This article describes seven steps for performing retrograde urohydropropulsion.
EDITOR' NOTE:Last month, in the first of two articles, retrograde urohydropropulsion was discussed as a technique for restoring urethral patency in dogs, usually with less chance of iatrogenic trauma. This second article describes seven steps for performing retrograde urohydropropulsion.
Perform appropriate diagnostic procedures to localize the sites of urethrolith(s). Evaluate their number, size, radiodensity and surface characteristics. Since uroliths rarely form in the urethra but migrate from the bladder lumen into the urethra, be sure to include the urinary bladder in the evaluation. Palpation of the posterior urethra (including palpation of the urethra per rectum) followed by appropriate survey or contrast radio-graphy should be performed to establish the site(s) and cause(s) of outflow obstruction.
Ultrasonography may be of value in evaluation of the urinary bladder. If the urethroliths become lodged in an unusual or unexpected location in context of the caudal aspect of the os penis, use contrast urethrography to rule out mural and/or extramural urethral lesions that are contributing to outflow obstruction. If the patient has signs of systemic illness, or if the history suggests prolonged outflow obstruction, pretreatment urine and blood samples should be obtained to assess renal function, systemic fluid, electrolyte and acid-base status.
Figure 1: Removal of urethrolith in a male dog by urohydropulsion. Dilation of the urethral lumen is achieved by injecting fluid with considerable pressure. Digital pressure applied to the external urethral orifice and the pelvic urethra has created a closed system.
If obstruction to urine outflow already has resulted in over-distension of the bladder lumen, it should be decompressed by cystocentesis. To prevent iatrogenic over-distension of the bladder, decompressive cystocentesis generally should be performed prior to urohydropropulsion.
Figure 2: Sudden release of digital pressure at the pelvic urethra and subsequent movement of fluid propelling the urethrolith toward the bladder lumen.
Some benefits of this are:
1) An uncontaminated representative urine sample suitable for analysis and culture is obtained.
2) Temporarily correcting the problem by decompressive cystocentesis provides a mechanism to ameliorate discomfort and adverse effects associated with post-renal azotemia.
3) Decompression of an over-distended urinary bladder and proximal urethra may decrease resistance to retrograde hydropropulsion of urethroliths back into the bladder lumen. Failure to decompress before the procedure can result in impaired ability to flush urethroliths into the urinary bladder (Table 1, p. 8S).
If excessive pressure is created in the over-distended bladder lumen, it will rupture. The potential risks of performing decompressive cystocentesis are that (a) it may result in extravasation of urine into the bladder wall and/or peritoneal cavity, and (b) it may injure the bladder wall or surrounding structures.
Although these complications could be severe in patients with a devitalized bladder wall, in our experience this has been a very uncommon exception rather than the rule, provided that the majority, but not all, of the urine is removed from the bladder before initiating urohydopropulsion.
Intra-peritoneal escape of a small quantity of urine through the pathway created by a 22-gauge hypodermic needle usually is of little consequence. The potential of trauma to the bladder and adjacent structures can be minimized by proper technique.
We are not advocating an "always or never" approach to decompressive cystocentesis. Clinical judgment is required regarding its use in each patient. However, it is preferable to decompress the urinary bladder by cystocentesis (saving an aliquot for appropriate diag-nostic tests) prior to performing retrograde urohydropulsion in patients likely to have adequate integrity of the bladder wall, and in which immediate over-distension of the bladder lumen, which predisposes to loss of urine into the bladder wall and peritoneal cavity, is prevented by serially performed decompressive cystocentesis.
Technique of decompressive cystocentesis : 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. After the needle is inserted into the bladder lumen, one individual should digitally immobilize the urinary bladder containing the tip of the 22-gauge needle, while another aspirates urine from the bladder lumen through flexible intravenous tubing into a large-capacity syringe. Gentle agitation of the distended bladder in an up-and-down motion prior to cystocentesis may disperse particulate matter or crystals throughout the urine, and thus facilitate their aspiration into the collection system.
The bladder should be emptied as completely as is consistent with atraumatic technique. Attempts to completely evacuate all urine from the bladder lumen are contra-indicated because this mistake predisposes the patient to iatrogenic trauma of the bladder mucosa and underlying tissues with the sharp point of the needle. Depending on the size of the dog, we typically allow about 15 to 20 ml of urine to remain in the bladder lumen.
In the event patency of the urethra is not established before the bladder fills with urine and fluid used to back-flush the urethra, decompressive cysto-centesis should be repeated before over-distension of the bladder lumen recurs. On occasion, we have used serial decompressive cystocentesis over a span of several days because of problems in restoring urethral patency.
Failure to properly lubricate the urethroliths prior to retrograde urohydropulsion may result in inability to flush them into the urinary bladder (Table 1).
A liberal quantity of a mixture of one part of sterilized physiologic saline solution (or a comparable parenteral isotonic fluid such as lactated Ringer's solution) to one part of aqueous lubricant should be injected through a catheter into the urethral lumen adjacent to the uroliths. This maneuver helps lubricate the surface of the urolith(s) and the urethral mucosa, which is often inflamed and swollen.
There may be some risk associated with injecting aqueous lubricants into the urinary tract of patients known to have tears in the wall of the urethra or urinary bladder. Aqueous lubricants have been implicated in the formation of periurethral granulomas in humans and rabbits. However, to date we have not recognized this problem following use of this technique in hundreds of dogs with obstructive urethroliths.
Some form of sedation or general anesthesia is required for most patients. Pharmacologic agents dependent on renal metabolism or excretion for inactivation and elimination from the body should be avoided.
If a patient is an anesthetic risk because of a uremic crisis, topical application of lidocaine gel to the urethral mucosa in combination with parenteral administration of a low dose of analgesic may provide adequate patient restraint.
General anesthesia should be used if uroliths cannot be removed from the urethra of non-anesthetized patients by urohydropropulsion. Inadequate pharmacologic control of patient discomfort may result in failure to flush the urethroliths into the bladder lumen (Table 1).
Appropriate precautions should be used for patients in renal failure because their sensitivity to general anesthesia may be increased.
In our experience, a combination of intramuscularly administered oxymorphone (0.1 to 0.2 mg/kg) followed by slow intravenous administration of propofol (an ultra-short-acting anesthetic) with dose titration to effect has been an excellent choice. Propofol is highly protein-bound; it is rapidly conjugated in the liver to inactive metabolites. However, neither sedation nor anesthesia produced by propofol is associated with complete relief of pain. Therefore propofol should be combined with oxymorphone. To avoid apnea, propofol should by be slowly administered by the intravenous route.
In addition, because propofol administration may be associated with depressant cardiovascular and respiratory effects (especially arterial hypotension), appropriate steps to correct dehydration of the patient should be initiated prior to anesthesia. If necessary, propofol anesthesia may be prolonged by frequent incremental intravenous injections, or by constant iv infusion of low doses.
Once urethral patency has been restored, the effects of oxymorphone can be antagonized with nalbuphine HCl ( 0.03 to 0.1 mg/kg IV) if continued analgesia is desired, or naloxone (0.002 to 0.02 mg/kg IV) if respiratory depression is of greater concern.
Inhalant anesthetics also may be considered to anesthetize the patient if the drugs are not dependent on the kidneys for inactivation and excretion from the body
To remove uroliths from male dogs by retrograde urohydropropulsion, we recommend this procedure :
1. 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.
2. Next, an assistant familiar with this procedure should gently insert a lubricated gloved index finger into the rectum. Firmly occlude the lumen of the pelvic urethra by applying digital pressure against the ischium through the ventral wall of the rectum.
3. A flexible catheter with an attached 20-ml to 35-ml syringe filled with sterilized saline should then be inserted into the lumen of the penile urethra via the external urethral orifice and advanced to the site of the urethroliths.
The penile urethra should be compressed around the shaft of the catheter by firm digital pressure. As a result of these steps, a portion of the urethra from the external urethral orifice to the bony pelvis becomes a closed system. Failure to properly occlude the pelvic and/or the distal-most portion urethral lumen will result in impaired ability to flush the urethroliths into the urinary bladder (Table 1).
4. Saline should be injected into the urethra until a marked increase in the diameter of the pelvic urethra is perceived by the assistant. Confirmation that the urethra has been markedly distended is important because 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.
Failure to create sufficient pressure in the urethral lumen often results in inability to flush the urethroliths back the urinary bladder (Table 1). The likelihood of rupture of the urethral lumen as a result of intraluminal pressure generated by this technique is remote because the path of least resistance for fluid is through the urethra into the bladder lumen and/or out the external urethral orifice.
However, caution must be used not to rupture the urinary bladder by over-distending the lumen with the flushing solution. Therefore, the size of the bladder should be monitored at appropriate intervals by abdominal palpation. If and when it becomes full, decompressive cystocentesis should be repeated.
5. At this point, the lumen of all portions of the isolated urethra, except that located in the ventral groove of the os penis, will be markedly dilated (Figure 1, p. 6S ). Dilation of the lumen of the segment of the urethra located in the ventral groove of the os penis is limited to that caused by stretching of the ventral portion of the urethral wall.
6. Next, digital pressure applied to the pelvic urethra (but not the penile urethra) should be rapidly released. Pressure should be maintained in the urethral lumen by continuing to inject saline by pushing the syringe barrel over the syringe plunger after the assistant has released digital pressure applied through the rectal wall. This step requires coordination between the two individuals performing the technique (Table 1). When properly coordinated, this step will propel the saline mixture and the urethroliths toward (or into) the bladder lumen (Figure 2, p. 7S).
Often, especially in cases where the uroliths have recently passed into the urethra, the urethroliths are easily flushed into the bladder lumen during the first attempt. However, in some situations, the uroliths do not move, or move only a short distance, before the pressure in the urethral lumen has dissipated. If this occurs, it may be necessary to repeat the procedure several times before all the uroliths reach the bladder lumen.
The position of the urolith(s) may be monitored either by means of: a) digital palpation of the perineal and pelvic urethra, b) a catheter carefully advanced through the urethra, and/or c) by means of radiography. If it is necessary to repeat the technique, accumulation of large amounts of saline and urine in the lumen of the bladder will necessitate repeating decompressive cystocentesis.
Appropriate care must be used to minimize trauma and pain to various components of the urinary tract, and to minimize the risk of iatrogenic urinary-tract infection. To minimize catheter-associated bacterial 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.
The need for prophylactic antibacterial therapy after retrograde urohydropropulsion must be determined on the basis of the status of the patient and retrospective evaluation of technique. If it is probable that the dog has ongoing UTI, or if restoration of urethral patency is associated with substantial trauma to, and/ or contamination of, the lower genitourinary tract, appropriate antimicrobial therapy should be initiated. Remember to obtain pretreatment urine samples for urinalysis and bacterial urine culture.
If, following restoration of urethral patency, the decision to use an in-dwelling transurethral catheter is being considered, the likelihood of inducing an iatrogenic bacterial infection must be considered.
Ascending migration of bacteria through the lumen of the catheter may be minimized by proper use of closed drainage systems that prevent reflux of urine from the collection receptacle back into the urinary tract.
However, bacteria may gain access to the bladder lumen by migrating through the space between the outside surface of the in-dwelling transurethral catheter and the surface of the urethral mucosa.
In this situation, the question is not whether a urinary-tract infection will occur, but rather when a urinary tract infection will occur.
Never forcefully advance a catheter through the lumen of the urethra. Trauma to the urethral wall is the usual consequence of use of excessive force, and may result in acute inflammatory swelling followed by formation of irreversible strictures.
Over-insertion of excessive lengths of catheter also should be avoided to minimize trauma to the bladder and/or to prevent the catheter from becoming knotted or entangled within the bladder and/or urethral lumens.
Once all of the stones are in the bladder, further treatment obviously should be considered.
Depending on the mineral composition of the urolith and a variety of other factors, some therapeutic options include medical dissolution, lithotripsy or cystotomy.
Contact our Web site for additional details (www.cvm.umn.edu. Click on the icon for Departments and Centers and then on the icon for the Minnesota Urolith Center).
by Carl A. Osborne DVM, PhD, Dipl. ACVIM, a diplomate of the American College of Veterinary Internal Medicine, is professor of medicine in the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota.