Materials and Methods

Case selection criteria—Medical records of the Texas Veterinary Medical Center were reviewed to identify all male goats examined between January 2001 and January 2007 in which goats with urolithiasis were treated by means of percutaneous infusion of Walpole's solution.

Medical records review—Information obtained from medical records of cases included in the study consisted of signalment, duration of current complaint, concurrent illnesses, whether there was any history of urethral obstruction, and current diet. In addition, clinical findings at admission, including urethral patency, urine pH, diameter of the bladder as measured ultrasonographically, and presence of a urethral process, were recorded. Treatment and outcome variables recorded included other treatments administered, number of times Walpole's solution was infused, whether urethral obstruction resolved prior to discharge, duration of hospitalization, outcome (discharged alive or euthanized), and total cost of treatment and hospitalization. Treatment decisions were at the discretion of the attending veterinarian and included consideration of the relative value of the patient, intended use, financial commitment by the client, and clinician preferences. Owners of animals that were discharged were contacted by telephone to determine whether the animal was able to return to its intended use (ie, exhibition, production, or breeding) following treatment.

Treatment with Walpole's solution—For percutaneous infusion of Walpole's solution, goats were sedated with xylazine hydrochloride (0.22 mg/kg [0.1 mg/lb], IV) and restrained by an assistant in a sitting position to facilitate manipulation of the prepuce. The penis was exteriorized by grasping the shaft of the penis within the prepuce and applying pressure to exteriorize the tip while the prepuce was retracted. Once the tip of the penis was exposed, it was grasped with gauze sponges, allowing for examination of the urethral process and distal portion of the penis. If present, the urethral process was amputated with a scalpel. In animals with an intact frenulum, the urethral process was peeled away from the tip of the penis and amputated in a similar manner.

The goat was then placed in either left or right lateral recumbency, and the urinary bladder was identified with a 3.5-MHz, curved, linear (convex) ultrasound transducer. Following identification of the bladder, an approximately 6 × 6-cm area in the ventral aspect of the flank was aseptically prepared for cystocentesis. Ultrasound-guided cystocentesis was performed with an 18-gauge, 1.5-inch (3.8-cm) or 3.5-inch (8.9-cm) needle, depending on patient size and clinician preference. A 30-inch (76-cm) extension set was attached to the needle hub, and a 60-mL syringe was used to remove urine from the bladder. The amount of urine removed (120 to 500 mL) was adjusted such that an adequate volume of urine remained in the bladder to enable clear identification of the tip of the cystocentesis needle within the bladder lumen. Residual urine was allowed to remain in the bladder to ensure that the cystocentesis needle did not become dislodged from the bladder lumen or penetrate the far wall of the collapsed bladder. Urine pH was determined with a pH strip.^a

After urine was removed from the bladder, 50 mL of Walpole's solution^b was infused into the bladder and allowed to equilibrate for approximately 2 minutes. A urine sample was then obtained from the bladder via the cystocentesis needle, and pH was reevaluated after the first 10 mL to flush the extension set was discarded. Decompression of the bladder and administration of Walpole's solution were repeated in this manner until urine that was collected had a pH of 4 to 5. The volume of Walpole's solution required to achieve a pH of 4 to 5 varied, depending on the initial urine pH and residual amount of urine in the bladder. The cystocentesis needle was left in place during the entire process so that there was only a single injection site in the bladder during each treatment. Bladder size and needle placement were monitored ultrasonographically throughout the procedure.

Following completion of the procedure, tolazoline (2 mg/kg [0.9 mg/lb], IV) was administered to reverse the effects of xylazine. Animals with evidence of stranguria or signs of abdominal pain or distention and animals that did not have a normal stream of urine within 12 hours after treatment were reevaluated, and further treatment options (ie, surgical treatment or euthanasia) were discussed with the owner. Animals that were clinically improved but in which urethral obstruction had not completely resolved were considered candidates for retreatment with Walpole's solution if evidence of urinary tract leakage was not found. Urine calculi and crystals were not routinely collected for laboratory analysis.

In some animals, a 3.5-F polyurethane urinary catheter was used to determine the location of any obstruction within the urethra. A small volume (< 10 mL) of saline (0.9% NaCl) solution containing 1% lidocaine was instilled in an attempt to reduce urethral spasm and flush calculi from the urethra. Extreme caution was taken to prevent iatrogenic rupture of the urethra during this process.

Data analysis—Descriptive statistics (ie, mean and SD, median and range, or proportion) were calculated.

Results

Twenty-five goats met the criteria for inclusion in the study. There were 17 (68%) Boer goats, 5 (20%) crossbred goats, 2 (8%) Toggenburg goats, and 1 (4%) Angora goat. Eight of the 25 (32%) goats were sexually intact males, and 17 (68%) were castrated males. Information on age at the time of admission was available for 21 animals and ranged from 3.5 to 36 months (median, 9 months). Information on duration of clinical signs prior to examination, as reported by the owner, was available for 23 animals and ranged from 1 to 168 hours (median, 24 hours). Mean body weight at the time of admission was 38.7 ± 23.6 kg (85.2 ± 52.0 lb; range, 9.1 to 87.2 kg [20 to 192 lb]). All goats were fed concentrates, although type and quantity were not recorded, and only 9 of 24 goats were fed forage. Four animals had a history of previous urethral obstruction, whereas the remaining 21 animals did not have any history of previous urethral obstruction.

Urine pH determined at the time of admission was recorded for 20 animals and ranged from 7 to 10. In 18 animals, diameter of the urinary bladder was calculated ultrasonographically; diameter ranged from 5.3 to 12 cm (mean ± SD, 8.4 ± 1.0 cm). Two (8%) animals had concurrent illnesses at the time of admission including diarrhea (n = 1) and pneumonia (1). Urethral patency was recorded in 24 animals, with 14 (58%) animals having complete obstruction and 10 (42%) having partial obstruction. Clinical signs of partial urethral obstruction included stranguria, dribbling of urine, and a lack of a normal stream of urine during micturition. The urethral process was present and subsequently amputated in 18 of 24 (75%) animals. Four of the 6 animals without a urethral process at the time of admission had complete urethral obstruction.

Walpole's solution was infused once in 18 (72%) animals, twice in 6 (24%) animals, and 3 times in 1 (4%) animal. The amount of Walpole's solution required to achieve the target pH ranged from 50 to 250 mL.

Additional treatments that were administered included flunixin meglumine (23 goats [92%]), ammonium chloride (21 [84%]), antimicrobials (6 [24%]), and dexamethasone (3 [12%]). Duration of hospitalization ranged from 0.5 to 8 days (hospitalization time for animals treated on an outpatient basis was recorded as 0.5 days). Mean total cost of treatment was $210.21 ± 86.31 (range, $89.50 to $405.19). In 20 of the 25 (80%) goats, the urethral obstruction resolved, and the goat was discharged. The remaining 5 (20%) goats were euthanized because of unresolved urethral obstruction; owners of all 5 goats declined surgical treatment. Four of the 5 goats that were euthanized had received a single infusion of Walpole's solution, and 1 had received 2 infusions. At necropsy, all 5 animals had evidence of uroperitoneum and cystitis, and 4 had macroscopic lesions consistent with urethritis. Three goats had hydronephrosis, and 1 goat had microscopic evidence of reflux nephritis. Calculi from 3 of the goats were submitted for analysis, and 2 had struvite calculi, whereas 1 had magnesium carbonate calculi.

Urethral obstruction resolved in 14 of the 17 castrated males and in 6 of the 8 sexually intact males. It also resolved in both goats with concurrent illnesses at the time of admission. Urethral obstruction resolved in 16 of the 18 goats with a urethral process at the time of admission and in 3 of the 6 goats without a urethral process at the time of admission. Finally, urethral obstruction resolved in 11 of the 14 goats with complete obstruction and 8 of the 10 goats with partial obstruction.

Six of the 20 (30%) goats that were discharged were reexamined because of recurrence of urethral obstruction, including 1 goat that was reexamined twice because of recurrence. Time from discharge to recurrence was approximately 1 month, except in 2 goats in which time from discharge to recurrence was 8 days and 10 months, respectively. All 6 goats with a recurrence of urethral obstruction were treated with Walpole's solution at the time of recurrence, and urethral obstruction again resolved in 4 of the 6 (3 received a single infusion of Walpole's solution, and 1 received 2 infusions). The remaining 2 goats were euthanized because of persistent urethral obstruction despite 2 infusions of Walpole's solution. In the 1 goat with a third episode of urethral obstruction, the obstruction resolved after a single infusion of Walpole's solution.

Attempts were made to contact owners of all 20 animals that had been discharged following the initial treatment of urethral obstruction. However, 7 owners could not be reached by telephone. For the 13 owners that could be contacted, follow-up time ranged from 15.8 to 41.8 months. Nine of the 13 owners indicated that the animal had returned to its intended use. The remaining 4 owners indicated that the animal had not returned to its intended use; this included owners of the 2 goats that were euthanized after recurrence of urethral obstruction.

Discussion

Results of the present study suggested that ultrasound-guided cystocentesis in combination with percutaneous infusion of Walpole's solution may be a useful treatment in male goats with obstructive urolithiasis. However, recurrence was a concern, with urethral obstruction recurring in 6 of the 20 (30%; 95% confidence interval, 14% to 52%) goats that were discharged, and only 9 of the 13 goats for which long-term follow-up information was available were reportedly able to return to their intended use.

Although the urethral process is a common site of obstruction in goats with urolithiasis, amputation of the urethral process alone has been reported to relieve urine obstruction in only 66% of cases,¹¹ and resolution is frequently short-lived. For all goats in the present report, the urethral process, when present, was removed prior to infusion of Walpole's solution.

Use of perineal urethrostomy for treatment of goats with urolithiasis has been associated with a high recurrence rate,^11,29 and procedures such as tube cystostomy are likely to be more expensive than the procedure described in the present report because of the need for general anesthesia. In a previous report,²⁹ all 18 animals that underwent perineal urethrostomy survived to discharge; however, 15 of the 18 had a recurrence of urethral obstruction within 1 year after surgery. The long-term success rate was not determined in the present study. However, most of these animals were raised as exhibition or meat-producing animals, and would not have been expected to have a long life expectancy. For these animals, therefore, treatment would only have to relieve obstruction for a relatively short time (ie, weeks to months) to be considered successful. Our findings suggested that this technique may be useful in animals in which short-term resolution is the goal because it was noninvasive, resulted in resolution of the obstruction in a high proportion of cases, and did not require administration of drugs associated with substantial withdrawal times prior to slaughter. For example, the withdrawal time following IV administration of xylazine in meat goats is only 10 days, and the withdrawal time following IV administration of flunixin meglumine is only 4 days. Appropriate withdrawal times must be used, however, in animals treated with antimicrobials.

At the time of the present study, the client cost for 50 mL of Walpole's solution at our pharmacy was approximately $18.00. Because costs will vary from one hospital to the next, the costs of using Walpole's solution for treatment of urolithiasis will also vary. However, in our hospital, estimated costs for tube cystotomy in a goat with urolithiasis ranged from $1,500 to $2,000 at the time of the study.

In designing the present study, we had initially hoped to compare results in animals treated with Walpole's solution with results for animals treated with other methods. However, we were unable to do so because of differences between populations in regard to other factors potentially associated with resolution of the obstruction. Examination of records for 58 cases of urolithiasis during the study period revealed that most of the animals not treated with Walpole's solution were examined prior to the time that this treatment modality was adopted at our hospital, with the result that control animals in a study comparing goats that had or had not been treated with Walpole's solution would largely have consisted of historical control animals.

In our experience, the most frequently encountered complication following treatment with Walpole's solution was leakage of urine from puncture sites into the urinary bladder. The incidence of this complication, however, appears to have decreased as we became more familiar with the technique. During hospitalization, animals were monitored by means of physical examination for evidence of abdominal distention and by means of abdominal ultrasonography for evidence of abdominal effusion. Following discharge, owners were instructed to monitor animals for signs of illness, including fever, diarrhea, lethargy, stranguria, signs of abdominal pain, and anorexia, and to seek veterinary attention if any of these signs developed.

None of the goats in the present study that were discharged from the hospital had signs of clinically important uroperitoneum, even though all goats that underwent necropsy did have evidence of uroperitoneum. Ideally, cystocentesis would be performed only once to reduce the risk of inadvertent trauma to the bladder wall. Nevertheless, it is possible that animals with chronic, severe bladder irritation leading to compromise of the bladder wall may be more likely to have urine leakage, even from a single puncture site. Acidifying agents such as Walpole's solution have been reported to be irritating to mucosal linings, which may complicate the matter further, and several animals that underwent necropsy had gross evidence of cystitis. However, it would be difficult to determine whether cystitis was caused by the Walpole's solution or the underlying condition. Repeated cystocentesis was associated with intestinal adhesions in a previous study,¹⁸ but adhesions were not identified in the present study.

Importantly, in the present study, we could not determine how much of the response to treatment could be attributed to infusion of Walpole's solution alone and how much was the result of concurrent treatments, including administration of flunixin meglumine and ammonium chloride and amputation of the urethral process. Given our data, we cannot predict the long-term prognosis with use of this technique alone. Nor were we able to identify factors associated with a successful versus unsuccessful outcome.