C.A. Osborne, DVM, PhD; J.P. Lulich, DVM, PhD
I. CANINE RETROGRADE UROHyDROPROPULSION
Urocystoliths are commonly voided into the urethra of male dogs where they often become lodged adjacent to the os penis. Once uroliths become lodged in the urethra of male dogs, it is very unlikely that they can be nonsurgically removed by voiding urohydropropulsion. However, urethral patency can be restored by flushing urethroliths back into the bladder lumen via retrograde urohydropropulsion. To be consistently successful, one must be familiar with all aspects of the technique. The objective of this review is to emphasize aspects of the technique that are frequently overlooked by colleagues who have been unsuccessful in attempting to restore urethral patency with this procedure.
Step 1. Verification and Localization of Urethroliths
Perform appropriate diagnostic procedures to localize the sites of the urethroliths, and to evaluate their number, size, and surface characteristics. Palpation of the entire urethra (including palpation per rectum), appropriate survey or contrast radiography, and/or ultrasonography should be performed to establish the site(s) and cause(s) of outflow obstruction.
Step 2. Decompressive Cystocentesis
If obstruction to urine outflow has resulted in overdistension of the urinary bladder, it should be decompressed by cystocentesis prior to urohydropropulsion . Failure to decompress an overdistended urinary bladder prior to retrograde urohydropulsion may result in impaired ability to flush urethroliths into the urinary bladder. We recommend that a 22 gauge needle be attached to a flexible intravenous extension set which in turn is attached to a large capacity syringe. One individual should digitally immobilize the 22-gauge needle in the bladder lumen, while another aspirates urine from the bladder lumen through the flexible tubing into the syringe. It is undesirable to attempt complete evacuation of the bladder lumen since this will allow the sharp point of the needle to damage the bladder wall. We recommend that 15 to 20 ml of urine be allowed to remain in the bladder.
Step 3. Lubrication of Urethroliths
A liberal quantity of a mixture of one or two parts sterilized physiologic saline solution to one part aqueous lubricant should be injected through a catheter into the urethral lumen adjacent to the uroliths. This maneuver helps to lubricate the urolith(s) and the urethral mucosa. Failure to lubricate the urethroliths prior to retrograde urohydropulsion may result in inability to flush them into the urinary bladder.
Step 4. Restraint and Anesthesia
Some form of sedation or general anesthesia is required for most patients. General anesthesia should be used if uroliths cannot be removed from the urethra of nonanesthetized patients by urohydropropulsion. Inadequate pharmacologic control of patient discomfort may result in failure to flush the urethroliths into the bladder lumen.
Step 5. Technique of Retrograde Urohydropropulsion
A. Inject a liberal quantity of a mixture of sterilized saline solution and aqueous lubricant through a flexible catheter into the urethral lumen adjacent to the uroliths.
B. Next an assistant should insert a gloved index finger into the rectum and firmly occlude the lumen of the pelvic urethra by applying digital pressure against the ischium through the ventral wall of the rectum. Failure to properly occlude the pelvic and/or distal urethral lumen will result in impaired ability to flush the urethroliths into the urinary bladder.
C. A flexible catheter with an attached 35 ml syringe filled with sterilized saline should then be inserted into the lumen of the urethra via the external urethral orifice and advanced to the site of the uroliths. CAUTION-Because pressure generated with the syringe is inversely proportional to the radius of the syringe barrel (law of LaPlace), use of a larger capacity syringe would result in a decrease in pressure generated by this system. The penile urethra should be compressed around the shaft of the catheter or cannula by digital pressure. As a result of these maneuvers, a portion of the urethra from the external urethral orifice to the bony pelvis becomes a closed system.
D. Saline in the syringe should be injected into the urethra until a marked increase in the diameter of the pelvic urethra is perceived by the assistant. If a flexible urethral catheter is used, we recommend that the top of the plunger be placed on the table so that the barrel of the syringe can be pushed down on the plunger. This maneuver will allow greater pressure to be generated within the isolated segment of the urethral lumen containing the uroliths. Distention of the urethra to its maximum capacity must be achieved before a sufficient degree of pressure can be created within the urethral lumen to advance the uroliths. Therefore, confirmation that the urethra has been markedly distended is of great importance. Failure to create sufficient pressure in the urethral lumen often results in inability to flush the urethroliths into the urinary bladder. The chance of rupture of the urethral lumen by intraluminal pressure generated by this technique is minimal since the path of least resistance for fluid is into the urinary bladder and/or out the external urethral orifice. However, caution must be used not to rupture the urinary bladder by overdistending it with saline. Bladder size should be periodically monitored by abdominal palpation. If necessary, decompressive cystocentesis should be repeated.
E. At the point when the lumen of all portions of the isolated urethra are markedly distended, digital pressure applied to the pelvic urethra (but not the penile urethra) should be rapidly released. Flow of fluid through the urethral lumen should be sustained by advancing the syringe plunger forward into the syringe barrel, even after the assistant has released digital pressure applied through the rectal wall. When properly coordinated by the two individuals performing the technique, the fluid flowing as a result of increased pressure will propel the urethroliths toward or into the urinary bladder. Sometimes all the urethroliths are rapidly return to the bladder lumen. However, in other situations, the uroliths only move a short distance before the flow of fluid under pressure has dissipated. When this occurs it is necessary to repeat the procedure until all the uroliths reach the bladder lumen. The position of the urolith(s) may be monitored by means of palpation of the perineal and pelvic urethra, with the aid of a urethral catheter, or by means of radiography. If it is necessary to repeat the technique, accumulation of saline in the lumen of the bladder will necessitate repeating decompressive cystocentesis.
Step 6. Minimize Catheter-Induced Trauma to the Urinary Tract, and Iatrogenic Urinary Tract Infection
To minimize catheter associated infection, catheters, lubricants, irrigating solutions, specula, and other instruments should be sterilized. However, because the distal portion of the urethra normally contains a commensal population of bacteria, it is impossible to aseptically catheterize the patient. Appropriate timing and selection of antimicrobic agents must also be considered.
II. NONSURGICAL REMOVAL OF UROLITHS BY VOIDING UROHYDROPROPULSION
Recently, we developed a nonsurgical technique to remove urocystoliths called voiding urohydropropulsion (Table 1). By taking advantage of the effect of gravity on urolith position in the urinary bladder and dilation of the urethral lumen during the voiding phase of micturition, this technique allows small urocystoliths to be flushed out of the urinary tract. During the past 5 years, we have used voiding urohydropropulsion to remove uroliths in hundreds of dogs. The following questions and answers are designed to enhance your ability to perform this technique.
How Can I Determine What Size Of Urolith Can Be Voided?
Proper selection of patients for voiding urohydropropulsion will enhance removal of urocystoliths. The relationship of the size, shape, and surface contour of urocystoliths to the luminal diameter of the urethra are important factors. Uroliths that are larger than the smallest diameter of any portion of the distended urethral lumen are unlikely to completely pass through the urethral lumen during voiding. As a guideline, we assume that smooth uroliths, less than 5 mm in diameter can be removed by voiding urohydropropulsion in any dog weighing more than 18pounds.
For Voiding Urohydropropulsion To Be Effective, How Much Fluid Should Be In The Bladder Lumen?
For voiding urohydropropulsion to be effective, the urinary bladder should be fully distended with urine or sterile isotonic solutions (lactated Ringers solution, physiologic saline, etc.). Distention of the bladder lumen enhances the voiding phase of micturition induced by digital compression through the abdominal wall. For most dogs, we fill the urinary bladder through an 8F, flexible catheter inserted into the bladder through the urethra. We inject enough fluid to maximally distend the bladder lumen as determined by palpating the bladder during filling. Sometimes we continue to fill the bladder until fluid begins to leak around the catheter. To maintain maximum bladder distension when this occurs, we occlude the distal urethra by compressing the vulva or prepuce between our thumb and forefinger.
If A Urolith Obstructs The Urethra, Is Voiding Urohydropropulsion Likely To Be Effective?
Voiding urohydropropulsion is unlikely to be effective in removing uroliths lodged in the urethra at the time of diagnosis.
How Can Voiding Urohydropropulsion Be Performed In Male Dogs?
The success of voiding urohydropropulsion is not dependent on the gender of patients. Rather, it is dependent on whether the size of uroliths will allow them to pass through urethral lumens. Because the diameter of the urethra in male dogs is smaller than female dogs, and because the os penis in male dogs restricts expansion of a portion of the urethral lumen, larger uroliths can be voided from female dogs compared to male dogs of equal size.
What If Uroliths Become Lodged In The Urethra During Voiding Urohydropropulsion?
If uroliths are too large to pass through the urethral lumen, they may become lodged in the urethra during voiding urohydropropulsion. When this occurs, uroliths should be flushed back into the bladder by retrograde urohydropropulsion. However, if the urinary bladder is distended with the fluid, retrograde urohydropropulsion may be difficult. Therefore, empty the bladder by decompressive cystocentesis before proceeding with the retrograde technique.
How Can I Learn To Perform Voiding Urohydropropulsion?
Prior to performing voiding urohydropropulsion, become proficient with techniques of transurethral catheterization, especially of female dogs and cats. Then, to minimize technical problems, perform your first voiding urohydropropulsion on a dog that you have scheduled for cystotomy. To facilitate a successful outcome, choose a medium size, female dog with relatively smooth uroliths equal to or less than 5mm in diameter. Anesthetize the patient just as if a cystotomy is going to be performed. However, first try voiding urohydropropulsion. If you have difficulty catheterizing the urethra, have difficulty in maximally distending the urinary bladder with fluid, or are unsuccessful in removing all uroliths, proceed with the surgery.
Table 1. Technique of Voiding Urohydropropulsion
Step 1--Anesthetize the patient.
Step 2--Distend the bladder with a sterile physiologic solution injected through a transurethral catheter.
Step 3--Remove the catheter. If fluid begins to pass through the urethra prematurely, occlude the distal urethra by digital compression of the vulva or penis.
Step 4--Position the patient so that the patient's vertebral column is approximately vertical.
Step 5--Gently agitate the bladder by palpation to promote gravitational movement of uroliths into the bladder neck.
Step 6--Apply steady digital pressure to the bladder to induce voiding. Once voiding begins, sustain bladder compression.