Page 712 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Hemodialysis and Extracorporeal Blood Purification 699

session. Animals starting hemodialysis with severe uremia to offset the effects of solute accumulation in the
should be approached similarly to those with acute ure- interdialysis interval to maintain predialysis azotemia
mia until the predialysis BUN is less than 100 mg/dL. and TAC within therapeutic guidelines (see Figure 29-2).
Thereafter, high-efficiency dialysis schedules are well Chronic maintenance hemodialysis is an indefinite
tolerated. Chronic dialysis prescriptions have been therapeutic commitment, and efforts must be taken to
derived empirically but should promote a predialysis prevent long-term complications that are not as evident
BUN less than 70 mg/dL, a postdialysis BUN less than during shorter-term treatments. Maintenance of the vas-
10 mg/dL, and a time-averaged BUN less than cular access is paramount, and rigorous attention must be
50 mg/dL. The targeted spKt/V should be greater than paid to ensure that minor infections are resolved, and the
2.0 per session to provide an equivalent renal clearance catheter is protected from physical damage or movement
(EKR) of at least 10% of normal renal function. within the subcutaneous tunnel. Animals supported with
The choice of dialyzer and dialysate composition gener- chronic hemodialysis still must be given standard medical
ally are similar to those for maintenance treatments in therapy to manage the nutritional deficiencies, anemia,
animals with acute uremia. Blood flow rate can be mineral disturbances, acidosis, and hypertension
increased cautiously to 15 to 25 mL/kg/min or the per- associated with end-stage CKD. 59,131 Prolonged survival
formance limits of the vascular access, and dialysis time unmasks features of CKD rarely identified in animals
lengthened to 300 minutes or longer. The temptation managed only with medical therapy. Malnutrition,
to reduce dialysis time with opportunities to use higher hyperkalemia, fluid retention, renal osteodystrophy,
efficiency dialyzers and faster blood and dialysate flow hypercalcemia, and refractory hypertension become
rates should be avoided. Longer treatment times may consistent clinical features and therapeutic challenges.
appear to have limited additional efficiency for urea
removal, but many solutes, including creatinine, phos- SUPPORT FOR RENAL
phate, potassium, and middle-molecular-weight solutes, TRANSPLANTATION
have different kinetic profiles and are slower to dialyze Renal transplantation is a management option for both
or have delayed transference from cellular or sequestered dogs and cats with renal failure when other options for
compartments. 47,50,55,63,101 Effective clearance of these treatment are exhausted and there is no likelihood for
solutes requires longer treatments than would be recovery of renal function. 2,4,17 Hemodialysis frequently
adequate for urea removal. is used as a bridge to renal transplantation to resolve the
Three treatments per week is the traditional uremia and metabolic disturbances contributing to the
schedule for human patients with end-stage CKD and risks of anesthesia and surgery. Hemodialysis expands
is used for animal patients with serum creatinine the pool of animals acceptable for renal transplantation
concentrations greater than 8 mg/dL. A twice-weekly that otherwise would be considered unsuitable and
dialysis schedule has been used for animals with serum unlikely to survive because of the severity of their ure-
creatinine concentrations between 5 mg/dL and 8 mg/ mia. 34,35 Finite periods of dialytic support may be used
dL before starting dialysis therapy, but a twice-weekly for animals with acute kidney injury in which transplanta-
schedule likely represents the minimum recommendation tion provides the most favorable long-term or most cost-
that will be beneficial. Even highly efficient individual effective outcome. The hemodialysis prescription for
treatments performed twice weekly provide only small animals awaiting renal transplantation is predicated on
contributions to the weekly solute clearance required the severity of the uremia and attendant signs as described
for therapeutic adequacy. 47,55,63,64,101 There are finite for acute and chronic kidney disease, but the course of
limits to the efficacy of individual dialysis treatments to dialysis should be as short as possible to minimize devel-
improve the time-averaged solute concentrations of a opment of complications that would jeopardize the suc-
patient. Solute generation and rebound proceed unop- cess or opportunity for transplantation. Any dialysis-
posed by dialysis during the interdialytic period. These associated infection could delay indefinitely or preclude
processes contribute substantially to the cumulative sol- transplantation and must be avoided. Repeated adminis-
ute retention throughout the week and become more sig- tration of blood products may sensitize the recipient,
nificant as the interdialysis interval lengthens.* The making it incompatible with a potential donor. After
limitations of hemodialysis can only be improved with transplantation, hemodialysis frequently is used to man-
more frequent and longer dialysis schedules that impart age acute uremia precipitated by delayed graft function,
greater efficiency to this intermittent clearance technique surgical complications, acute rejection, or pyelonephritis.
{
rather than more intensive dialysis. A twice-weekly dial-
ysis schedule only will be effective if the patient has suffi- USE OF HEMODIALYSIS TO CORRECT
cient residual renal function (i.e., a continuous clearance) DISORDERS OF FLUID BALANCE
Animals with oliguric or anuric AKI have too little excre-
*References 47, 50, 55, 56, 63, 101. tory function to eliminate administered fluids and
{ References 46, 50, 55, 63, 67,101, 171. become subject to life-threatening fluid accumulation. 35