BASIC PRINCIPLES OF DIALYSIS Dr M.ASHRAF CONSULTANT NEPHROLOGIST ARMED FORCES HOSPITAL ALHADA,TAIF

OBJECTIVES • Understand the functions of a normal kidney in relation to artificial kidney •Understand the transport mechanisms of dialysis •Understand the components of the artificial Kidney •Understand the components of dialysate

BASIC PRINCIPLES The kidneys have important roles in maintaining health,when healthy perform the following 1-the kidneys maintain the body's internal equilibrium of water and minerals (sodium, potassium, chloride, calcium, phosphorus, magnesium, sulfat) 2-The acidic metabolism end-products that the body cannot get rid of via respiration are also excreted through the kidneys. 3- function as part of endocrine system ,producing Renin,Erythropoeitin and Calcitriol 3

Function of the kidneys Removal of waste products Urea- breakdown of protein in the diet Creatinine-endproduct of creatine metabolism Skeletal/muscle breakdown

Function of the kidneys(cont) Regulation of • Fluid balance • Electrolyte balance Sodium, potassium, calcium, phosphate, magnesium •Acid/base balance Prevents metabolic acidosis

Endocrine Functio Kidneys (cont) Production of Renin Enzyme that controls blood pressure by affecting Na+ and fluid volume Erythropoietin formation Controls red blood cell production in the bone marrow Stimulates conversion of Vitamin D to its active form –calcitriol –a hormone that enhances absorption of calcium from the enhances absorption of calcium from the intestine

DIALYSIS -Dialysis is an imperfect treatment to replace kidney function because it does not correct the compromised endocrine functions of the kidney. -Dialysis treatments replace some of these functions through diffusion (waste removal) and ultrafiltration (fluid removal)

Dialysis indications Kidney failure - Acute kidney injury - Chronic kidney disease stage 5/ESRD

DIALYSIS Two types 1- Hemodialysis 2- Peritoneal Dialysis

HAEMODIALYSIS

HEMODIALYSIS

PERITONEAL DIALYSIS

PRINCIPLES OF DIALYSIS Dialysis works on the principles of the diffusion of solutes and ultrafiltration of fluid across a semi-permeable membrane. -Diffusion : is a property of substances in water; substances in water tend to move from an area of high concentration to an area of low concentration Fluid removal ultrafiltration: is achieved by altering the hydrostatic pressure of the dialysate compartment, causing free water and some dissolved solutes to move across the membrane along a created pressure gradient. OSMOSIS/Convection : movement of water from low solute concentration to high solute concentration--Haemofiltration

Understanding dialysis To understand Dialysis you must know what kidney functions are replaced by dialysis: –Removal of waste products from the blood –Regulation of fluid balance by removing excess fluid from the blood –Regulation of electrolyte and acid/base balance in the blood

Further understanding dialysis Scientific Principles of dialysis include the following: •Solvents •Solutes •Semipermeable membranes •Transport mechanisms

Solutions •Solutions composed of, –Solvent is a fluid(water) –Solute is a substance that can be dissolved in a solvent Potassium, Sodium and Calcium are examples

Dialysate •Composed of concentrated electrolytes, bicarbonate and treated water - Electrolyte concentration in the dialysate determine what is removed or given to the patient -Tailored to each patients needs based on blood chemistries -Regulates electrolyte and acid/base balance in the blood

Dialysate Enables the removal of • Waste products •Excess fluid Prevents excess removal of •Essential electrolytes •Excessive fluid depletion

Artificial kidney •Also called a dialyzer It contains two compartments: • Blood and dialysate Compartments are separated by a semipermeable membrane •Hollow fibers Compartments are encased in a clear plastic cylinder which acts a support for the fibers

DIALYSER(Artificial kidney)

What is semipermeable membrane? A thin layer of material with pores that allow smaller molecules to pass through but not larger molecules •Blood cells are too large to pass through •Waste products, excess chemicals, and excess fluid can pass through

Transport mechanism Necessary to move fluid and solutes through the semi-permeable membrane •Mechanisms used in dialysis – Osmosis/Convection –Diffusion – Filtration –Ultrafiltration

Osmosis/Convection Movement of FLUID across a semipermeable from an area of LOWER solute concentration to an area of HIGHER solute concentration.

DIFFUSION Movement of dissolved particles (Solutes) across a semipermeable membrane from an HIGHER solute concentration to an area of LOWER solute concentration

Filtration Process of passing fluid through a filter or semipermeable membrane. •Filtration is controlled by hydrostatic pressure. •Fluid always moves from an area of higher pressure to an area of lower pressure •Regulates fluid balance in the blood

Ultafiltration Controlled fluid removal by manipulation of hydrostatic pressure. Ultrafiltration uses both positive and negative pressure: Positive pressure pressure exerted by the blood flowing through the dialyzer, Results from blood being pushed by blood pump Negative pressure pressure applied to the dialysate side by the machine Pulls excess fluid from blood compartment to dialysate compartment drain

Dialysis prescription Contains physician orders for the dialysate necessary to meet the needs for each patient – Calcium, Potassium and Sodium Contains physician orders for the dialyzer necessary to meets the needs for each patient surface area available for dialysis is related to dialyzer size Contains physician orders for a target bodyweight and length of dialysis treatment Contains physician orders for a blood flow rate

QUESTIONS?