-permeable membrane Ultrafiltrate (Qef) contains solute based upon sieving coefficient

  15. TMP Blood TMP = 0 100 100 100 -------------------O--------↓----------------O-----------↑- Uf TMP = 0 0 100 200 Net TMP 0 100 0 - 100 Semi-permeable membrane

  16. Adsorption • Concept when solute (e.g. plasma proteins) adhere or get adsorbed to a membrane • Commonly discussed with column plasma-adsorption or the “clearance” of cytokines during SIRS

  17. Adsorption Blood Flow (Qb) → → → → → → → → → → → → → Cytokines seen in SIRS ↓ ↓ ↓ ------------------------------------------------------- Semi-permeable membrane with cytokines adherent

  18. Terms and NomenclatureConclusion • Terminology is confusing and often redundant • www.adqi.net paper on Definitions by • Gibney, Kimmel and Lazarus

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