42. Chronic renal failure – causes, diagnostic, management

What is chronic renal failure (CRF)?

A gradual decrease of renal function over months to years

What causes the clinical signs of CRF?

The toxic effect of retained products normally excreted by the kidney (urea, nitrogenous products, hormones) and loss of normal products of the kidneys (erythropoietin)

Which animals are typically affected by CRF?

Older animals (>7 years old)

What is azotaemia?

Increased concentration of non-protein nitrogenous waste products, i.e. urea and creatinine, in the blood

What does azotemia indicate?

A loss of at least 75% of renal functional capacity (some sources say 80%)

What is the most common cause of CRF?

Most often idiopathic (unknown)

What are some inherited causes of CRF?

Predisposition in Persian and Abyssinian cats, Bull Terriers, German Shepherds, Cairn Terriers, Samoyeds, and Golden Retrievers

What are some other causes of CRF?

Secondary to

1. Acute renal failure

2. Glomerulonephritis

3. Nephroliths

4. Pyelonephritis

5. Polycystic kidney disease

6. Nephrotoxins (drugs, toxins, metabolites)

7. Amyloidosis

8. Neoplasia

9. Hypercalcaemia

10. Hypokalaemic nephropathy

11. Diabetes mellitus

12. Infections (Leptospirosis, FIP, Rickettsia)

What are some risk factors for CRF?

Aging, hypercalcaemia, hypokalaemia, hypertension, urinary tract infection, and diabetes mellitus

What are some mild clinical signs of CRF?

Poor coat, weight loss, dehydration, lethargy, and PU/PD (cats with mild CRF may be asymptomatic)

What are some moderate clinical signs of CRF?

Nocturia, oral ulceration, uraemic breath, hypertension, anorexia, vomiting, and ptyalism (excessive salivation)

What are some severe clinical signs of CRF?

Seizures, blindness, muscle weakness, and fluid retention

What is uraemic syndrome?

A constellation of clinical signs associated with advanced renal failure, including anaemia, gastrointestinal disturbances, neurological disturbances, osteodystrophy, and metabolic acidosis

What information should be gathered in the history for diagnosing CRF?

1. PU/PD, Anorexia, lethargy, vomiting, weight loss, nocturia, constipation, diarrhoea

2. Acute blindness – because of hypertension. Seizures & coma.

3. Cats: ptyalism & muscle weakness with cervical ventroflexion

What are some physical examination findings in CRF?

Small, irregular kidneys or enlarged kidneys (due to polycystic kidney disease or neoplasia), dehydration, cachexia/poor body condition, mucous membrane pallor, oral ulceration, uraemic breath odour, and constipation

What are some haematological findings in CRF?

Non-regenerative anaemia (due to lack of erythropoietin)

What are some biochemical findings in CRF?

Azotaemia (high BUN and creatinine), hypokalaemia, hyperphosphataemia, and acidosis

What are some urine findings in CRF?

Low urine specific gravity (inability to concentrate urine) and mild proteinuria without inflammatory changes

What are the biomarkers used for evaluation of renal function?

1. Cystatin C

2. SDMA

What is Cystatin C?

An endogenous marker of renal function. Its concentration in blood is stable when kidneys have normal function, and elevated if kidney disease. Very useful in early detection of kidney disease

What is SDMA?

Symmetric DiMethylArginine, a biomarker for kidney function, more sensitive than creatinine

What imaging techniques are used to diagnose CRF?

X-ray (small or large kidneys) and ultrasound (small kidneys and hyperechoic renal cortex (fibrotic))

What are the aims of CRF management?

1. To resolve the clinical signs of uraemia

2. Eliminate risk factors (urinary infection)

3. Correct fluid and electrolyte deficits

4. Maintain body condition

5. Reduce progression of renal failure

What are some treatments for CRF?

1. Fluids, correction of electrolyte and acid-base imbalance (potassium chloride for hypokalaemia)

2. Renal diet (low in protein)

3. Erythropoietin (EPO) injections

4. ACE inhibitors (to control hypertension)

5. Antiemetics, H2 blockers, proton pump inhibitors, and mucosal protectants

What medication is used for uraemic crisis?

Famotidine (decreases stomach acid production and treats peptic ulcers)

How is appetite typically affected in cats with chronic renal failure?

Decreased

What are some key kidney parameters measured in CRF?

Creatinine, urea/BUN, SDMA, and Cystatin C

How is blood affected by chronic kidney disease?

No erythropoietin produced → non-regenerative anaemia

Do patients with CKD get nauseous?

Yes (Tx: maropitant)