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The Role of Dialysis
Adam E. Eatroff, DVM, DACVIM (SAIM)

ACCESS Specialty Animal Hospitals, Los Angeles, CA, USA

Peritoneal dialysis, intermittent hemodialysis, and clearance and restoration of acid–base and electrolyte
continuous renal replacement therapy are being used in balance. Diffusion occurs when uremic solutes redistrib-
companion animal medicine with increasing frequency ute in solution from areas of higher concentration (blood)
for the treatment of both acute kidney injury and chronic to lower concentration (dialysate). The use of a semiper-
kidney disease. Peritoneal dialysis, intermittent hemodi- meable membrane to separate the dialysate from the
alysis and hemofiltration, and continuous renal replace- blood allows for the restriction of movement of larger
ment therapy (the three modalities are hereafter referred substances (protein and cellular components), while
to as “dialysis,” unless they are discussed as separate smaller substances (uremic toxins) are able to redistribute
entities) are employed with the goals of removing accu- freely through the pores of the membrane. Convection
mulated uremic toxins and fluid and reestablishing physi- utilizes the application of a hydrostatic or osmotic force to
ologic acid–base and electrolyte balance when the kidneys blood to promote fluid (plasma water) movement across a
are damaged to an extent that renders them incapable of membrane. Any substances dissolved in the plasma water
performing these duties. The goal of this chapter is to that are small enough to pass through the pores of the
introduce the reader to the indications, treatment goals, membrane are removed. When the removal of fluid,
complications, and prognostic considerations relevant to rather than solute, is the primary indication for convective
dialysis. A discussion of the technical aspects of each clearance, this modality is referred to as ultrafiltration.
therapeutic modality is beyond the scope of this chapter, Adsorption, which quantitatively contributes the least to
but excellent resources exist for the interested reader. uremic solute removal, occurs when substances adhere to
the membrane due to physiochemical interactions.
Peritoneal dialysis is performed by infusion of a solu-
Dialysis Modalities tion (dialysate) into the peritoneal cavity. The peritoneal
membrane serves as a membrane across which uremic
Renal replacement therapy is a term used to describe solutes diffuse from the blood into the dialysate; solutes
various treatment modalities designed to perform the (e.g., bicarbonate) of which the patient is deficient can
excretory, regulatory, and, in some cases, synthetic be administered via diffusion from the dialysate across
responsibilities of the kidney. Renal replacement thera- the peritoneal membrane into the patient’s blood.
pies can be classified as intracorporeal (e.g., renal trans- Convective clearance of uremic solutes and excess fluid
plantation, peritoneal dialysis) and extracorporeal (e.g., can be achieved by use of hypertonic dialysate, which
intermittent hemodialysis and hemofiltration, continu- exerts an osmotic force, drawing plasma water across
ous renal replacement therapy). Renal transplantation the peritoneal membrane into the dialysate. Dialysate is
relies on the provision of a donor kidney graft intended intermittently infused and removed from the peritoneal
to perform the function of the native kidneys, and is cavity in cycles during peritoneal dialysis. Intermittent
reserved for cases of end‐stage kidney disease. This hemodialysis and continuous renal replacement rely on
modality is not discussed further here. the movement of blood through fibers composed of a
The remaining modalities are based on the principles of semipermeable membrane housed in a cartridge (dia-
diffusion, convection, and adsorption for uremic solute lyzer for intermittent hemodialysis; filter for continuous

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical