By Brennen McKenzie, MA, MSc, VMD, cVMA

One of the most common emergency conditions managed in general veterinary practice is urinary tract obstruction (UTO) in cats. Despite this, there is controversy about many aspects of UTO management, and even widely accepted practices are often based on limited or poor-quality evidence.^1,2

The annual incidence of UTO is reported between 0.5 percent and 1.5 percent, and it is most commonly seen in middle-aged cats, with males being the overwhelming majority of UTO patients.³

The proximate causes are most often crystalline uretheral plugs and uroliths, though obstruction may also be functional rather than mechanical in some cases.¹ The ultimate cause is less clear. Feline idiopathic cystitis (FIC) appears to be a factor in many UTO cases, but the etiology and pathogenesis of this syndrome are still not completely understood.^4,5

Several articles have reviewed the evidence for common UTO treatments.^1,2,5 There is no clearly optimal standard of care, and management varies with owner constraints and the resources and preferences of individual veterinarians. Nevertheless, evidence-based medicine encourages us to make decisions based on the basis of the best evidence we have, not the perfect evidence we wish we had. This involves setting a level of confidence in our conclusions and being prepared to change them as changes in the evidence warrant.

The purpose of this article is to provide a quick review of current evidence concerning some common UTO treatments about which there is some uncertainty or controversy.

Diagnostic imaging

Imaging, with radiographs or ultrasound, is often recommended as a component of UTO management due to the common presence of urolithiasis. One study, however, reported only 27 percent of UTO patients were imaged, suggesting this step may often be skipped in general practice settings.³

This same study reported 10 percent of cats imaged had urolithiasis, and other studies have reported findings of uroliths in 30 to 50 percent of UTO cases. This suggests many uroliths will be undetected if UTO is treated without imaging, potentially resulting in poorer treatment outcomes.

Catheterization

In general, relief of UTO by urethral catheterization is the most common practice. Management without catheterization as an alternative to avoid euthanasia when owners are not financially able to pursue catheterization and hospitalization has been reported.⁷

This approach is not suitable for cats with severe illness secondary to UTO, and success rates are lower than typically reported for treatment with catheterization, but the treatment was successful for the majority of cats in one study and should be considered as part of the spectrum of care options.^8,9 Catheterization, when performed, is successful in the vast majority of cats with UTO.³

Sedation vs. general anesthesia

For those patients treated by urethral catheterization, clinicians must choose whether to perform this procedure with the patient conscious, under sedation, or under general anesthesia. One study in the U.K.³ found only 3.6 percent of vets attempted catheterization in conscious cats.

The remainder were divided about evenly between sedation (~43 percent) and general anesthesia (~45 percent). It is worth noting only 1.9 percent of sedated cats were subsequently converted to general anesthesia, suggesting that sedation is likely sufficient in most cases.

Catheter size

There are theoretical arguments in favor of both larger urinary catheters (less likely to become obstructed or dislodged) and smaller catheters (less irritating to the urethra). Unfortunately, however, the limited research evidence on the question of catheter size is conflicting.

One retrospective observational study reported the risk of recurrence of UTO was lower in cats catheterized with smaller catheters.¹⁰ However, a similar prospective observational study did not find any such association between catheter size and recurrence of UTO.¹¹

Duration of catheterization

In general, the limited available evidence suggests indwelling urinary catheters yield a better outcome than single or intermittent catheterization.^6,12 The optimal duration for indwelling catheters is less clear.

Most studies suggest longer duration is associated with lower risk of recurrence,^11,12 but there are studies that have found no such relationship.¹⁰ It is likely individual patient factors influence the optimal duration of catheterization.¹²

Analgesia

UTO and its treatment are painful, and opioids are a mainstay of analgesic treatment.³ Buprenorphine is most commonly reported, though other opioids are also used. There is more controversy about the role of NSAIDs in managing UTO. A study in the U.K. reported meloxicam was used in 65.8 percent of UTO cases.³

However, meloxicam is licensed for chronic, as well as short-term, use in the U.K. and other European countries, and it is commonly offered to feline patients. In contrast, it is licensed only for short-term use in North America, and there is an explicit black box warning on the product in the U.S., which has discouraged use of this drug. The relatively recent approval of robenacoxib for cats without such a warning label, though, also only for short-term use, has provided an alternative NSAID, yet there is no research evidence directly comparing the safety of these drugs in cats with UTO.

Given many UTO cases involve FIC, which has a significant inflammatory component, it is plausible NSAID therapy would be beneficial in terms of analgesia and possibly control of the underlying cause of the obstruction. However, studies of the use of meloxicam in these patients have not found evidence this drug improves success or reduces recurrence.^10,13,14

One study also found no apparent reduction in pain with addition of meloxicam to other analgesic treatment, though the study did not involve objective assessment with a structured pain scale.¹³

It is, however, important to note none of these studies reported any adverse effects of meloxicam on clinical of laboratory measures, suggesting the theoretical risks of NSAIDs in properly selected UTO patients are uncommon.

Decompressive cystocentesis

Cystocentesis has been suggested both as an alternative and an aid to catheterization in UTO cases. However, puncturing a bladder with an abnormal wall raises the possibility of rupture or leakage. Fortunately, research suggests these complications are unlikely.

Cystocentesis was a key treatment in the study of UTO cats managed without catheterization, and uroabdomen did occur in a few of the treated cats, though bladder rupture was not observed.⁷ A retrospective study reported similar findings, with suspected uroabdomen based on radiographs, but no cases of bladder rupture observed.¹⁵ However, two prospective studies, including one randomized trial, did not find evidence of effusion or any other complications from cystocentesis in cats with UTO.^16,17

While the practice appears safe, unfortunately, the randomized trial also found no benefit, as cats treated with cystocentesis were not catheterized more easily or successfully than cats whose bladders were not decompressed.¹⁷

Muscle relaxants

Muscle relaxants are commonly used in cases of UTO with the intent of reducing the risk of re-obstruction due. There is no definitive answer to the question of whether these drugs actually improve patient outcomes. From a theoretical perspective, the most common drugs, prazosin and phenoxybenzamine, seem unlikely to be beneficial, as they target smooth muscle in the proximal urethra, and most obstructions occur in the distal urethra where skeletal muscle predominates.^1,2

While some evidence suggests outcomes are better when prazosin is used compared with phenoxybenzamine,¹⁰ a prospective randomized trial did not find a difference in outcomes between prazosin and placebo, though the trial was underpowered.¹⁸ Overall, the evidence supporting the widespread use of muscle relaxants in UTO is very weak.

Antibiotics

Antibiotics also appear to be used commonly in UTO patients despite a lack of compelling evidence for any benefit.⁶ Bacteriuria is found in few UTO patients (none in one study),^1,19 and in only a minority after catheterization (13 to 33 percent depending on the study).^13,19,20

This post-catheterization bacteriuria likely represents transient colonization rather than infection, and it is likely the vast majority of cases treated with antibiotics received no benefit.^1,2,6,21

Bladder lavage

Due to the common occurrence of blood, crystalline debris, and other material in the urine of cats with UTO, which may be a risk factor for reobstruction,²² bladder lavage after catheterization is sometimes recommended.² Only one prospective, randomized study has evaluated this practice, and no difference on short-term recurrence rate or duration of hospitalization was identified.²³

Bottom line

The majority of treatments commonly employed in feline UTO are based on limited and low-quality evidence. It is likely inpatient treatment with indwelling urinary catheters is more successful than the alternatives, but a spectrum of care options should be considered when this is not possible.

Antibiotics are very likely not useful, and the theory and evidence supporting use of muscle relaxants is not compelling. Analgesics are certainly indicated, and while opioids are the mainstay for short-term pain control, NSAIDs appear safe but of uncertain value.

As with most of the conditions veterinarians manage, we must make informed individual judgements about the best approach to treating each patient, considering the strength and limitations of the available evidence, proportioning our confidence in our choices to the strength of this evidence, and being ever ready to change course when better evidence suggests this is warranted.

Brennen McKenzie, MA, MSc, VMD, cVMA, discovered evidence-based veterinary medicine after attending the University of Pennsylvania School of Veterinary Medicine and working as a small animal general practice veterinarian. He has served as president of the Evidence-Based Veterinary Medicine Association and reaches out to the public through his SkeptVet blog, the Science-Based Medicine blog, and more. He is certified in medical acupuncture for veterinarians. Columnists' opinions do not necessarily reflect those of Veterinary Practice News.

References

1. Cooper ES. Controversies in the management of feline urethral obstruction. J Vet Emerg Crit Care (San Antonio). 2015;25(1):130-137. doi:10.1111/vec.12278
2. Cosford KL, Koo ST. In-hospital medical management of feline urethral obstruction: A review of recent clinical research. Can Vet J = La Rev Vet Can. 2020;61(6):595-604. http://www.ncbi.nlm.nih.gov/pubmed/32675811. Accessed April 17, 2022.
3. Beeston D, Humm K, Church DB, Brodbelt D, O'Neill DG. Occurrence and clinical management of urethral obstruction in male cats under primary veterinary care in the United Kingdom in 2016. J Vet Intern Med. 2022;36(2):599-608. doi:10.1111/jvim.16389
4. Forrester SD, Towell TL. Feline idiopathic cystitis. Vet Clin North Am Small Anim Pract. 2015;45(4):783-806. doi:10.1016/j.cvsm.2015.02.007
5. Jones E, Palmieri C, Thompson M, Jackson K, Allavena R. Feline Idiopathic Cystitis: Pathogenesis, Histopathology and Comparative Potential. J Comp Pathol. 2021;185:18-29. doi:10.1016/j.jcpa.2021.03.006
6. Beeston D, Humm K, Church DB, Brodbelt D, O'Neill DG. Occurrence and clinical management of urethral obstruction in male cats under primary veterinary care in the United Kingdom in 2016. J Vet Intern Med. 2022;36(2):599-608. doi:10.1111/jvim.16389
7. Cooper ES, Owens TJ, Chew DJ, Buffington CAT. A protocol for managing urethral obstruction in male cats without urethral catheterization. J Am Vet Med Assoc. 2010;237(11):1261-1266. doi:10.2460/javma.237.11.1261
8. Brown CR, Garrett LD, Gilles WK, et al. Spectrum of care: more than treatment options. J Am Vet Med Assoc. 2021;259(7):712-717. doi:10.2460/javma.259.7.712
9. Stull JW, Shelby JA, Bonnett BN, et al. Barriers and next steps to providing a spectrum of effective health care to companion animals. J Am Vet Med Assoc. 2018;253(11):1386-1389. doi:10.2460/javma.253.11.1386
10. Hetrick PF, Davidow EB. Initial treatment factors associated with feline urethral obstruction recurrence rate: 192 cases (2004–2010). J Am Vet Med Assoc. 2013;243(4):512-519. doi:10.2460/javma.243.4.512
11. Eisenberg BW, Waldrop JE, Allen SE, Brisson JO, Aloisio KM, Horton NJ. Evaluation of risk factors associated with recurrent obstruction in cats treated medically for urethral obstruction. J Am Vet Med Assoc. 2013;243(8):1140-1146. doi:10.2460/javma.243.8.1140
12. Seitz MA, Burkitt-Creedon JM, Drobatz KJ. Evaluation for association between indwelling urethral catheter placement and risk of recurrent urethral obstruction in cats. J Am Vet Med Assoc. 2018;252(12):1509-1520. doi:10.2460/javma.252.12.1509
13. Dorsch R, Zellner F, Schulz B, Sauter-Louis C, Hartmann K. Evaluation of meloxicam for the treatment of obstructive feline idiopathic cystitis. J Feline Med Surg. 2016;18(11):925-933. doi:10.1177/1098612X15621603
14. Nivy R, Segev G, Rimer D, Bruchim Y, Aroch I, Mazaki-Tovi M. A prospective randomized study of efficacy of 2 treatment protocols in preventing recurrence of clinical signs in 51 male cats with obstructive idiopathic cystitis. J Vet Intern Med. 2019;33(5):2117-2123. doi:10.1111/jvim.15594
15. Hall J, Hall K, Powell LL, Lulich J. Outcome of male cats managed for urethral obstruction with decompressive cystocentesis and urinary catheterization: 47 cats (2009-2012). J Vet Emerg Crit Care (San Antonio). 2015;25(2):256-262. doi:10.1111/vec.12254
16. Gerken KK, Cooper ES, Butler AL, Chew DJ. Association of abdominal effusion with a single decompressive cystocentesis prior to catheterization in male cats with urethral obstruction. J Vet Emerg Crit Care (San Antonio). 2020;30(1):11-17. doi:10.1111/vec.12914
17. Reineke EL, Cooper ES, Takacs JD, Suran JN, Drobatz KJ. Multicenter evaluation of decompressive cystocentesis in the treatment of cats with urethral obstruction. J Am Vet Med Assoc. 2021;258(5):483-492. doi:10.2460/javma.258.5.483
18. Reineke EL, Thomas EK, Syring RS, Savini J, Drobatz KJ. The effect of prazosin on outcome in feline urethral obstruction. J Vet Emerg Crit Care (San Antonio). 2017;27(4):387-396. doi:10.1111/vec.12611
19. Cooper ES, Lasley E, Daniels JB, Chew DJ. Incidence of bacteriuria at presentation and resulting from urinary catheterization in feline urethral obstruction. J Vet Emerg Crit Care (San Antonio). 2019;29(5):472-477. doi:10.1111/vec.12870
20. Hugonnard M, Chalvet-Monfray K, Dernis J, et al. Occurrence of bacteriuria in 18 catheterised cats with obstructive lower urinary tract disease: a pilot study. J Feline Med Surg. 2013;15(10):843-848. doi:10.1177/1098612X13477414
21. Weese JS, Blondeau JM, Boothe D, et al. Antimicrobial use guidelines for treatment of urinary tract disease in dogs and cats: antimicrobial guidelines working group of the international society for companion animal infectious diseases. Vet Med Int. 2011;2011:263768. doi:10.4061/2011/263768
22. Seitz MA, Burkitt-Creedon JM, Drobatz KJ. Evaluation for association between indwelling urethral catheter placement and risk of recurrent urethral obstruction in cats. J Am Vet Med Assoc. 2018;252(12):1509-1520. doi:10.2460/javma.252.12.1509
23. Dorsey TI, Monaghan KN, Respess M, et al. Effect of urinary bladder lavage on in-hospital recurrence of urethral obstruction and durations of urinary catheter retention and hospitalization for male cats. J Am Vet Med Assoc. 2019;254(4):483-486. doi:10.2460/javma.254.4.483