A Case A Week for Veterinarians: Solution for case 24

Tentative diagnosis: Azotemia due to chronic renal failure (CRF).

Further diagnostic tests:
* Abdominal radiography/ultrasound to demonstrate decreased size of kidneys.

* Urine creatinine:protein ratio.

* Renal biopsy (not commonly performed).

* Blood pressure to demonstrate hypertension.

Isosthenuria is a common finding in chronic renal failure when two thirds of the functioning nephrons are lost.

Azotemia is seen when at least three fourths of the functioning nephrons are lost. Azotemia presents with increased BUN, creatinine, GI, and neurological clinical signs. This patient’s presentation would suggest that she has lost at least three fourths of her functioning nephrons.

Predisposing factors for CRF are age, chronic obstruction, infection, heart failure, and tubular disease. A urine sample taken from this patient, via a cystocentesis, ruled out bacterial infection. Patient’s heart sounded normal on auscultation. The renal failure was attributed to her age.

Management of chronic renal failure is a multifactor process. Most importantly hydration and electrolytes must be maintained with in normal limits. An appropriate renal diet will be low in protein, phosphorous, and sodium. Some other factors which must be addressed in the management of chronic renal failure include anemia, proteinuria, and gastrointestinal processes.

Anemia is due to decreased production of erythropoietin by renal peritubular cells. The anemia could also be from blood loss via GI ulcers, or iatrogenic from blood draws. The anemia is non-regenerative normochromic normocytic.

Treatment of anemia with erythropoietin (EPO) is indicated when the PCV falls below 18% and the patient is showing clinical signs of anemia/hypoxia. Caution must be used with EPO since it is of human origin. Dogs can produce antibodies against it. In severe anemia requiring immediate relief of clinical signs a blood transfusion can be done.

Proteinurea is seen because glomeruli have been damaged enough to allow loss of protein and anti-thrombin III. This decreases oncotic pressure, leading to edema. The loss of anti-thrombin III causes coagulation issues. Many of these patients have pulmonary thromboembolism as a complication.

These patients can be treated with angiotensin converting enzyme inhibitors which decreases the pressure in the glomeruli by dilating the efferent renal artery. This decrease in pressure helps prevent loss of proteins into the urine. Canine patients with CRF and proteinuria tend to have a decreased survival.

GI ulcers and nausea and vomiting are the common clinical signs seen. Uremic toxins activate the chemoreceptor trigger zone which leads to the nausea and vomiting. These uremic toxins also increase gastrin production which increases hydrochloric acid production in the stomach, leading to GI ulcers.

These complications are treated by decreasing the uremic toxins via hydration; protecting the stomach by decreasing acid production, and controlling the nausea and vomiting by blocking the chemoreceptor trigger zone. Acid production can be decreased using histamine blockers or proton pump inhibitors. Sucralfate can be used to protect/coat ulcers. The nausea can be controlled with medication targeted at dopamine antagonism, serotonin, or neurokinin.

Treatment: