Pediatric CRRTTerms 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

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

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)

CAVH/CVVH: Convective Clearance

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)

Definitions and Terms

CVVHD/CAVHD Diffusive clearance Dialysate

Physiologic sterile solution that is infused countercurrent to the blood flow rate (Qd)

CAVHD/CVVHDDiffusive Clearance

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)

Definitions and Terms

CVVHDF/CAVHDF Convective clearance

Replacement Solutions Diffusive clearance

Dialysis solution

CAVHDF/CVVHDFConvective and Diffusive

Clearance

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)

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

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

Blood TMP = 0 100 100 100-------------------O--------↓----------------O-----------↑-

Uf TMP = 0 0 100 200

Net TMP 0 100 0 - 100

TMP

Semi-permeable membrane

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

Blood Flow (Qb) → → → → → → → → → → → → →

Cytokines seen in SIRS ↓ ↓ ↓-------------------------------------------------------

Adsorption

Semi-permeable membrane with cytokines adherent

Terms and NomenclatureConclusion

Terminology is confusing and often redundant

www.adqi.net paper on Definitions by Gibney, Kimmel and Lazarus