In male cats, UO is a life-threatening emergency that occurs as a complication of feline lower urinary tract disorders. Although UO in male cats occurs commonly, consensus regarding the most appropriate way to medically manage affected cats is lacking, as is evidence to formulate standardized recommendations.1 Consequently, clinicians are likely to manage affected cats on the basis of procedures with which they are familiar or that are routinely performed at their place of employment.
A frustrating complication associated with UO is recurrence of the obstruction, which can develop in the short or long term. Recurrence of UO can lead to prolonged or repeated hospitalization or surgical intervention (eg, perineal urethrostomy), resulting in an increase in morbidity, financial commitment, and risk for euthanasia.2–4 For male cats with UO, most clinicians recommend strategies for decreasing the risk for recurrence, such as dietary changes, pharmacological treatments, and environmental modifications, following initial treatment.1,5,6 Despite those recommendations, recurrence of UO is common, particularly in the short term while affected cats are hospitalized for the initial occurrence.
Some clinicians believe that lavaging the urinary bladder with saline (0.9% NaCl) solution at the time the urinary tract is unblocked and a urinary catheter is placed may help to remove or dilute debris, mucous plugs, urinary crystals, bacteria, or blood clots, thereby decreasing the risk for recurrence of the UO. To our knowledge, the efficacy of urinary bladder lavage on in-hospital recurrence of UO in male cats has not been evaluated. The objective of the study reported here was to evaluate the effect of urinary bladder lavage at the time of urinary tract catheterization for treatment of UO in male cats on the in-hospital recurrence rate of the condition and durations of urinary catheter retention and hospitalization. The null hypotheses were that urinary bladder lavage would have no effect on in-hospital UO recurrence, duration of urinary catheter retention, and duration of hospitalization.
Materials and Methods
Cats
All study procedures were reviewed and approved by the Cummings School of Veterinary Medicine Clinical Studies Review Committee. The study had a prospective design and involved client-owned cats. Owner consent was obtained for each cat prior to study enrollment.
Male cats that were examined by the emergency service at the Foster Hospital for Small Animals at Tufts University and determined to have UO on the basis of clinical history and results of a physical examination were considered for study enrollment. Cats with radiographic or ultrasonographic evidence of urolithiasis were subsequently excluded from the study. For each cat enrolled in the study, signalment, body weight, history of previous episodes of UO, and presence of macroscopic crystals or microscopic crystalluria during urinalysis were recorded.
Sample size calculation
Prior to study initiation, a sample size calculation was performed to determine the number of cats necessary for enrollment. Of primary interest was comparison of the in-hospital UO recurrence rate between cats that did and did not undergo urinary bladder lavage at the time of urethral catheterization to relieve the obstruction. Therefore, a test of 2 proportions with 1:1 allocation was used for the calculation. We wanted to be able to detect a 20% difference in UO recurrence between the 2 proportions (treatments). On the basis of our anecdotal experience and expert opinion, we estimated that 30% of male cats with UO would have recurrence of the condition while hospitalized for treatment of the initial UO episode. Therefore, for the purpose of the sample size calculation, we assumed that urinary bladder lavage would decrease the in-hospital UO recurrence rate to 10%; we also assumed an α of 0.05 and power of 80%. The calculation indicated that 62 cats would need to be assigned to each treatment group. We set a target sample size of 70 cats/treatment group to account for incomplete data collection or unexpected loss of patients following study enrollment.
Study design and patient management
All cats were enrolled in the study only once. Cats were randomly allocated to 1 of 2 treatment groups by selection of an envelope from a group of similar envelopes, each of which contained a slip of paper with the group assignment (flush or no flush). All cats were anesthetized, and the UO was relieved by passage of a rigid polypropylene open-ended tomcat cathetera through the urethra into the bladder. Physiologic saline (0.9% NaCl) solutiona was used for retrohydropulsion to facilitate removal of the UO at the discretion of the attending clinician. After the obstruction was removed, a 3.5F or 5F red rubber catheterb was inserted retrograde through the urethra into the urinary bladder and secured in situ. Then, for cats in the flush group, the bladder was lavaged with physiologic saline solution (volume range, 50 to 500 mL) until the retrieved fluid was clear, after which the urinary catheter was connected to a closed urinary collection system. For cats in the no-flush (control) group, the urinary catheter was connected to a closed urinary collection system immediately after placement without lavage of the urinary bladder. Following completion of the assigned treatment, the attending clinician for each cat completed a data collection form. Information collected included subjective assessment of the difficulty of urinary tract catheterization, which was scored on a scale of 1 to 4, where 1 = very easy, 2 = average, 3 = fairly hard, and 4 = very hard.
Subsequent patient care was not standardized. Attending clinicians were permitted to manage each patient at their discretion. In our hospital, management of male cats following alleviation of a UO typically includes administration of IV fluids, analgesics, and antispasmodics (usually prazosin) and housing in a quiet environment.
Definition of UO recurrence
Reoccurrence of UO was defined as the development of a firm urinary bladder following removal of the urinary catheter that did not resolve (ie, patient was unable to voluntarily express the bladder) after the patient was administered analgesics or anxiolytics and maintained in quiet surroundings. The general policy in our hospital was to give cats the benefit of doubt before diagnosing UO recurrence (recurrence was not diagnosed until cats had failed to respond [ie, not urinated] to analgesics, anxiolytics, and quiet surroundings). Typically, urinary catheters were electively removed between 4:00 and 8:00 am so patients could be observed for urination throughout the work day.
Statistical analysis
Descriptive statistics were generated, and results were summarized as proportions or the median (range) as appropriate. The data distribution for each continuous variable was assessed for normality by means of a Shapiro-Wilk test. None of the continuous variables were normally distributed; therefore, Wilcoxon rank sum tests were used to compare continuous variables between the 2 treatment groups. Binary and categorical variables were compared between the 2 treatment groups by means of χ2 tests. A post hoc subgroup analysis was performed to assess the effect of cystalluria on the in-hospital UO recurrence rate between the 2 groups. Values of P < 0.05 were considered significant for all analyses.
Results
Cats
One hundred thirty-seven cats were enrolled in the study; 69 cats were assigned to the flush group, and 68 cats were assigned to the no-flush group. The flush group included 5 sexually intact and 64 castrated males and had a median age of 5 years (range, 0.6 to 14 years) and weight of 6 kg (13.2 lb; range, 4 to 13 kg [8.8 to 28.6 lb]). The no-flush group included 2 sexually intact and 66 castrated males and had a median age of 5 years (range, 0.3 to 16 years) and weight of 5.7 kg (12.5 lb; range 3.4 to 6.9 kg [7.5 to 15.2 lb]). The ratio of sexually intact to castrated males (P = 0.226) and median age (P = 0.462) and weight (P = 0.136) did not differ significantly between the flush and no-flush groups. The proportion of cats with a previous history of UO in the flush group (11/69 [15.9%]) did not differ significantly (P = 0.419) from that in the no-flush group (9/68 [13.2%]). Likewise, among the cats that had a urinalysis performed, the proportion of cats with crystalluria in the flush group (27/58 [47%]) did not differ significantly (P = 0.244) from the proportion of cats with crystalluria in the no-flush group (32/54 [59%]).
Catheterization and treatment outcomes
For cats in the flush group, the median volume of saline solution used for urinary bladder lavage was 240 mL (range, 50 to 500 mL). Only 50 mL of saline solution was used during urinary bladder lavage for 2 cats. Both of those cats were described as having clear urine without visible grit or hemorrhage.
Data regarding the difficulty of urinary tract catheterization was available for 125 of the 137 (91.2%) study cats. Of those 125 cats, urinary tract catheterization was classified as very easy for 27 (21.6%), average for 63 (50.4%), fairly hard for 19 (15.2%), and very hard for 16 (12.8%). The frequency distribution for difficulty of urinary tract catheterization did not differ significantly (P = 0.582) between the flush and no-flush groups.
The in-hospital UO recurrence rate for the cats in the flush group (9/69 [13%]) did not differ significantly (P = 0.333) from the in-hospital UO recurrence rate for cats in the no-flush group (13/68 [19%]). Likewise, the proportion of cats with crystalluria that had UO recurrence did not differ significantly (P = 1.000) between the flush (6/27 [22%]) and no-flush (7/32 [22%]) groups.
The median duration of urinary catheter retention did not differ significantly (P = 0.338) between the flush (37 hours; range, 3 to 172 hours) and no-flush (36 hours; range, 1 to 117 hours) groups. Similarly, the median duration of hospitalization did not differ significantly (P = 0.231) between the flush (3 days; range, 0.5 to 12 days) and no-flush (3 days; range, 1 to 9 days) groups.
Discussion
In the present study, lavage of the urinary bladder of male cats following alleviation of UO and placement of a urinary catheter did not significantly decrease the in-hospital UO recurrence rate, duration of urinary catheter retention, or duration of hospitalization, compared with male cats that did not undergo urinary bladder lavage following alleviation of UO and placement of a urinary catheter. In another study,7 8 of 14 cats with recurrent UO were euthanized, with owner financial constraints reported as the most common reason for euthanasia. For male cats with a history of UO, in-home factors associated with a decrease in the risk for UO recurrence include increasing the availability of litter boxes and other forms of environmental enrichment, increasing patient water consumption, dietary modifications, pheromone therapy, and administration of anxiolytics and antispasmodics.1,5,6 Some of those in-home changes are difficult, if not impossible, to provide in a hospital setting, and in-hospital recurrence of UO is frustrating for both clinicians and owners. Although it seemed plausible that urinary bladder lavage would help dilute debris, crystals, and inflammatory cells that might contribute to UO recurrence, results of the present study failed to indicate that the procedure was beneficial for that purpose. Moreover, given that urinary bladder lavage requires additional materials and prolongs procedure and anesthesia times for male cats with UO, which translate to increased costs for owners, we cannot recommend it for routine treatment of male cats with UO.
The present study had multiple limitations. The overall in-hospital UO recurrence rate (22/137 [16%]) was low, and the in-hospital UO recurrence rate for cats in the no-flush (control) group was only two-thirds (13/68 [19%]) that expected for that group (30%). Therefore, the present study may have been underpowered. In a 2008 study,7 14 of 39 (36%) male cats had recurrence of UO within 14 days of the initial diagnosis, whereas in a 2013 study,5 only 10 of 68 (15%) male cats had recurrence of UO within 30 days of the initial diagnosis. During the a priori sample size calculation, we based the estimated UO recurrence rate for cats in the control group on those results,5,7 expert opinion, and our own clinical experience, and the study was powered to detect a 20% difference (30% vs 10%) in the in-hospital UO recurrence rate between the no-flush and flush groups. Increasing the number of cats enrolled in the study might have enhanced our ability to identify a < 20% difference in the UO recurrence rate between the 2 groups as statistically significant; however, conducting such a study might be challenging. For example, if we had assumed that the in-hospital UO recurrence rate for the control group was 19% and wanted to detect a 5% decrease in that rate, it would have been necessary to enroll 650 cats/group to achieve a study with a power of 80% and an α of 0.05.
Although the baseline characteristics and duration of urinary catheter retention did not differ between the flush and no-flush groups, it is possible there were unrecognized (or unevaluated) differences between the 2 groups that affected the outcome.
For example, the specific size of the indwelling red rubber catheter used was not recorded for each cat. Results of studies1,5,6 published after the present study was conducted indicate that use of a 5F versus 3.5F red rubber catheter in male cats with UO may increase the in-hospital UO recurrence rate. Unfortunately, missing data precluded a post hoc evaluation of the effect of urinary catheter size on rate of UO recurrence for the cats of the present study.
For the cats of the present study, the gross appearance of the urine at the time the urethra was unobstructed was not consistently recorded. Gross urine appearance might have affected the results of the present study because urine color is associated with severity of azotemia and presence of metabolic derangements (eg, hyperkalemia), which in turn can affect duration of hospitalization and cost of treatment.8 It is possible that urinary bladder lavage might be beneficial for cats with overt crystalluria and sludge in their urine.
Azotemia was also not evaluated as an independent risk factor for UO recurrence in the cats of the present study. Results of another study9 indicate that, in male cats with UO, azotemia is positively correlated with duration of hospitalization and treatment cost.
Aside from the assigned treatment, management of the cats of the present study was not standardized. Many of the study cats received prazosin (a sympatholytic) per hospital protocol, but its use was not consistently recorded. Additionally, IV fluid administration rates were not reliably recorded or adjusted, which could have affected urine concentration, pH, and presence or extent of crystalluria.
Another limitation of the present study was the fact that attending clinicians were aware of (ie, were not blinded to) the study treatment assigned to each cat. The unblinded nature of this study may have biased the clinicians’ assessments of outcome, although we believe that was unlikely because development of recurrent UO was not a subjective assessment.
Results of the present study suggested that, for male cats with UO, urinary bladder lavage at the time of urinary tract catheterization had no significant effect on in-hospital recurrence rate of the condition, duration of urinary catheter retention, or duration of hospitalization. Further studies are warranted to validate or refute the findings of this study. Such studies should involve a larger number of cats than in the present study and use standardized urinary catheter type and size and medication protocols. Studies should also be conducted of cats with UO and overt crystalluria.
Acknowledgments
No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
Presented, in part, in abstract form at the American College of Veterinary Internal Medicine Forum, Seattle, June 2013.
ABBREVIATIONS
| UO | Urethral obstruction |
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