Chronic_renal_failure

Learning Outcomes

• Understand and recognize the various causes and risk factors associated with chronic kidney disease (CKD) in horses.

• Familiarize with the comprehensive diagnosis, management strategies, and treatment options available for CKD.

Chronic Kidney Disease Overview

• Definition: CKD is defined as a chronic, irreversible, and progressive disease that significantly affects kidney function over time.

• Objective: The condition persists for over three months, leading to notable alterations in the kidneys' structural and functional capabilities.

• Glomerular Filtration Rate (GFR): Generally involves a chronic reduction in GFR, which is essential for assessing kidney performance. The GFR is a key indicator of kidney health, as it indicates how well the kidneys are filtering waste from the blood.

• Diagnosis Challenges: Factors such as assessment protocols and availability of diagnostic tests can influence diagnosis, with a low prevalence noted at referral centers (0.1-0.5%).

• Terminology: It is crucial to differentiate between terms: "failure" indicates end-stage renal failure, while CKD pertains to earlier stages of kidney disease, aligning with definitions in both veterinary and human medicine.

• Nephron Loss: Approximately 70% nephron loss may occur prior to the manifestation of clinical signs, highlighting the insidious nature of this disease. This necessitates regular monitoring and assessment for at-risk horses.

Background and Pathogenesis

• Normal Kidney Function: The kidneys possess dynamic structures that can be impacted by acute and chronic injury processes. Understanding these dynamics is crucial in framing CKD within a broader context of renal health.

• Acute Kidney Injury (AKI) Interaction: Acute kidney injury can initiate either adaptive repair, which may resolve the issue, or maladaptive repair, which results in ongoing damage manifesting as chronic kidney disease. This underscores the importance of early intervention and management of AKI to prevent progression to CKD.

Causes of Chronic Kidney Disease

• Primary Glomerular Disease: Includes conditions like Glomerular Nephritis, where immune complex deposition occurs quietly, often leading to increased impact from pathogens such as Streptococcus spp. and Equine Infectious Anemia Virus.

• Primary Tubulointerstitial Disease: Characterized by chronic interstitial nephritis, primarily triggered by AKI or acute renal failure (ARF) causing nephrotoxicity. This is frequently observed in older horses, highlighting age as a significant factor in disease occurrence.

Clinical Signs of Chronic Kidney Disease

• Common Signs: Presents with a range of non-specific symptoms, including significant weight loss, increased urination (polyuria), and increased thirst (polydipsia), as well as ventral edema.

• Less Common Signs: Other symptoms may include poor appetite, a dull or unkempt hair coat, and the presence of dental tartar, demonstrating associated dental health issues may arise as an indicator of systemic illness.

Clinical Pathology Assessment

• Diagnosis Correlation: Establishing a definitive diagnosis requires a comprehensive correlation of the patient's history, observed clinical signs, and laboratory findings.

  • Increased Creatinine: With creatinine levels being critical, SDMA (symmetric dimethylarginine) is emerging as a noteworthy diagnostic marker for kidney function in equines.

  • Urinalysis Findings: Key findings may include isosthenuria, indicated by a urine specific gravity (USG) of 1.009-1.014, and abnormalities in cellular content like casts, tubular cells, neoplastic cells, and leukocytes.

  • Serum Electrolytes: Frequently observed electrolyte abnormalities include hypercalcemia, hyponatremia, hypochloremia, and hyperkalemia, with variable presentations.

  • Hypoalbuminemia: Often accompanies CKD, along with underlying anemia contributing to the overall clinical picture.

  • Creatinine Changes: It is essential to note that minor fluctuations in creatinine during CKD are generally considered less significant compared to acute conditions.

Imaging and Biopsy Techniques

• Transabdominal Ultrasound: A crucial tool for assessing kidney structure; it can assist in ruling out nephroliths while often yielding normal results. If abnormalities are present, smaller kidney sizes may be observed (normal size generally ranges from 15-18 cm in Thoroughbreds).

• Renal Biopsy Technique: Typically conducted under standing sedation with sterile preparation and local anesthesia. The right kidney is most commonly biopsied due to easier access, although the left may also be viable. Procedures often involve ultrasound guidance for precision. An automated biopsy gun may be applied, but the procedure has complication rates between 10-15% (potential risks include colic or mild hemorrhage, with particular caution advised around the risk of hypertension complicating biopsies due to CKD).

Management Strategies

• Biopsy Outcome-Based Management: Decisions on management are primarily dictated by the findings from biopsies:

  • Treatment for Glomerulonephritis: May include corticosteroids and thorough management of any concurrent bacterial infections, often necessitating antibiotics.

  • Nephrotoxic Agent Avoidance: Critical to evade nephrotoxic medications, including non-steroidal anti-inflammatory drugs (NSAIDs) and certain antibiotics that could exacerbate kidney injury.

• Dietary Management Strategies: Emphasis on balanced protein intake is fundamental, along with a restrictive approach to salt and carbohydrates.

  • Introduction of Vegetable Oil: Suggested to be incrementally introduced at a maximum of 100 ml per day to assist in encouraging diuresis.

  • Water Intake Encouragement: Strategies to enhance water consumption might include the provision of molasses water or specially formulated electrolyte solutions.

Summary of Key Management Principles

• Goal Orientation: The primary aim is to identify and directly address underlying causes, potentially through biopsy results. Additionally, maintaining the horse's appetite and body weight is critical to mitigate the impacts of progressive weight loss.

• Regular Monitoring: Creatinine levels and urine protein-to-creatinine ratio should be routinely reassessed every three months to monitor the disease's progress.

• Prognosis Recognition: Acknowledge the typically poor prognosis associated with long-term CKD, highlighting the necessity to sustain quality of life for the horse and to make informed decisions regarding the timing of euthanasia when quality of life is compromised.