Page 693 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

CHAPTER • 29

Hemodialysis and Extracorporeal

Blood Purification

Larry D. Cowgill and Thierry Francey

Intermittent hemodialysis is an extracorporeal renal indication in animals in contrast to human therapeutics.
replacement therapy (RRT) used primarily to manage Finite periods of hemodialysis may be prescribed as part
the biochemical and fluid disorders of uremia. Hemodi- of the perioperative management of animals undergoing
alysis was performed first in experimental dogs in renal transplantation. Preoperative dialysis facilitates the
1913 1,57 and now is established as the foundation for surgical candidacy and surgical stability of the patient.
the management of end-stage kidney disease in human Postoperatively, hemodialysis is used in the management
patients. 78 Hemodialysis has been described in dogs for of delayed graft function, acute rejection, surgical
nearly this same period, but only recently has it complications, or pyelonephritis to support the animal
transitioned from clinical obscurity to the advanced until the episode has resolved. Extracorporeal therapies,
standard for the management of acute renal failure in including hemodialysis or hemoperfusion, alone or in
dogs and cats. 34,38,59,96 The demand for hemodialysis combination can be used to clear toxins and toxic
in veterinary therapeutics has expanded rapidly in the past metabolites from animals after accidental poisoning
10 years, and today hemodialysis facilities have been or drug overdose. 34,148,161,185 The use of extracorporeal
established throughout the United States as well as in therapies for toxin removal is gaining greater recognition
Brazil, India, Israel, Italy, Switzerland, Thailand, as an important extension of extracorporeal techniques in
Portugal, and Japan for applications in companion veterinary therapeutics.
animals. The dog and cat equally share the demand
and use of therapeutic hemodialysis, and extracorporeal PHYSICAL PRINCIPLES OF
techniques and equipment for the delivery of hemodial- HEMODIALYSIS
ysis are safe and effective for animals as small as 1.5 kg
and or as large as 600 kg. Diverse creatures from tortoises Dialytic therapies alter the composition of body fluids by
and rabbits to sheep and horses have been managed with exposing blood to a contrived solution, the dialysate,
creative modifications of the procedures and equipment across an interposed semipermeable membrane. The mass
devised for human application. 37 transfer of solute and water occurs by diffusive and con-
The primary therapeutic application for extracorporeal vective forces across the membrane, and the magnitude of
therapies in animals is for the supportive management of the exchange is predicated on the chemical and physical
uremia as a renal replacement therapy (Box 29-1). No characteristics of the solute and the ultrastructure of
conventional medical therapies can reproduce the efficacy the porous membrane. Water and low-molecular-weight
of extracorporeal procedures for correction of the cumu- solutes (<500 Da) pass readily through the membrane
lative biochemical, acid-base, endocrine, and fluid pores, but the movement of larger solutes, plasma
disorders associated with kidney failure. Acute kidney proteins, and the cellular components of blood are
injury is the most common indication for intermittent restricted by pore size and physical characteristics of the
hemodialysis in dogs and cats. Delay in instituting dialysis membrane.
leads to greater uremic symptomatology, morbidity, and Diffusive transfer (dialysis) occurs by the thermal
recruitment of additional organ dysfunction. 34,37,59 motion of the molecules in each solution (blood and
Indefinite use of intermittent hemodialysis in animals dialysate), causing their random encounter with the
with chronic kidney disease is equally indicated, but cost membrane and subsequent transfer through porous
and logistic realities have limited its routine use for this channels of the appropriate size. These random events

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