When the Unblocking Gets Tough

Sarah Tauber, DVM, discusses the problems you may run into while unblocking a blocked male feline, and different troubleshooting techniques.

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Feline urethral obstruction is a common complication of feline lower urinary tract disease.  Approximately 12% of cats have metabolic derangements, which along with severe dehydration can cause patients to be critical.  Initial stabilization, adequate pain management, and a timely unblocking procedure can make feline urethral obstruction a treatable emergency with a high rate of survival.

Most of us veterinary professionals have had the cat with a urethral obstruction that didn’t seem to go as smoothly as we would have liked. I’d try all the tricks I have up my sleeve, get stuck, and call the surgeon in.  The surgeon would then proceed to unblock the cat (or dog) with ease and leave me feeling like I should have been able to complete the procedure without pulling the surgeon out of bed.  I have learned a few simple techniques from experiences, colleagues (and the surgeons) to try prior to calling the surgeon.  This article is not an inclusive article including diagnosis to discharge, rather focuses on the unblocking procedure itself.

Pain Control

One of the best preemptive management techniques is adequate pain control on presentation.  Improving pain control will provide comfort to the patient, minimize movement, decrease spasms of the urethra and decrease the risk of possible complications such as urethral inflammation and urethral tears.  Start with an opioid, oxymorphone for cats, hydromorphone for dogs are excellent choices, or morphine, fentanyl (bolus then CRI), or buprenorphine.  Adding on a benzodiazepine (midazolam) will help provide added muscle relaxation and aide with decreased resistance and spasm control during the procedure.  Other muscle relaxants such as diazepam, acepromazine, and dexmedetomidine may be used; however, may cause excessive sedation and hypotension pre-procedure. Acepromazine may not have an effect on the post-prostatic or penile urethra in anesthetized cats.

A sacrococcygeal block is an easy addition to multimodal pain control. This block can be used for additional pain management under anesthesia but can also be used for sick blocked cats to avoid anesthesia depending on the stability of the patient. The sacrococcygeal block provides anesthesia to the perineum, penis, colon and tail, and retains motor function to the pelvis by blocking the pudendal, pelvic, and caudal nerves in the cat.  The sacrococcygeal block is a great option in cats, however, a full epidural may be required for unblocking in a dog due to differences in the cessation of the spinal cord.

Finally, local infusion of lidocaine into the urethra may also provide additional local anesthesia during urinary catheter placement.


This is the first technique to use to attempt to relieve a possible obstruction in the urethra.  The urinary catheter should be placed into the urethra until resistance is met; then using a 12-20ml syringe filled with sterile saline, steady pulsing pressure of saline should be provided until the catheter can be introduced further into the urethra.  If dexterity is your strength, you may have additional control by performing the hydropulsion yourself.  Alternatively having an assistant perform the hydropulsion can give you an extra hand to pinch the urethral orifice around the urinary catheter to help provide added pressure into the urethra.

Alternative Urinary Catheter Types

Typically at DoveLewis, unblocking starts with a 3.5 french slippery sam (polytetrafluoroethylene) urinary catheter, providing enough rigidity, but cause less trauma to the urethra.  This catheter can also be left indwelling, and therefore may decrease urethral trauma with only one passage of a urinary catheter if able. If you are unable to relieve the obstruction with the use of hydropulsion, or addition of lidocaine into the urethra, different catheter types may be attempted.  A tomcat catheter (polypropylene) will add additional rigidity; however increase the risk for urethral irritation and urethral rupture.  A tomcat catheter should also not be left indwelling as the catheter has been shown to be more reactive to the urethra than alternative catheter types.  Red rubber catheters (polyvinyl) are not a great choice for the initial unblocking with the closed end and side holes, however are an option for indwelling catheter as it causes less urethral irritation, and softens when at body temperature.

A 3 french urinary catheter may be attempted, however may not be a good option to keep indwelling as it may increase chances of clogging the catheter and the patient urinating around the catheter.  A larger 5 french urinary catheter may be of benefit to decrease complications in catheter kinking or clogging, but the larger urinary catheter may cause increased trauma to the urethra and holds an increased risk in reobstruction in the first 24 hours post urinary catheter removal.  Lastly, a guide wire from a central line has occasionally been used due to the small size but retention of rigidity;- if the wire can be successfully placed into the urinary bladder, a slippery sam urinary catheter can be placed over the wire to guide it into the bladder lumen.  Risk of urethral tear or bladder tear/rupture may be slightly increased with this modality.

Changing Positioning

My preference is to place cats in dorsal recumbency with their legs pulled cranially.  However, should the unblocking prove difficult, changing the position may help - dorsal recumbency with the legs caudally, each lateral recumbancy, or even in ventral recumbency with legs hanging off of the table. In dogs, it may also help to elevate the pelvis with a towel and allow the legs to hang off of the table.


In cats, this may not be part of the initial physical examination.   A physical stone may be able to be palpated, and even pushed back into the urinary bladder. During hydropulsion, an assistant may place pressure on the urethra (via ventral pressure on the rectal wall) while infusing saline into the urethra, then quickly lifting pressure to also help increase pressure on a urethral plug.


A cystocentesis on an obstructed cat is not typically performed due to the high risk of urinary bladder trauma and possible rupture.  However, there are a few benefits of the procedure and therefore should be considered with difficult unblocking procedures. Performing the cystocentesis may help aide in decreasing the back pressure on a stone or crystalline plug making it easier to push into the urinary bladder.  Decompressing the urinary bladder will also help decrease the increased pressure on the kidneys, improving glomerular filtration.  Studies have shown that the actual risk of bladder rupture or laceration is low, and possible leaking through the centesis site causing a uroabdomen may not be of clinical consequence.  However, the risk of the procedure should be avoided if a timely unblocking can be performed, or if other techniques are able to accomplish a successful placement of the urinary catheter.


Typically with blocked cats, a radiograph is performed post unblocking to ensure adequate positioning of the urinary catheter in the bladder lumen, to determine if there are any uroliths, and finally ensure integrity of the urinary bladder and/or possible presence of peritoneal effusion.  However, if the unblocking proves difficult, performing a radiograph may help determine the cause of the difficulty such as multiple stones in the urethra, a possible mass, foreign body, etc.

Contrast Study

A positive contrast urethrogram can be of great benefit in looking for intraluminal obstruction- nonradiopaque stones, mass, foreign body, and can also diagnose a urethral tear or bladder rupture.  If a urinary catheter is unable to be passed, or if passage of the urinary catheter is not smooth into the urinary bladder or feels abnormal, a contrast study should be considered.  Omnipaque (Iohexol) is a contrast agent used at DoveLewis for lower urinary tract studies.  Omnipaque has a lower osmolality than other contrast agents, causing decreased toxicity and less irritation if the contrast leaks into the peritoneum.  To evaluate a urethral rupture, only 1-2 ml of contrast may be needed.  However if the contrast is to evaluate for urinary bladder rupture, increased contrast may be required to distend the urinary bladder. Dilute the contrast 1:2 with sterile saline; a total volume of 10-30ml/cat may be used.

Call in the Surgeon!

If the above treatment modalities do not achieve successful urinary catheter placement, it’s time to either refer, or call in the surgeon.  If a urethral tear is large, or if a urinary catheter cannot be successfully placed into the bladder, if the urinary bladder has ruptured, or if there are urethral stones that cannot be moved into the urinary bladder the patient will need to be evaluated by a surgeon for surgical intervention.

With the majority of cases those pesky obstructions can be successfully relieved with persistence, and trying a variety of techniques. Starting with adequate pain management helps set you up for success.  Consistent and gentle hydropulsion, changing positioning and urinary catheter types will help change pressures and perspective. Additional diagnostics like imaging and contrast studies will help gain more insight when the unblocking proves difficult.  And finally, always feel comfortable to ask a colleague for a fresh perspective, to refer, or call in the surgeon for their added expertise.



Cooper, E. S. “Controversies in the management of feline urethral obstruction”. J Vet Emerg Crit Care. 2015; 25 (1): 130-137.

O’Hearn, A. K. and B. D. Wright. “Coccygeal epidural with local anesthetic for catheterization and pain management in the treatment of feline urethral obstruction”. J Vet Emerg Crit Care. 2011; 21 (1): 50-52.

Segev, G., H. Livne, E. Ranen, and E. Lavy. “Urethral obstruction in cats: predisposing factors, clinical, clinicopathological characteristics and prognosis”. J Feline Med and Surg. 2011; 13: 101-108.

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