OS214 20051208 Grp4b Dialysis

GROUP 4B

Outline: I. II. III. IV.

V. VI. VII.

DR. ROBERTO TANCHANCO, DECEMBER 8, 2005

EXCRETORY

Objectives Criteria for Dialysis Types of Dialysis: Hemodialysis and Peritoneal Dialysis Physiologic Principles a. Diffusion b. Ultrafiltration c. Urea Kinetic Modeling Indications for Dialysis Complications of Dialysis Hemodialysis vs Peritoneal Dialysis

Objectives • Know the physiologic principles underlying the process of dialysis • Know the indications for the initiation of dialysis • Discuss the impact of dialysis on survival and quality of life in patients with renal failure • Discuss and differentiate between the various modes of dialysis • Be familiar with the complications of dialysis. • Discuss the socioeconomic implications of dialysis therapy Criteria for Dialysis 1. Hyperkalemia 2. Unresponsive to conservative measures 3. Extracellular volume expansion 4. Acidosis refractory to medical therapy 5. Bleeding diathesis 6. Creatinine clearance of 10 mL/min per 1.73 m2 Physiologic Principles • Diffusion • Ultrafiltration • Urea Kinetic Modeling Diagram of Dialysis:

being more widely used due to greater biocompatibility -reuse of dialyzer reduces complement activation 2. Composition and delivery of dialysate- buffer is usually bicarbonate 3. Blood delivery system- composed of: a.) Dialysis machine- blood pump, dialysis solution delivery system b.) Dialysis access-fistula, graft or catheter through which blood is obtained for hemodialysis -complications include thrombosis due to intimal hyperplasia, which results to stenosis 2 to 3cm proximal to the venous anastomosis Diffusion • Random molecular motion, involving a semipermeable membrane • Concentration gradient and collision frequency • Molecular weight, speed, and size • Membrane resistance • Membrane itself • The “unstirred” fluid layer •

ESRD Na 134 mEq/L

Dialysis Solution Na 134 mEq/L

K

K

5.9 mEq/L

0 mEq/L

Ca 8 mg/dL

Ca 10 mg/dL

HCO3 16 mEq/L

HCO3 34 mEq/L

Crea 10 mg/dL

Crea

0 mg/dL

BUN 75 mg/dL

BUN

0 mg/dL

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HEMODIALYSIS vs PERITONEAL DIALYSIS HEMODIALYSIS •

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DIALYSIS

OS 214

favored in pts ( > 80kg) with no residual renal function bec. of larger volume of distribution

Components 1. Dialyzer- plastic device with the facility to perfuse blood and dialysate compartments at very high flow rates -dialysis membranes maybe composed of cellulose, substituted cellulose, cellulosynthetic, and synthetic; the latter

Countercurrent flow • Prevents concentration equilibrium

Principle: -mainly due to solute diffusion down a concentration gradient -rate affected by: * magnitude of the concentration gradient * membrane surface area * mass transfer coefficient of the membrane -a function of porosity and thickness of membrane, size of solute molecule, conditions of flow on the two sides of the membrane -maybe due to ultrafiltration, as in the movement of toxic substances such as the urea ( small molecule, 60 Da) -countercurrent flow prevents the concentration equilibrium •

The Clearance Concept:

DIALYSIS

OS 214 GROUP 4B

EXCRETORY

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DR. ROBERTO TANCHANCO, DECEMBER 8, 2005

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The (hypothetical) volume of blood that is being “cleared” of a waste product per minute Ex. Creatinine clearance means the volume of blood being cleared of creatinine, and not the volume of creatinine cleared -Blood water clearance (no need to memorize) Just use blood clearance X 0.894 (shortcut) •

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Clearance: • Inlet BUN = 100 mg/dL • Outlet BUN = 25 mg/dL • = 75% reduction • If BFR (blood flow rate) = 200 mL/min, then 150 mL (200 x 0.75) of blood is being cleared of urea per minute • But urea is only in the plasma component. The fraction of blood that is plasma = 1 - hematocrit • If Hct = 0.30, then plasma = 0.70, and • plasma flow rate = 140 mL/min (200 x 0.70) • RBC flow rate = 60 mL/min (200 x 0.30) • Water flow rate: • Plasma = 140 x 0.93 • RBC = 60 x 0.80 Blood water clearance: • Just use Blood clearance x 0.894 (shortcut). Factors affecting blood water urea clearance: • Blood flow rate • Dialysis solution flow rate • Dialyzer efficiency (KoA) • when BFR & DFR are ∞

WWhat about protein-bound substances? • Cannot pass through the membrane unless “freed” from the protein • Charcoal – used in a special type of dialyzer to adsorb these substances (ex. Removal of certain poisons), but not for routine maintenance hemodialysis Ultrafiltration • Hydrostatic pressure • Transmembrane pressure (TMP mmHg) • Ultrafiltration coefficient (KUf mL/hr/mmHg gradient) • Osmotic force • Membrane acting as a sieve • Smaller solutes pass through by solvent drag • Larger solutes held back • Patients advised to gain only around 1 kg per day (mostly water) between HD sessions • Target dry weight

The Dialyzer Membrane • High Efficiency: • = High KoA • High Flux: • = High Kuf

PERITONEAL DIALYSIS • •

favored in younger pts. bec. of better manual dexterity and greater visual acuity preferred the independence and flexibility of homebased treatment

OS 214 GROUP 4B

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EXCRETORY

DIALYSIS DR. ROBERTO TANCHANCO, DECEMBER 8, 2005

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infusion of 1 to3 L of dextrose containing solution into peritoneal cavity

DIFFUSION • Peritoneal membrane • Fluid film over endothelium • Capillary endothelium • Interstitium • Mesothelium • Fluid film over peritoneal membrane • Pores • Large ( >20 nm: protein) • Small (4-6 nm: urea, crea, Na, K) • Ultra (