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Pediatric CRRT Terms and Nomenclature Timothy E. Bunchman
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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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Solute Molecular Weight and clearance Solute (MW)Convective Coefficient Diffusion Coefficient Urea (60)1.01 ± 0.051.01 ± 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)adsorbedminimal clearance *P<0.05 **P<0.01
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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)
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CAVH/CVVH: Convective Clearance
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Blood Flow (Qb) BUN 70 mg/dl, K 7 meq/dl, Na 140 meq/d ---- ------------------ ---------------------- ------- (ultrafiltrate space) Convective (CAVH/CVVH) Semi-permeable membrane Sterile Replacement fluid infused into blood (Qr) Ultrafiltrate (Qef) contains BUN and K of ~ 90% of what was in blood and Na of 140)
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Definitions and Terms CVVHD/CAVHD Diffusive clearance Dialysate Physiologic sterile solution that is infused countercurrent to the blood flow rate (Qd)
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CAVHD/CVVHD Diffusive Clearance
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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) Diffusive (CAVHD/CVVHD) Semi-permeable membrane Ultrafiltrate (Qef) contains BUN and K of ~ 90% of what was in blood and Na of 140)
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Definitions and Terms CVVHDF/CAVHDF Convective clearance Replacement Solutions Diffusive clearance Dialysis solution
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CAVHDF/CVVHDF Convective and Diffusive Clearance
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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) Convective & Diffusive (CAVHDF/CVVHDF) Semi-permeable membrane Ultrafiltrate (Qef) contains BUN and K of ~ 90% of what was in blood and Na of 140) Sterile Replacement fluid infused into blood (Qr)
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Definitions and Terms SCUF (surgeons cant 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
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Blood Flow (Qb) BUN 70 mg/dl, K 7 meq/dl, Na 140 meq/d ---- ------------------ --------------------- -------- SCUF Semi-permeable membrane Ultrafiltrate (Qef) contains solute based upon sieving coefficient
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Blood TMP = 0100100100 -------------------O-------- ----------------O----------- - Uf TMP = 0 0 100200 Net TMP0 100 0 - 100 TMP Semi-permeable membrane
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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
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Blood Flow (Qb) Cytokines seen in SIRS ------------------------------------------------------- Adsorption Semi-permeable membrane with cytokines adherent
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Terms and Nomenclature Conclusion Terminology is confusing and often redundant www.adqi.net paper on Definitions by www.adqi.net Gibney, Kimmel and Lazarus
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