Equine Ruptured Bladder in Neonate – NAVLE Study Guide

Overview and Clinical Importance

Uroperitoneum is the accumulation of urine within the peritoneal cavity, most commonly caused by rupture of the urinary bladder in neonatal foals. This condition represents a true medical emergency requiring rapid diagnosis and intervention. Uroperitoneum occurs in approximately 0.2% to 2.5% of foals presenting to equine hospitals and carries significant morbidity if not promptly recognized and treated.

The urinary bladder is affected in approximately 73.1% of cases, the urachus in 21.6%, and the ureter in 5.2% of cases. Understanding the pathophysiology, clinical presentation, and management of this condition is essential for NAVLE success.

Anatomy and Pathophysiology

Relevant Anatomy

The equine bladder is lined with transitional epithelium and composed of two interwoven layers of smooth muscle. The inner layer is oriented in a circular fashion and the outer longitudinal layer provides structural support. Critically, the dorsal aspect of the bladder lacks the longitudinal muscle layer, making it the weakest point and the most common site of rupture.

In the neonate, the bladder is attached to the umbilical structures: the urachus (connecting bladder apex to umbilicus) and paired umbilical arteries (running along the lateral aspects). After birth, the urachus normally fibroses and becomes the middle (median) ligament of the bladder, while the umbilical arteries become the round ligaments of the bladder.

Key Anatomical Structures

Pathophysiology of Uroperitoneum

When urine leaks into the peritoneal cavity, electrolytes and water rapidly equilibrate across the peritoneal membrane. This leads to the characteristic electrolyte abnormalities:

• Hyperkalemia: Potassium from urine diffuses into plasma; further exacerbated by mare's milk (high K+, low Na+)
• Hyponatremia: Sodium diluted by increased total body water; diffuses into retained urine
• Hypochloremia: Chloride follows sodium to maintain electroneutrality
• Metabolic Acidosis: Results from lactate accumulation due to poor tissue perfusion
• Azotemia: BUN and creatinine from urine are reabsorbed across the peritoneum

Etiology and Risk Factors

Causes of Bladder Rupture

Sex Predisposition

Studies indicate a higher incidence of bladder rupture in male foals (colts) compared to fillies. This is attributed to the narrower pelvis and longer, narrower urethra in males, which may predispose to increased intravesicular pressure during parturition. However, urachal rupture occurs equally in both sexes.

Exam Focus: Remember: Colts = Cystorrhexis (bladder rupture). The longer male urethra creates more back pressure on a full bladder during birth.

Clinical Presentation

Timeline of Clinical Signs

Foals typically appear normal at birth but develop progressive clinical signs within 24-72 hours (most commonly 2-5 days postpartum). The delay occurs because time is required for sufficient urine accumulation and electrolyte equilibration.

Cardinal Clinical Signs

Diagnosis

Diagnostic Approach

Diagnosis is based on history, clinical signs, laboratory findings, and ultrasonography with abdominocentesis (considered the gold standard).

Laboratory Findings

Abdominocentesis - The Key Diagnostic Test

Abdominocentesis reveals large volumes of clear to yellow fluid with a urine-like odor. The definitive diagnostic criterion is:

Note: BUN ratio is less reliable because BUN equilibrates more rapidly across the peritoneum than creatinine.

Ultrasonographic Findings

Transabdominal ultrasonography (5-7.5 MHz transducer) reveals:

• Large volumes of free anechoic (black) fluid - present in 97% of cases
• Small, collapsed, irregularly shaped bladder - visible in approximately 50% of cases
• Bladder wall discontinuity - only visible in 18-40% of cases (do not rely on this to confirm diagnosis)
• Floating loops of small intestine within the fluid

Additional Diagnostic Tests

• Methylene Blue Test: Inject 10 mL methylene blue into bladder via urinary catheter; blue dye in peritoneal fluid within 15 minutes confirms bladder rupture
• ECG: Essential to assess cardiac effects of hyperkalemia (tall peaked T waves, widened QRS, bradycardia, AV blocks)
• IgG Level: Check for failure of passive transfer (common concurrent finding)
• Sepsis Score: Approximately 50% of foals with uroperitoneum have positive sepsis scores

Differential Diagnosis

Treatment

Uroperitoneum is a medical emergency but NOT a surgical emergency. Preoperative stabilization is critical before anesthetic induction.

Preoperative Stabilization

Goals of Stabilization

• Correct hyperkalemia (target K+ less than 5.5 mEq/L before anesthesia)
• Restore intravascular volume
• Correct acid-base disturbances
• Reduce intra-abdominal pressure

Medical Stabilization Protocol

Surgical Treatment

Surgical Approach

The standard approach is ventral midline celiotomy under general anesthesia. In male foals, the prepuce is sutured closed and reflected off midline.

Surgical Steps

• Ventral midline skin incision cranial to umbilicus
• Enter abdomen, collect peritoneal fluid for culture
• Identify and isolate umbilical structures
• Ligate and transect umbilical vein (cranially)
• Ligate and transect umbilical arteries (2-0 absorbable)
• Identify bladder defect (usually dorsocranial)
• Debride necrotic edges if necessary
• Close bladder in TWO LAYERS using inverting pattern (Cushing or Lembert)
• Test closure with saline + methylene blue via urinary catheter
• Lavage abdomen with sterile saline
• Routine abdominal wall closure

Suture Selection

Postoperative Care

• Continue IV fluid therapy until electrolytes normalize
• Maintain indwelling urinary catheter for 48-72 hours
• Monitor for normal urination post-catheter removal
• Broad-spectrum antibiotics for 5-7 days
• NSAIDs for pain management
• Serial CBC and chemistry panels to monitor recovery
• Postoperative ultrasound to confirm no recurrence

Prognosis and Complications

Survival Rates

Complications

• Recurrence of uroperitoneum (12-20%): Most common complication; due to suture dehiscence or incomplete closure
• Peritonitis: Chemical from urine or septic if concurrent infection
• Abdominal adhesions: Less common than with intestinal surgery
• Incisional complications: Infection, hernia, dehiscence
• Cystic calculi: If suture enters bladder lumen or non-absorbable suture used
• Anesthetic complications: Cardiac arrhythmias from residual hyperkalemia

Exam Focus: The most common complication is recurrence of uroperitoneum (12-20% of cases). This usually manifests 12-264 hours postoperatively. Postoperative ultrasound monitoring is recommended.

Memory Aid