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