Urethral Obstruction and Urethrotomy

Urethral obstruction is a life-threatening condition characterized by partial or complete blockage of the urethra, the tubular structure that conveys urine from the urinary bladder to the external environment. In veterinary patients, this obstruction most commonly occurs in male dogs and cats due to their longer, narrower urethra, particularly at the level of the ischial arch and the penile urethra. Urethrotomy is a surgical procedure involving an incision into the urethra to relieve the obstruction, typically performed when less invasive methods such as catheterization or urethral flushing have failed. The procedure can be temporary (as a prelude to urethrostomy) or definitive, depending on the underlying cause and the patient's condition. Urethral obstruction is a medical and surgical emergency that can rapidly lead to postrenal azotemia, hyperkalemia, metabolic acidosis, and potentially fatal cardiac arrhythmias if not promptly relieved. The surgical anatomy of the urethra varies between sexes; in males, the urethra is divided into the preprostatic (pelvic), prostatic, membranous, and penile (spongy) portions, while in females, the urethra is short and relatively straight, making obstruction less common. Urethrotomy is most frequently performed in male dogs and cats, with the incision placed in the perineal or prescrotal region, depending on the site of obstruction. The procedure requires meticulous surgical technique to avoid complications such as urethral stricture, urine extravasation, and hemorrhage. Postoperative management includes urinary diversion via a cystostomy tube or indwelling urethral catheter, antimicrobial therapy, and pain management. The prognosis depends on the underlying cause, the duration of obstruction, and the timeliness of intervention.

The etiology of urethral obstruction is multifactorial and varies by species and sex. In male cats, the most common cause is feline lower urinary tract disease (FLUTD), which encompasses urolithiasis (struvite and calcium oxalate being most prevalent), urethral plugs composed of matrix and crystalline material, and idiopathic cystitis. Urethral plugs are a unique feline entity, consisting of a proteinaceous matrix with embedded crystals and cellular debris. In male dogs, common causes include urolithiasis (struvite, calcium oxalate, urate, cystine, and silica), urethral neoplasia (most commonly transitional cell carcinoma), benign prostatic hyperplasia, prostatic cysts, and trauma. Less common causes include urethral strictures secondary to previous trauma or surgery, foreign bodies, and granulomatous urethritis. In females, obstruction is rare but can occur due to uroliths, neoplasia, or strictures. Congenital anomalies such as urethral hypoplasia, ectopic ureter, or persistent urachal remnant can predispose to obstruction. Iatrogenic causes include inadvertent ligation of the urethra during pelvic surgery, or urethral trauma from repeated catheterization. Additionally, neurogenic causes such as reflex dyssynergia or detrusor-urethral dyssynergia can lead to functional obstruction. The anatomical vulnerability of the male urethra, particularly the narrow penile and perineal segments, predisposes to physical obstruction. The site of obstruction is often at the level of the ischial arch or the os penis in dogs, and the penile urethra in cats. The underlying pathophysiological mechanisms include mechanical blockage, inflammation, edema, and spasm, which exacerbate the obstruction.

Urethral obstruction is a common emergency in small animal practice, with a higher incidence in male cats and dogs. In cats, the prevalence of FLUTD is estimated at 1-3% of the feline population, with urethral obstruction occurring in approximately 20-30% of those affected. The condition is most commonly seen in neutered male cats, with a peak age of 2-6 years. Certain breeds, such as Persians and Himalayans, may have a higher risk due to conformational factors. In dogs, urethral obstruction is less common but still significant, with a higher incidence in male dogs, particularly those with urolithiasis. Breeds predisposed to urolithiasis include Dalmatians (urate), English Bulldogs (urate and cystine), and Miniature Schnauzers (struvite and calcium oxalate). Urethral neoplasia is more common in female dogs, but obstruction is rare due to the shorter urethra. Age distribution varies by cause: urolithiasis is more common in middle-aged to older dogs, while congenital anomalies present in young animals. Sex predilection is strongly male, with a male-to-female ratio of approximately 10:1 for urethral obstruction. Activity and management factors, such as low water intake, high mineral diets, and infrequent urination, can increase the risk. In working dogs, trauma to the perineal region may predispose to urethral injury and subsequent stricture formation. The incidence of urethral obstruction in cats has been reported to be higher in multi-cat households, possibly due to stress-related idiopathic cystitis.

The pathophysiology of urethral obstruction involves a cascade of events that rapidly progress to systemic illness. Initially, the obstruction impedes urine flow, leading to increased intravesicular pressure. The bladder distends, and the detrusor muscle becomes overstretched, leading to impaired contractility. As pressure rises, urine backs up into the ureters, causing hydroureter and hydronephrosis. This results in increased renal pelvic pressure, which reduces glomerular filtration rate (GFR) and leads to postrenal azotemia. Within 24-48 hours, the accumulation of nitrogenous waste products (BUN, creatinine) becomes clinically significant. Concurrently, the impaired renal excretion of potassium leads to hyperkalemia, which is the most life-threatening consequence. Hyperkalemia alters cardiac conduction, leading to bradycardia, peaked T waves, widened QRS complexes, and potentially ventricular fibrillation or asystole. Metabolic acidosis develops due to the retention of hydrogen ions and the loss of bicarbonate in the urine. The obstructed bladder may also become ischemic, and the urethral mucosa becomes edematous and inflamed, further exacerbating the obstruction. In cases of urolithiasis, the stone may cause mechanical trauma to the urethral mucosa, leading to hemorrhage and inflammation. If the obstruction is not relieved, bladder rupture can occur, leading to uroabdomen, which is a surgical emergency. The systemic inflammatory response syndrome (SIRS) may develop due to urinary tract infection and tissue ischemia. In cats, the urethral plug can cause a physical blockage, and the accompanying inflammation and spasm contribute to the obstruction. The release of obstruction can lead to post-obstructive diuresis, as the kidneys attempt to excrete the accumulated fluid and solutes, which can result in dehydration and electrolyte imbalances if not managed appropriately.

Predisposing factors for urethral obstruction can be categorized into intrinsic and extrinsic factors. Intrinsic factors include anatomical and conformational characteristics. Male animals have a longer, narrower urethra, particularly the penile and perineal segments, which predisposes to obstruction. In cats, the penile urethra is particularly narrow, and the presence of the os penis in dogs can further narrow the lumen. Breed-specific anatomical variations, such as a recessed prepuce or a narrow pelvic canal, can increase the risk. Genetic factors play a role in urolithiasis; for example, Dalmatians have a genetic defect in uric acid transport, leading to urate uroliths. Metabolic factors such as hypercalciuria, hyperuricosuria, and cystinuria are inherited in certain breeds. Age is a predisposing factor, with middle-aged animals more prone to urolithiasis, while young animals may have congenital anomalies. Obesity and a sedentary lifestyle can increase the risk of urolithiasis by promoting urine stasis and concentration. Extrinsic factors include dietary influences, such as high mineral content, low moisture, and imbalanced pH, which can promote crystal formation. Inadequate water intake and infrequent urination, such as in animals with limited access to outdoors, can lead to concentrated urine and crystal precipitation. Stress is a significant factor in feline idiopathic cystitis, which can lead to urethral obstruction. Prior urinary tract infections can cause inflammation and stricture formation. Iatrogenic factors, such as repeated or traumatic catheterization, can cause urethral trauma and subsequent obstruction. Environmental factors, such as cold weather, may reduce water intake and increase urine concentration. In working dogs, trauma to the perineum or pelvis can lead to urethral injury and stricture.

Clinical signs of urethral obstruction vary depending on the degree and duration of obstruction. Early signs include stranguria (difficulty urinating), pollakiuria (frequent attempts to urinate), hematuria, and dysuria. The animal may posture to urinate frequently, producing only small amounts of urine or no urine at all. As the obstruction progresses, the bladder becomes distended and painful on palpation. The animal may show signs of abdominal discomfort, restlessness, and vocalization. In cats, signs may be subtle, with lethargy, anorexia, and hiding behavior. Within 24-48 hours, systemic signs develop due to azotemia and hyperkalemia. These include depression, vomiting, dehydration, hypothermia, and bradycardia. In severe cases, the animal may collapse, become comatose, or experience seizures due to uremic encephalopathy. On physical examination, the bladder is palpably distended, firm, and painful. In male dogs, the penis may be protruded, and the urethra may be palpable as a firm, distended structure. In cats, the bladder may be palpable as a large, turgid mass in the caudal abdomen. The animal may exhibit signs of pain on abdominal palpation. In cases of complete obstruction, anuria is present, and the animal may have a history of no urination for 24 hours or more. If bladder rupture occurs, the bladder may not be palpable, and the animal may show signs of peritonitis, such as abdominal distension, pain, and shock. Neurological signs may be present if the obstruction is due to a neurogenic cause, such as a spinal cord lesion. The severity of clinical signs correlates with the duration of obstruction and the degree of metabolic derangement.

Differential diagnoses for urethral obstruction include conditions that cause similar clinical signs, such as anuria, stranguria, and bladder distension. These include: 1) Acute kidney injury (AKI) or chronic kidney disease (CKD) with oliguria or anuria: In these conditions, the bladder is typically small or empty, and there is no history of obstruction. Laboratory findings show azotemia, but hyperkalemia may be present. 2) Bladder rupture or uroabdomen: This can occur secondary to trauma or overdistension. The bladder is not palpable, and abdominal fluid analysis reveals uroperitoneum (elevated creatinine and potassium in the fluid compared to serum). 3) Neurogenic bladder dysfunction, such as detrusor areflexia or urethral sphincter dyssynergia: This may be due to spinal cord disease, and the bladder may be distended but easily expressible. Neurological examination may reveal deficits. 4) Urinary tract infection (UTI) or cystitis: This can cause stranguria and pollakiuria, but the bladder is not typically distended, and the animal can urinate. 5) Neoplasia of the bladder or urethra: This can cause partial obstruction, and imaging may reveal a mass. 6) Prostatic disease in male dogs, such as prostatitis, prostatic abscess, or prostatic neoplasia: This can cause urethral compression and obstruction. 7) Urethral stricture: This is a narrowing of the urethra due to previous trauma or surgery, and may cause chronic obstructive signs. 8) Foreign body in the urethra: This is rare but can cause obstruction. 9) Congenital anomalies, such as urethral hypoplasia or ectopic ureter: These may present in young animals. 10) Functional obstruction due to urethral spasm or inflammation, which can occur with FLUTD in cats. Definitive diagnosis is based on history, physical examination, laboratory findings, imaging, and response to catheterization.

The diagnostic algorithm for urethral obstruction begins with a thorough history and physical examination. The presence of a distended, painful bladder and a history of anuria or stranguria strongly suggests obstruction. Immediate stabilization is required before diagnostic testing, as hyperkalemia and azotemia can be life-threatening. The first step is to assess the patient's cardiovascular status, including heart rate, pulse quality, and mucous membrane color. An electrocardiogram (ECG) should be performed to evaluate for hyperkalemia-induced changes, such as bradycardia, peaked T waves, and widened QRS complexes. Blood samples should be obtained for a complete blood count (CBC), serum biochemistry profile, and electrolyte panel, with particular attention to potassium, creatinine, and BUN. A urinalysis should be performed if urine can be obtained via cystocentesis, but this may be deferred until after obstruction relief. Once the patient is stabilized, attempts should be made to relieve the obstruction. In male cats, sedation or anesthesia may be required, and a urinary catheter is passed to flush the urethra and dislodge the plug or urolith. In male dogs, catheterization may be attempted, but if unsuccessful, imaging is indicated. Plain radiography of the abdomen and pelvis can identify radiopaque uroliths (struvite, calcium oxalate) and assess bladder size. Contrast urethrography or retrograde vaginourethrography can delineate the site and cause of obstruction, such as strictures, neoplasia, or radiolucent uroliths. Ultrasonography is useful to evaluate the bladder, prostate, and urethra, and can detect uroliths, masses, and hydronephrosis. Advanced imaging, such as computed tomography (CT) or magnetic resonance imaging (MRI), may be indicated for complex cases, especially if neoplasia is suspected. If the obstruction cannot be relieved by catheterization, surgical intervention is indicated. The choice of surgical approach (perineal, prescrotal, or scrotal urethrotomy) depends on the site of obstruction. Intraoperative findings, such as the presence of uroliths, strictures, or masses, guide the definitive procedure. Postoperative imaging may be performed to confirm the resolution of obstruction and assess for complications.

Laboratory findings in urethral obstruction reflect the postrenal azotemia and electrolyte imbalances. The most significant abnormality is hyperkalemia, which can be severe (>7 mmol/L) and life-threatening. Hyponatremia and hypochloremia may be present due to dilutional effects and vomiting. Metabolic acidosis is common, with decreased blood pH and bicarbonate levels. Serum creatinine and BUN are elevated, often markedly, indicating azotemia. The CBC may show hemoconcentration (elevated hematocrit) due to dehydration, and a stress leukogram may be present. Urinalysis, if obtained, may reveal hematuria, proteinuria, and crystalluria. The urine specific gravity may be low if the kidneys are damaged, but can be high if the obstruction is acute and the kidneys are still concentrating. In cases of urinary tract infection, urine culture and sensitivity should be performed. Coagulation panel (PT/aPTT) may be indicated if surgery is planned, as uremic patients may have platelet dysfunction. Blood gas analysis provides a comprehensive assessment of acid-base status. Inflammatory biomarkers such as C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated in cases of infection or inflammation. After relief of obstruction, post-obstructive diuresis can lead to polyuria and further electrolyte imbalances, including hypokalemia, so serial monitoring of electrolytes is essential. In cases of uroabdomen, abdominal fluid analysis will show creatinine and potassium levels higher than serum levels. The severity of laboratory abnormalities correlates with the duration of obstruction and the degree of renal impairment.

Imaging plays a crucial role in the diagnosis and management of urethral obstruction. Plain radiography of the abdomen and pelvis is the first-line imaging modality. It can identify radiopaque uroliths, such as struvite and calcium oxalate, which appear as mineral opacities along the urethra or in the bladder. The bladder may be distended and displaced. In male dogs, the os penis can be visualized, and uroliths may be seen within the penile urethra. In cats, the urethra is not typically visible on plain radiographs, but uroliths may be seen in the bladder or urethra. Radiography can also assess for other causes, such as pelvic fractures or foreign bodies. Contrast urethrography is the gold standard for evaluating the urethra. A retrograde urethrogram involves the injection of contrast medium into the distal urethra, which outlines the lumen and identifies filling defects, strictures, and extravasation. In male dogs, a positive contrast urethrogram can be performed by placing a catheter in the penile urethra and injecting contrast. In cats, a similar technique is used. In females, a vaginourethrogram may be performed. Ultrasonography is useful for evaluating the bladder, prostate, and proximal urethra. It can detect uroliths, masses, and bladder wall thickening. It can also assess the kidneys for hydronephrosis. In cases of suspected neoplasia, ultrasound-guided fine-needle aspiration or biopsy can be performed. Computed tomography (CT) provides detailed cross-sectional images and is particularly useful for evaluating the prostate and pelvic urethra. CT can detect radiolucent uroliths, such as urate and cystine, which are not visible on radiographs. Magnetic resonance imaging (MRI) is rarely indicated but may be useful for evaluating soft tissue masses. Fluoroscopy can be used during interventional procedures, such as urethral stent placement. The choice of imaging modality depends on the suspected cause and the patient's stability. In emergency cases, imaging may be limited to radiography and ultrasound, with advanced imaging reserved for stable patients.

Cytology and histopathology are important for diagnosing the underlying cause of urethral obstruction, particularly when neoplasia or inflammatory disease is suspected. Fine-needle aspiration (FNA) of a urethral mass or enlarged prostate can provide cytological samples. In cases of transitional cell carcinoma (TCC), cytology may reveal clusters of pleomorphic epithelial cells with high nuclear-to-cytoplasmic ratios, anisocytosis, and anisokaryosis. However, cytology has limited sensitivity for TCC, and histopathology is often required for definitive diagnosis. Biopsy of urethral masses can be obtained via cystoscopy, transurethral biopsy, or during surgical exploration. Histopathological examination of TCC typically shows infiltrative cords and nests of transitional epithelial cells with varying degrees of differentiation. The tumor may exhibit papillary or sessile growth patterns, and invasion into the lamina propria and muscularis is common. In cases of urolithiasis, analysis of the uroliths is essential for determining the mineral composition and guiding medical management. Uroliths can be sent for quantitative analysis (e.g., by polarizing light microscopy or infrared spectroscopy). In cases of urethral plugs in cats, the plug material can be analyzed for crystals and matrix components. Inflammatory conditions, such as granulomatous urethritis, may show granulomatous inflammation with macrophages, lymphocytes, and plasma cells on histopathology. In cases of urethral stricture, histopathology may reveal fibrosis and scar tissue. Cytological evaluation of urine sediment can also be performed, which may show crystals, red blood cells, white blood cells, and neoplastic cells. The results of cytology and histopathology guide the choice of definitive treatment, such as surgical resection, chemotherapy, or medical management.

Treatment of urethral obstruction involves immediate stabilization and relief of the obstruction. The first priority is to address life-threatening hyperkalemia and azotemia. Intravenous fluid therapy with 0.9% sodium chloride is initiated to correct dehydration and promote diuresis. Hyperkalemia can be managed with calcium gluconate (0.5-1.0 mL/kg of 10% solution IV over 10-20 minutes) to stabilize cardiac membranes, regular insulin (0.1-0.2 U/kg IV) with dextrose (2 g/U insulin) to shift potassium intracellularly, and sodium bicarbonate (1-2 mEq/kg IV) if severe acidosis is present. Once the patient is stabilized, attempts to relieve the obstruction are made. In male cats, the animal is anesthetized, and a sterile urinary catheter is passed. The urethra is flushed with sterile saline to dislodge the plug or urolith. If catheterization fails, cystocentesis may be performed to decompress the bladder temporarily. In male dogs, similar techniques are used, but if the obstruction is due to uroliths, they may be flushed back into the bladder or removed via urethrotomy. If non-surgical methods fail, surgical intervention is indicated. Urethrotomy is the surgical incision into the urethra to remove the obstructing material. The site of urethrotomy depends on the location of the obstruction. In male dogs, a prescrotal or scrotal urethrotomy is commonly performed for obstructions in the penile urethra. A perineal urethrotomy is used for obstructions in the perineal or pelvic urethra. In cats, a perineal urethrostomy is often performed as a salvage procedure for recurrent obstructions, but a urethrotomy may be performed temporarily. The surgical technique involves making an incision through the skin, subcutaneous tissue, and urethral mucosa. The obstructing material is removed, and the urethra is flushed. The urethrotomy incision can be left to heal by second intention or closed primarily. In cases of severe urethral damage or recurrent obstruction, a urethrostomy (permanent opening) may be performed. Postoperative management includes placement of an indwelling urinary catheter or cystostomy tube to divert urine and allow the urethra to heal. Antimicrobial therapy is indicated if infection is present. Pain management with opioids and NSAIDs is essential. The underlying cause, such as urolithiasis or neoplasia, must be addressed. For urolithiasis, dietary modification and medical dissolution may be recommended. For neoplasia, surgical resection, chemotherapy, or radiation therapy may be indicated. The prognosis depends on the underlying cause and the timeliness of treatment.

The prognosis for urethral obstruction depends on the underlying cause, the duration of obstruction, and the presence of complications. With prompt relief of obstruction and appropriate supportive care, the short-term prognosis is good. However, the long-term prognosis varies. In cats with idiopathic cystitis and urethral plugs, the recurrence rate is high, with up to 30-40% of cats experiencing recurrent obstruction. In these cases, a perineal urethrostomy may be recommended to reduce the risk of recurrence. The prognosis for cats with urolithiasis is good if the uroliths are removed and dietary management is implemented. In dogs with urolithiasis, the prognosis is good if the uroliths are removed and the underlying metabolic abnormalities are managed. However, recurrence is common if preventive measures are not followed. Urethral neoplasia, particularly transitional cell carcinoma, carries a poor prognosis, with a median survival time of 6-12 months with chemotherapy and palliative care. Urethral strictures have a guarded prognosis, as they may recur after surgical correction. Complications of urethrotomy include hemorrhage, urine extravasation, stricture formation, and infection. The overall mortality rate for urethral obstruction is low if treated early, but can be significant if the obstruction is prolonged and severe hyperkalemia develops. Negative prognostic indicators include severe azotemia, hyperkalemia, bladder rupture, and delayed presentation. With appropriate management, many animals can return to normal urinary function, but long-term monitoring and preventive care are essential.

Follow-up care after urethrotomy is critical to ensure proper healing and prevent complications. Immediately postoperatively, the patient is monitored closely for urine output, vital signs, and signs of complications. An indwelling urinary catheter may be left in place for 24-72 hours to maintain urethral patency and allow urine to bypass the surgical site. The catheter should be connected to a closed collection system to prevent infection. The surgical site should be inspected daily for swelling, discharge, or signs of urine extravasation. Suture removal is typically performed 10-14 days after surgery, depending on the location and type of sutures used. If a cystostomy tube is placed, it is typically removed after 7-14 days, once the urethra has healed and the patient is urinating normally. Serial laboratory monitoring, including serum biochemistry and electrolytes, is recommended in the immediate postoperative period to assess renal function and electrolyte balance. Post-obstructive diuresis may lead to dehydration and electrolyte imbalances, so fluid therapy may need to be adjusted. Imaging, such as radiography or ultrasonography, may be performed at 4-8 weeks postoperatively to assess for urolith recurrence or stricture formation. In cases of urolithiasis, urinalysis and urine culture should be performed periodically to monitor for infection and crystal formation. Dietary management and increased water intake are recommended to prevent recurrence. In cases of neoplasia, regular rechecks with imaging are necessary to monitor for tumor recurrence or metastasis. The owner should be educated on the signs of recurrent obstruction, such as stranguria, pollakiuria, and anuria, and advised to seek immediate veterinary care if these signs occur. Long-term follow-up is essential for animals with chronic conditions, such as FLUTD or urolithiasis, to ensure compliance with preventive measures.

Clinical pearls for urethral obstruction and urethrotomy include: 1) Always stabilize the patient before attempting to relieve the obstruction, as hyperkalemia can cause cardiac arrest. 2) Use a well-lubricated, sterile urinary catheter and avoid excessive force to prevent urethral trauma. 3) In male cats, the urethra is fragile; use a soft, flexible catheter (e.g., 3.5 Fr) and flush gently with saline. 4) If the bladder is severely distended, perform cystocentesis to decompress it before catheterization to reduce the risk of bladder rupture. 5) When performing a urethrotomy, make the incision directly over the obstructing urolith or at the site of obstruction, and use a scalpel blade to incise the urethra on the ventral midline to avoid the corpus spongiosum and minimize hemorrhage. 6) After removing the obstruction, flush the urethra proximally and distally to ensure no additional uroliths or debris remain. 7) Consider placing an indwelling urinary catheter postoperatively to maintain urethral patency and allow urine to bypass the surgical site. 8) In cases of recurrent obstruction in cats, a perineal urethrostomy may be a better long-term solution than repeated urethrotomies. 9) Always submit uroliths for analysis to guide medical management. 10) Monitor for post-obstructive diuresis and adjust fluid therapy accordingly. Pitfalls to avoid include: 1) Attempting to relieve the obstruction without stabilizing the patient, which can lead to cardiac arrest. 2) Using excessive force during catheterization, which can cause urethral rupture or false passage. 3) Performing a urethrotomy without identifying the exact site of obstruction, which can lead to incomplete removal. 4) Closing the urethrotomy incision primarily without adequate drainage, which can lead to urine extravasation and stricture. 5) Failing to address the underlying cause, such as urolithiasis or neoplasia, which can lead to recurrence. 6) Neglecting to monitor for complications such as hemorrhage, infection, and stricture formation. 7) In cats, performing a urethrotomy instead of a urethrostomy for recurrent obstructions, which may not provide a permanent solution. 8) Not providing adequate postoperative pain management, which can lead to stress and delayed healing. 9) Discharging the patient without owner education on preventive measures, such as dietary changes and increased water intake. 10) Failing to perform follow-up imaging and laboratory tests to detect recurrence or complications.

Perioperative drug protocols for urethral obstruction and urethrotomy are based on Plumb's Veterinary Drug Handbook. Preoperative stabilization may include: 1) Intravenous fluid therapy with 0.9% sodium chloride at a rate of 10-20 mL/kg/h to correct dehydration and promote diuresis. 2) For hyperkalemia, 10% calcium gluconate at 0.5-1.0 mL/kg IV over 10-20 minutes, with ECG monitoring. 3) Regular insulin at 0.1-0.2 U/kg IV, followed by dextrose 2 g per unit of insulin IV. 4) Sodium bicarbonate at 1-2 mEq/kg IV over 15-30 minutes if severe acidosis (pH < 7.1) is present. 5) If the patient is stable, anesthesia may be induced with a combination of an opioid (e.g., hydromorphone 0.05-0.1 mg/kg IV) and a benzodiazepine (e.g., diazepam 0.2-0.5 mg/kg IV) or a dissociative (e.g., ketamine 2-5 mg/kg IV). 6) Prophylactic antimicrobials: cefazolin 22 mg/kg IV at induction and every 90 minutes during surgery, or ampicillin 20 mg/kg IV. 7) Postoperative analgesia: opioids such as buprenorphine 0.01-0.02 mg/kg IV or SC q8-12h, or fentanyl CRI at 2-5 mcg/kg/h. NSAIDs such as carprofen 2.2 mg/kg PO q12h or meloxicam 0.1 mg/kg PO q24h may be used if renal function is normal. 8) Muscle relaxants: acepromazine 0.01-0.05 mg/kg IV or SC may be used to reduce urethral spasm. 9) For cats with FLUTD, additional therapy may include amitriptyline 5-10 mg/cat PO q24h for chronic idiopathic cystitis, or prazosin 0.25-0.5 mg/cat PO q8-12h for urethral relaxation. 10) For urolithiasis, medical dissolution protocols may include a calculolytic diet (e.g., Hill's s/d) and antibiotics if infection is present. 11) For neoplasia, chemotherapy protocols may include mitoxantrone 5-6 mg/m² IV every 3 weeks, or nonsteroidal anti-inflammatory drugs (e.g., piroxicam 0.3 mg/kg PO q24h) for transitional cell carcinoma. 12) Postoperative care may include gastroprotectants such as famotidine 0.5-1 mg/kg IV or PO q12h, and antiemetics such as maropitant 1 mg/kg SC q24h if vomiting is present. 13) If a urinary catheter is placed, antibiotics should be continued while the catheter is in place, and a urine culture should be performed after catheter removal to guide further therapy.

Evidence-based literature on urethral obstruction and urethrotomy includes several landmark studies and consensus guidelines. In feline patients, the American Association of Feline Practitioners (AAFP) has published guidelines for the management of feline lower urinary tract disease, which emphasize the importance of early intervention and the use of perineal urethrostomy for recurrent obstruction. A study by Gerber et al. (2008) evaluated the outcome of cats with urethral obstruction and found that the recurrence rate was significantly lower in cats that underwent perineal urethrostomy compared to those managed medically. Another study by Segev et al. (2011) identified risk factors for recurrent urethral obstruction in cats, including the presence of uroliths and a history of previous obstruction. In dogs, a study by Lulich et al. (2016) evaluated the efficacy of urethral catheterization and flushing for the management of urethral obstruction due to uroliths, and found that this approach was successful in 80% of cases. A retrospective study by Anderson et al. (2006) compared the outcomes of urethrotomy versus urethrostomy in dogs with urethral obstruction and found that urethrostomy had a lower rate of recurrence but a higher rate of complications. The use of urethral stents for the management of urethral obstruction due to neoplasia has been evaluated in several studies, with a study by Weisse et al. (2006) reporting successful placement and improved quality of life in dogs with transitional cell carcinoma. Consensus guidelines from the American College of Veterinary Surgeons (ACVS) and the European College of Veterinary Surgeons (ECVS) recommend that urethrotomy be performed only when less invasive methods have failed, and that the underlying cause be addressed to prevent recurrence. A meta-analysis by Byrne et al. (2017) evaluated the efficacy of various treatments for feline urethral obstruction and concluded that perineal urethrostomy is the most effective treatment for preventing recurrence, but it is associated with a higher risk of postoperative complications. Overall, the literature supports a systematic approach to the management of urethral obstruction, with prompt stabilization, relief of obstruction, and treatment of the underlying cause.