Donor cats

The diagnostic evaluation of a donor cat is similar to that described for the recipient. Specific investigation of urinary tract anatomy and function is performed by using abdominal ultrasonography, excretory urography, or computed tomography angiography.³⁴ Cats positive for anti-Toxoplasma gondii antibodies are no longer used as donors. Ethical concerns have arisen regarding the use of living feline donors for kidney transplantation. In people, the risk of mortality associated with kidney donation is about 0.03%.³⁵ Similar nominal risks have been observed in donor cats undergoing unilateral nephrectomy. In one study, no perioperative deaths were reported, and serum creatinine and urea nitrogen concentrations remained within reference ranges.³⁶ Most transplant programs also require adoption of the donor cat, regardless of the outcome of the recipient.

IMMUNOMODULATION

Table 3 General Immunosuppression Protocol for Feline Kidney Transplant Recipients*

Organ transplant recipients are maintained on lifelong immunosuppressive therapy to prevent rejection of the foreign allograft (Table 3). The most current protocols include combination therapy using microemulsified cyclosporine and prednisone.¹⁶ Some transplant institutions recommend administering cyclosporine for two weeks before surgery to ensure adequate serum trough levels at the time of surgery, thus preventing initiation of a host vs. graft immune response. Cyclosporine is usually administered at 3 to 5 mg/kg given orally every 12 to 24 hours to obtain whole blood trough concentrations of 500 ng/ml for the first month, then 150 to 250 ng/ml for life.^16,38 Immunosuppressive prednisolone therapy is also initiated just before surgery at 0.25 mg/kg given orally every 12 hours, adjusting to once daily after 30 days.^16,38

Multiple agents have been known to alter cyclosporine metabolism by increasing the blood cyclosporine concentration and reducing cyclosporine elimination. A regimen using ketoconazole with cyclosporine allows a significant reduction in the cyclosporine dose in people after kidney transplantation.³⁹ The same drug interaction has been demonstrated in cats.⁴⁰ The benefit is the possibility of once-daily dosing and a lower cost. The disadvantages are the additional pilling requirements and ketoconazole-associated hepatotoxicosis. Comparison studies are still lacking to provide a substantial advantage over the current protocols used.

TRANSPLANT PROCEDURE OVERVIEW

Anesthesia and preoperative management

Anesthesia of patients with end-stage kidney disease is challenging because of altered renal physiology and pharmacokinetics. Chronic kidney disease affects the hematopoietic, cardiovascular, neurologic, metabolic, endocrine, gastrointestinal, pulmonary, and immunologic systems in individual and interrelated ways. Many characteristic metabolic derangements are present in transplant patients including anemia, acidemia, hyperphosphatemia, hypocalcemia, and uremia. Identification of any dysfunction within these body systems should be performed preoperatively so that correction may be attempted if possible.

Preoperative management of the transplant patient includes parenteral fluid diuresis with balanced electrolyte solutions. If treatment with recombinant human erythropoietin and subsequent transplant delay is inappropriate, anemic patients are given blood transfusions to achieve a PCV of > 30% before surgery. Immunosuppressive therapy is continued the day of surgery, as described earlier. Placing a jugular catheter is ideal to monitor hemodynamic parameters before, during, and after surgery.