Chronic Kidney Disease

Chronic Kidney Disease (CKD) in Dogs and Cats: Pathophysiology, Classification, Prognosis, and Anesthetic Considerations

Pathophysiology of CKD #

Chronic kidney disease (CKD) in dogs and cats is a progressive and irreversible loss of renal function characterized by nephron damage and fibrosis. CKD results from various etiologies, including congenital defects, glomerulonephritis, interstitial nephritis, nephrotoxins, and secondary effects from systemic diseases such as hypertension or diabetes mellitus.

Mechanisms of Disease Progression #

1. Nephron Loss: Damage to nephrons leads to compensatory hyperfiltration in remaining nephrons, which increases intraglomerular pressure and accelerates sclerosis.
2. Fibrosis and Inflammation: Progressive fibrosis occurs due to chronic inflammation, leading to further loss of functional nephrons.
3. Tubular Dysfunction: Impaired tubular function results in decreased concentrating ability (polyuria and polydipsia) and loss of essential electrolytes.
4. Metabolic and Endocrine Disruptions: CKD affects calcium-phosphorus metabolism, leading to renal secondary hyperparathyroidism and systemic complications such as osteodystrophy.
5. Hypertension and Cardiovascular Impact: Systemic hypertension often develops, worsening glomerular injury and contributing to cardiac dysfunction.

IRIS Classification System #

The International Renal Interest Society (IRIS) classifies CKD into four stages based on serum creatinine and symmetric dimethylarginine (SDMA) concentrations:

IRIS Stage	Dogs (Creatinine mg/dL)	Cats (Creatinine mg/dL)	Clinical Signs
Stage 1	<1.4	<1.6	No azotemia, possible early markers like proteinuria or dilute urine
Stage 2	1.4 – 2.8	1.6 – 2.8	Mild azotemia, PU/PD possible but few clinical signs
Stage 3	2.9 – 5.0	2.9 – 5.0	Moderate azotemia, weight loss, decreased appetite, lethargy
Stage 4	>5.0	>5.0	Severe azotemia, uremia, dehydration, vomiting, metabolic imbalances

IRIS also includes sub-staging based on proteinuria (UPC ratio) and systemic blood pressure, which are critical factors in disease progression and therapeutic decisions.

Prognosis and Species Differences #

The prognosis for CKD varies depending on the stage at diagnosis, underlying cause, and response to management. Differences between dogs and cats include:

• Dogs: Generally have a more rapid disease progression, with a median survival of months to a few years depending on the stage at diagnosis and management effectiveness.
• Cats: Typically progress more slowly than dogs, often living for several years post-diagnosis, particularly in earlier stages with appropriate intervention.
• Response to Treatment: Cats tend to tolerate dietary changes and phosphate binders better than dogs, which can contribute to prolonged survival.
• Hypertension Risk: Dogs are more prone to developing systemic hypertension earlier in CKD progression, necessitating closer monitoring and management.

Anesthetic Considerations #

CKD patients present increased anesthetic risk due to their impaired ability to maintain fluid and electrolyte balance, reduced drug metabolism, and potential cardiovascular instability. Key anesthetic concerns include:

1. Fluid Balance & Perfusion: CKD patients are at risk of both dehydration and fluid overload. Preoperative hydration optimization is crucial.
2. Blood Pressure Management: Hypotension must be carefully avoided; balanced anesthesia with judicious use of IV fluids and vasopressors is essential.
3. Drug Metabolism & Excretion: Many anesthetic agents, including ketamine and NSAIDs, rely on renal clearance and should be used cautiously.
4. Electrolyte Imbalances: Hyperkalemia and metabolic acidosis can complicate anesthetic management and should be corrected preoperatively.
5. Postoperative Monitoring: Close monitoring for delayed recovery, worsening azotemia, and changes in urine output is necessary.

Case Management Strategies #

1. Dietary Modification: Prescription renal diets lower phosphorus and protein while providing omega-3 fatty acids to slow progression.
2. Phosphorus Binders & Calcitriol Therapy: Used to mitigate renal secondary hyperparathyroidism and slow disease progression.
3. Hypertension Control: ACE inhibitors (e.g., benazepril) or calcium channel blockers (e.g., amlodipine) to reduce glomerular hypertension.
4. Anemia Management: Erythropoietin-stimulating agents may be required in later stages.
5. Fluid Therapy: Subcutaneous or IV fluids help maintain hydration and electrolyte balance.
6. Regular Monitoring: Serial creatinine, SDMA, and UPC assessments help guide therapy adjustments.

Conclusion #

CKD is a prevalent and progressive disease in dogs and cats, requiring early diagnosis, appropriate classification, and tailored management. Anesthetic considerations are paramount due to altered drug metabolism, hemodynamic instability, and increased perioperative risks. By integrating IRIS staging with a proactive treatment plan, clinicians can enhance patient quality of life and delay disease progression.