Renal Replacement Therapy Research Paper

Different modes of renal replacement therapy

Renal replacement therapy (aka dialysis) is often required in patient with acute or chronic kidney disease (CKD) to facilitate the removal of undesirable waste products from the body. In the US more than 10% (more than 20 million) of adults may have CKD.1 Chances of having CKD increase after age 50 yrs and is most common among adults older than 70 yrs. Approximately 5%-6% Intensive care unit (ICU) patients have acute renal failure during their ICU stay.2

There are several factors that determine when it is appropriate to initiate dialysis in a patient, however, the primary factor for CKD patients is a Glomerular Filtration Rate (GFR) < 15ml/min/1.73m2. Other factors include uremia, hyperkalemia, inability

This can be accomplished by following mechanisms: 3

1) Diffusion: solutes are moved by a concentration gradient from higher to lower concentration.

2) Ultra filtration: water moves by osmotic pressure; the pressure gradient is known as the transmembrane pressure gradient and is the difference between plasma osmotic pressure and hydrostatic pressure. Determinants of the ultrafiltration rate include the membrane surface area, water permeability of the membrane, and transmembrane pressure gradient.

3) Convection: water moves by transmembrane pressure gradient (similar to ultrafiltration) but solutes are “dragged” along with water. Both large molecular weight (inulin, β2-microglobulin, TNF and vitamin B12) and small molecular weight (BUN, creatinine, and K+) can be moved. When the ultrafiltration rate is increased to provide convection clearance of solutes, this is known as hemofiltration.

Renal replacement therapies - chronic kidney disease

For patient with CKD, there are 2 primary modes of dialysis: hemodialysis or peritoneal

Hemofiltration:

• In CVVH, the filter pore size is larger than HD allowing drug molecules up to 20,000 Da to pass through membrane.

Water/lipid solubility Drugs with that are lipid soluble will tend to remain in the blood whereas high water soluble drugs will tend to partition in water based dialysis fluid.

Plasma protein binding Drugs that are bound to proteins are too large to pass whereas unbound drugs are able to pass through the semipermeable membrane

Volume of distribution (Vd) Large Vd drugs are not easy to eliminate because they are mainly located at tissue binding sites and only small percentage of total drug is removed from the blood after dialysis, re-equilibration between tissue and blood may occur resulting in higher serum concentrations of the drug.

There are also specific dosing recommendations for HD that are at times very different than those for renal dysfunction in patients not on HD and table below have few examples of these kind of dosing.

Drugs Usual dose Dosage adjustment HD dosage adjustment

Acyclovir 5-10mg/kg IV q8h Crcl 25 - 50 5-10mg/kg IV