10.23.2025 - SAS

Introduction

Good morning.

Urinary Tract Obstruction and Catheterization Procedures

Trauma during Catheterization

  • The procedure of attempting to move obstructive stones from the urethra into the urinary bladder can cause trauma. This often involves mechanical manipulation that can abrade or lacerate the urethral lining.

  • Trauma can occur especially when forcing a catheter into the urethra, leading to mucosal damage, hemorrhage, or even perforation if excessive force is applied.

  • Some stones are smooth, while others are sharp and irregular. Smooth stones may cause less friction but can still lead to pressure necrosis, while sharp stones can directly incise or tear the urethral wall, potentially causing significant urethral trauma and inflammation.

  • Urethral Diameter: The urethra naturally widens as one moves more proximally into the urinary bladder. This wider diameter in the more cranial urethra usually mitigates significant problems, as stones may pass more easily or a catheter can be advanced with less resistance once past narrower, more distal segments.

  • Encountered problems include urethral perforation while attempting to push stones from the urethra to the bladder. Perforation can lead to extravasation of urine into surrounding tissues, causing severe inflammation, infection, and potential systemic complications.

Hyperkalemia Associated with Urethral Obstruction

  • Definition and significance of hyperkalemia in impacted patients: Hyperkalemia is an electrolyte imbalance characterized by abnormally high levels of potassium in the blood. In cases of urethral obstruction, the body's inability to excretes potassium via urine, exacerbated by potential metabolic acidosis, leads to its accumulation, posing a life-threatening risk due to its effects on cardiac function.

  • Hyperkalemia Levels: Mild hyperkalemia begins just over 5 mEq/L, where some patients may start to show clinical signs such as weakness, lethargy, or electrocardiographic (ECG) changes (e.g., tall T waves, prolonged PR interval).

  • Severe signs can manifest at levels around 6 to 7 mEq/L, or higher (8-10 mEq/L), including severe bradycardia, widened QRS complexes, absent P waves, and ultimately ventricular fibrillation or asystole.

Treatment Approaches

  • Initial Management: Fluids, specifically intravenous crystalloid solutions, are typically the first line of treatment unless severe arrhythmias or urgent situations arise. Fluids help dilute the circulating potassium and promote diuresis once the obstruction is relieved, facilitating renal potassium excretion.

  • If necessary, calcium gluconate can be administered intravenously to directly counteract the cardiotoxic effects of hyperkalemia by stabilizing cardiac cell membranes, thereby reducing the risk of arrhythmias without lowering serum potassium levels.

  • Dextrose with Insulin: Administered to help drive extracellular potassium back into cells. Insulin facilitates the uptake of glucose, and in doing so, it also promotes the intracellular shift of potassium, thereby alleviating hyperkalemia's effects on the extracellular fluid and reducing overall serum potassium levels.

Urethrostomy Procedures in Canines

Pre-Scrotal Urethrostomy

  • Purpose: To create a permanent opening in the urethra, typically to remove stones obstructing the urethra at or caudal to the penis, or to bypass a permanent stricture in this region.

  • Leaving the incision open to heal by second intention (allowing it to close naturally through granulation and epithelialization) may require extended hospitalization due to persistent bleeding and the need for frequent wound care to prevent infection and ensure proper healing.

  • Catheters may be placed for a few days until bleeding stops, helping to divert urine away from the healing incision, stent the urethra, and minimize contamination.

  • Post-operative function: Patients generally continue to urinate through the newly created stoma for a few days before the surrounding tissues begin to swell and closure of the primary skin incision starts.

  • Suturing techniques, involving direct apposition of urethral mucosa to skin, can also be employed to close defects, aiming to achieve primary wound healing. However, this might lead to stricter formation (narrowing of the urethral opening) due to fibrosis and inflammation at the surgical site.

  • Bleeding Risk: Significant bleeding from this area will continue for a time post-operation due to the highly vascular nature of the corpus spongiosum surrounding the urethra.

Suture Techniques

  • Some surgeons opt to suture closed areas to minimize bleeding by providing direct hemostasis and reducing the open surface area, which also shortens hospitalization time. However, this increases the likelihood of strictures, as the inflammatory response to sutures and tissue manipulation can lead to excessive scar tissue formation and subsequent narrowing of the urethral lumen.

Proximal Urethral Obstructions

  • An alternative procedure for more proximal obstructions, perineal urethrostomy (PU), is usually less preferred due to increased surgical difficulty, a higher risk of infection, and significant hemorrhage. This area is anatomically more complex and deeper within the perineum.

  • This area is deeper and has more cavernous tissue (corpus spongiosum) compared to the pre-scrotal region, leading to a much higher risk of significant hemorrhage during and after the procedure, which can be challenging to control.

  • Post-operative complications including stricture formation are generally higher with perineal urethrostomy compared to pre-scrotal approaches, particularly with any suture attempts in this area, due to greater tissue manipulation and inflammatory response.

Surgical Steps

  • The procedure involves incision through the skin, subcutis, and into the urethral tube at the midline of the perineal area. Careful dissection is required to identify and isolate the urethra.

  • Care is taken to mobilize surrounding tissue to avoid creating tension on the suture lines and to ensure direct, everted apposition of urethral mucosa to skin, which is crucial for preventing a stricture.

  • A catheter is typically left in place for healing and urinary diversion to protect the suture site from urine flow, act as a stent to maintain lumen patency, and minimize infection risk during the initial healing phase.

  • Urethra Ostomy Purpose: A salvage procedure aimed at creating a permanent alternative opening for urination, specifically to prevent recurrent blockage from stones or strictures that cannot be otherwise managed.

Incision Techniques

  • The creation of a wider urethral opening in more proximal locations is crucial for preventing future obstructions by providing a larger diameter for stones to pass or by bypassing previously narrowed urethral segments. Adequate opening size minimizes the risk of fibrotic narrowing post-operatively.

  • Urethrostomy is indicated in cases of permanent damage or strictures that cause acute obstruction, especially when other medical or less invasive surgical interventions have failed or are deemed unsuitable.

  • Types of urethrostomy in dogs include scrotal, pre-scrotal, anti-pubic, and perineal. Each type is chosen based on the location of the obstruction and carries unique surgical approaches, risks, and potential complications specific to the anatomical site.

Complications of Urethrostomy

General Overview

  • Common complications include hematuria (blood in urine), infection (urinary tract infection), strictures (narrowing of the urethral opening), and urine scald (dermatitis caused by chronic urine exposure).

  • Hemorrhage: A major concern postpartum, as there is substantial vascular tissue (corpus spongiosum) in the area. This leads to excessive blood loss during surgery and potentially for several days post-operatively, often requiring careful hemostasis.

  • Urinary Tract Infection: Increased risk following urethrostomy due to the removal of normal anatomical barriers (e.g., longer urethra, natural urethral sphincter mechanism) that protect against ascending bacterial infections, and potential urine contamination of the surgical site.

Specific Complications and Management

  • Strictures: Typically result from poor surgical technique, such as insufficient tissue mobilization leading to tension, imprecise mucosa-to-skin apposition, or excessive inflammation and fibrosis. Proper tissue mobilization, everted mucosa, and appropriate suture placement are essential for preventing stricture formation.

  • Subcutaneous Urine Leakage: Can be detected during bladder expression or observed as swelling around the surgical site. This complication confirms a dehiscence or inadequate seal of the suture line, requiring a re-evaluation of the quality of the sutures and tissue approximation and often surgical revision.

  • Perineal Hernia: Can occur if the dissection deviates too widely or deeply from the urethral tube's vicinity during perineal urethrostomy. This can weaken the supporting musculature of the pelvic diaphragm, allowing abdominal or pelvic contents to herniate into the perineal region.

Conclusion

  • Understanding the anatomy and associated risks is critical in managing urethral obstructions and implementing urethrostomy procedures, especially in light of the potential complications described. Proper surgical technique and post-operative care are paramount for successful outcomes and minimizing adverse effects.