2007A12 Explain the physiological principles underlying the use of peritoneal dialysis
in a patient with chronic renal failure with this dialysate solution:
Na+ 132mmol/L, Mg2+ 0.5mmol/L, K+ 0mmol/L, Lactate 40mmol/L, Cl- 96mmol/L, glucose 2.5%, Ca2+ 3.5mmol/L.



·         Intro

·         Mechanisms

·         Special additives




·  Exchange between dialysate and blood across a membrane


·  Maintain fluid, electrolyte, acid-base homeostasis

·  Excrete metabolic waste




·  Movement of solute from high concentration to low concentration

o Slow process

·  Modulated by Gibbs-Donnan effect (?)

o Proteins are anionic, membrane-permeable and attract small cations e.g. Na+

o (Not sure how this is relevant)


·  Movement of solvent from low osmolality to high osmolality

o Dialysate 400mOsm and hypertonic (mainly due to glucose)

o Plasma 290mOsm, by definition isotonic

o Osmolarity: number of osmotically active particles per L

§ = 2 x Na+ + urea + glucose

o Tonicity: effect of a solution on cell size (hypertonic -> swelling)

Solvent drag

·  Movement of solute due to bulk flow of solvent

·  May allow movement of a substance against a concentration gradient


Special additives:


·  Metabolized by liver to produce HCO3-

·  i.e. buffer for H+


·  Large amount

·  Can cause hyperglycaemia, obesity, insulin resistance



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