11.14.2025 - SAM2 - part 1
Morning Lecture Overview
Objective: Final day of the course, focused on the comprehensive review of heavy and critical material covered throughout the curriculum.
Block cat overview: This session will expand on practical clinical knowledge related to feline urethral obstruction, bridging theoretical learning with real-world application.
Presentation of three case studies: These cases will serve to consolidate learning by applying diagnostic and therapeutic principles to complex scenarios.
Guidance on revision focus: Instructors will highlight key areas and concepts essential for effective course review and long-term retention.
Lecture Goals
Recognize clinical signs indicative of urethral obstruction: This includes both overt and subtle signs that owners or veterinary staff might observe, emphasizing the urgency of early detection.
Understand the implications of hyperkalemia and its treatment: Focus on its life-threatening cardiac effects and the detailed management strategies.
Knowledge of principles to relieve a blocked cat: Encompasses the procedural steps, necessary equipment, and critical considerations for safe and effective urethral catheterization.
Emphasize the significance of sepsis and trauma: Understanding how these secondary complications arise from urethral obstruction and their impact on patient prognosis.
Investigate underlying causes of urethral obstruction: This involves a systematic approach to diagnosis, crucial for preventing recurrence and implementing long-term management.
Clinical Signs of Urethral Obstruction in Cats
Common signs previously covered include:
Urea levels: Indicators of azotemia (e.g., elevated BUN and creatinine), reflecting impaired renal function due to post-renal obstruction.
Hematuria: Presence of blood in urine, ranging from gross (macroscopic) to microscopic, often due to irritation or trauma within the urinary tract.
Straining to urinate (stranguria/dysuria): Frequent attempts to urinate with little or no urine production, often accompanied by vocalization or hunched posture.
Some signs may be missed by owners (e.g., cats that toilet outdoors): This is especially true if owners are not observing their cat's urination habits diligently, delaying presentation until severe compromise.
Owners may misinterpret symptoms, thinking they are due to constipation: The straining associated with urethral obstruction can be mistaken for tenesmus related to fecal issues, leading to inappropriate at-home treatment or delayed veterinary care.
Consequences of missed signs: Can lead to the presentation of a collapsed cat without prior history, indicating severe decompensation.
Symptoms may include:
Vomiting due to pain: Can be a systemic response to severe pain, uremic toxins, or electrolyte imbalances.
Vocalizing: Cries or persistent meowing indicating severe discomfort or pain.
Lethargy after not eating for 40 hours: Anorexia and profound weakness are signs of systemic illness, metabolic derangements, and uremia.
Presentation may show significant metabolic abnormalities: This includes severe metabolic acidosis, hyperkalemia, acute kidney injury, and potentially hypocalcemia.
May collapse: Due to shock, cardiac arrhythmias from hyperkalemia, or severe dehydration and electrolyte imbalances.
Physical examination findings:
Identification of a large, tense, painful bladder (cystomegaly): A hallmark sign, often palpable as a hard, distended mass in the caudal abdomen.
Bladder may not be palpable if it has ruptured: A ruptured bladder leads to uroabdomen, where urine leaks into the abdominal cavity, alleviating bladder distension but causing severe peritonitis.
May exhibit altered mental status: Ranging from depression and obtundation to stupor, indicative of severe metabolic encephalopathy or shock.
Respiratory patterns may indicate acidosis (e.g., rapid, deep breathing — Kussmaul respirations): The body's compensatory mechanism to expel carbon dioxide and mitigate metabolic acidosis.
Physiological Effects of Urethral Obstruction
Bradycardia: Common in cats in shock, often showing a slow heart rate (e.g., <120 bpm), which is unusual for a cat in pain or stress, and frequently associated with severe hyperkalemia's effects on myocardial function.
Hypothermia: Indicates poor prognosis and should be assessed carefully, as it often reflects severe systemic shock, poor perfusion, and metabolic collapse.
Contrast between two clinical scenarios:
Reasonably healthy cat with painful blockage: May have been obstructed for less than 24 hours, presenting with pain, a distended bladder, but with relatively stable cardiovascular parameters and less severe metabolic derangements.
Severely compromised cat in shock: Typically obstructed for over 24-36 hours, presenting collapsed, hypothermic, bradycardic, with significant metabolic acidosis, severe hyperkalemia, and acute renal failure.
Initial Management of Blocked Cats
Intravenous fluid therapy is essential: Administered even if the cat can urinate temporarily, as it is crucial for addressing dehydration, correcting metabolic abnormalities, re-establishing renal perfusion, and preparing for anesthesia.
Purpose: To address severe metabolic abnormalities (e.g., acidosis, hyperkalemia) and prepare the patient for safe anesthesia and catheterization.
Analgesia with opioids: Methadone and fentanyl are preferred for pain relief due to their effective analgesic properties and minimal cardiovascular depressant effects, crucial for a compromised patient. This also helps relax the urethral sphincter.
Treatment of Hyperkalemia
Most concerning metabolic abnormality due to its profound and potentially fatal effect on cardiac function, often leading to life-threatening arrhythmias or asystole.
Cats typically present with metabolic acidosis: This condition exacerbates hyperkalemia, as hydrogen ions move into cells and potassium moves out to maintain electrical neutrality.
High potassium levels (e.g., >7 mmol/L): Can lead to serious cardiac issues, with values >9-10 mmol/L being critically life-threatening.
Initial measures in case of hyperkalemia include:
Intravenous fluids to dilute potassium and restore circulation: Crystalloid fluids (e.g., LRS or 0.9% NaCl) help dilute serum potassium and promote its urinary excretion by improving renal perfusion and glomerular filtration.
Lactate Ringer's solution preferred over normal saline to avoid worsening acidosis: Lactate in LRS is metabolized to bicarbonate in the liver, which helps to buffer existing metabolic acidosis and can slightly shift potassium back into cells.
Metabolic Status and Diagnostics
Minimum laboratory testing includes:
Urea, creatinine: To assess the severity of azotemia and acute kidney injury.
Phosphate: Often elevated in renal failure and can indicate chronicity or severity of the obstruction.
Potassium: Crucial for assessing hyperkalemia and guiding its treatment.
Ionized calcium: Important as hyperkalemia can have additive negative effects on cardiac conduction, and imbalances can occur with renal failure.
Acid-base status: To determine the degree of metabolic acidosis and monitor response to fluid therapy and other interventions.
EKG monitoring: To assess heart rhythm and electrical activity for effects from hyperkalemia and other metabolic derangements, providing immediate feedback on cardiac stability.
EKG Changes to Monitor in Cats with Hyperkalemia
Common EKG abnormalities, which progress with increasing potassium levels:
Wide or tall T waves: Reflect abnormal ventricular repolarization.
Absent P waves (indicating atrial standstill): Occurs as atrial depolarization is overridden by sustained high potassium levels, which makes the atrial myocardium inexcitable.
Prolonged PR intervals: Suggests delayed conduction through the atrioventricular (AV) node.
ST segment depression: Can be a non-specific finding but may be present.
Wide QRS complex: Indicates slowed ventricular depolarization, representing a severe and immediate threat to cardiac function.
Calcium gluconate used for stabilizing cardiac conduction: Administered intravenously, it directly antagonizes the cardiotoxic effects of hyperkalemia by increasing the threshold potential of myocardial cells, thereby protecting the heart. Ca2+Ca2+ does not, however, lower potassium levels directly; its effect is rapid but short-lived.
Additional Treatments to Lower Potassium
Glucose administration stimulates endogenous insulin release, which drives potassium intracellularly:
Administer as a diluted solution (e.g., 50% dextrose diluted to 5-10% in fluids) due to potential for irritation and phlebitis if given concentrated in peripheral veins.
Insulin can also be given exogenously (e.g., regular insulin at 0.1−0.2 U/kg0.1−0.2 U/kg IV), but requires concurrent glucose administration to prevent iatrogenic hypoglycemia, as insulin also drives glucose into cells.
Consideration of beta-agonists (e.g., albuterol): As adjunct therapy, these drugs (administered nebulized or systemically) promote potassium shift into cells by stimulating the Na+/K+-ATPase pump.
Sodium bicarbonate may also lower serum potassium: By inducing a metabolic alkalosis, it can cause potassium to shift from the extracellular to intracellular space. However, it poses risks such as hyponatremia, volume overload, and potential paradoxical central nervous system acidosis, and should be used cautiously and precisely.
Catheterization for Urethral Obstruction
After stabilizing the patient: Catheterization is essential for relieving blockage once the cat's hyperkalemia is managed, hydration is improved, and metabolic acidosis is corrected, ensuring the patient is hemodynamically stable enough for anesthesia.
Assess if cat is stable enough for anesthesia: This involves evaluating vital signs, EKG, blood pressure, and overall mentation. Monitor heart rate and EKG continuously throughout the procedure.
Ensure patient safety: This includes employing strict aseptic technique, careful selection of anesthetic agents that minimize cardiovascular depression, and continuous monitoring of vital parameters.
Reduce urethral trauma: Gentle technique, adequate lubrication, and avoidance of excessive force are paramount to prevent iatrogenic injury, stricture formation, or urethral rupture.
Ensure adequate anesthesia: Proper pain control and muscle relaxation are necessary to allow for successful, atraumatic catheter passage and to minimize patient stress.
Catheter Types and Insertion Techniques
Jackson Catheter: Typically made of polypropylene, these are preferred for initial unblocking due to their rigidity, which helps to navigate and dislodge urethral plugs or stones. They often have a stylet to aid in insertion and are less ideal for long-term indwelling use due to potential for irritation.
Urethral Catheter: Flexible silicone or red rubber catheters (e.g., tomcat catheters) are suitable for flushing the urethra and are generally less irritating, making them preferred for long-term (indwelling) placement after the initial obstruction is relieved.
Adjustments during catheterization include maintaining sterile conditions: This involves sterile gloves, drapes, and antiseptic preparation of the perineal area to prevent ascending urinary tract infections. Possible use of rectal examination can aid in catheter placement by allowing palpation of the urethra and gentle guidance of the catheter tip past the obstruction.
Ensure proper positioning of the cat: Sternal recumbency with the hindlimbs pulled cranially often facilitates easier catheterization by straightening the male cat's urethra.
Post-Catheterization Care
After initial placement, assess urine output: Monitor the volume of urine produced (often significant polyuria initially due to post-obstructive diuresis), its color (initially bloody, then clearing), and clarity.
Perform urinalysis: To identify the presence of crystals, inflammation, infection (via culture), and determine urine specific gravity.
Adjust catheter techniques based on the specific symptoms and presence of obstruction: This may include regular flushing of the catheter to maintain patency or adjusting the catheter type.
Monitoring of urine characteristics (e.g., color, clarity, debris presence) is critical: Observing for signs of persistent hematuria, pyuria, or sediment can guide further diagnostics and treatment.
Management of Aftercare and Complications
Leave the catheter in place for up to 36 hours post-procedure: This allows the urethral spasm to resolve, the inflamed urethral mucosa to heal, and ensures adequate initial post-obstructive diuresis without immediate risk of re-obstruction.
Maintain proper hygiene of collection systems to prevent infection: This includes using a closed collection system and regularly emptying the collection bag, along with cleaning the external catheter insertion site.
Monitor for signs of infection or reinfection post-obstruction therapy: This includes observing for fever, changes in urine characteristics, or signs of systemic illness, necessitating follow-up urinalysis and culture.
Recurrence Management and Considerations
High recurrence rate of urinary obstruction: This is a major challenge for owners and veterinarians, with idiopathic cystitis, urolithiasis, and urethral plugs being primary culprits.
Up to 50-60% of cats may experience recurrence: This often leads to significant owner frustration, financial burden, and, unfortunately, can contribute to euthanasia decisions.
Emphasize thorough investigation of underlying causes: This includes complete urinalysis, urine culture and sensitivity, urinary imaging (radiographs, ultrasound) to identify uroliths or other anatomical abnormalities, and evaluating for feline idiopathic cystitis (FIC) triggers.
Managing recurrent infections: Prompt diagnosis and appropriate antibiotic therapy based on culture and sensitivity results are critical.
Explore neoplasms as potential issues: While less common, especially in older cats, urinary tract tumors (e.g., transitional cell carcinoma) should be considered in cases of chronic or recurrent obstruction unresponsive to standard therapy.
Conclusion and Final Considerations
Recognition of hyperkalemia as a priority: Above immediate obstruction treatment is critical, as cardiac effects of hyperkalemia are often the most immediate life-threatening concern.
Avoid aggressive measures leading to urethral trauma: Emphasizes the importance of gentle, atraumatic catheterization techniques to prevent long-term complications such as strictures or bladder rupture. Ensure staff are aware of the urgency of managing such cases as well as the delicate nature of the procedure.
Participants encouraged to focus review on critical concepts for patient management: This extends beyond immediate issues to include comprehensive follow-up care, strategies for prevention of recurrences in affected cats (e.g., dietary management, environmental enrichment for FIC), and owner education.