Pathophysiology

Urethral obstructions can occur due to many reasons, including idiopathic feline lower urinary tract disease, urolithiasis, urethral plugs, spasm, oedema, strictures, and neoplasia. Urethral obstructions can lead to increased vesicular pressure, reducing the bladder wall viability. This can result in anaemia from microvascular injury, necrosis of the bladder wall, and in worst-case scenarios bladder rupture leading to uroabdomen. Prolonged urethral obstruction can result in increased renal pressure, decreased glomerular filtration rate and decreased renal blood flow; as a result, renal azotaemia leading to severe nausea, vomiting, diarrhoea, anorexia, dehydration and eventually hypovolaemic shock. As renal function is compromised, potassium excretion is reduced, resulting in hyperkalaemia and bradyarrhythmias. Hyperkalaemia and impaired renal function can both contribute to severe life-threatening metabolic acidosis.

Fluid Therapy/Metabolic Acidosis

Fluid therapy should focus on identifying and treating hypovolaemic shock if initially present; followed by maintenance, replacement, and ongoing losses (including post-obstructive diuresis). The type of fluid recommended is a balanced electrolyte solution such as Hartmann’s or Lactated Ringer’s, as this has shown to improved blood pH compared to 0.9% NaCl.^1,2 Volume of fluid should be considered carefully, as a recent study identified fluid overload after treatment for urethral obstruction in cats with no previous diagnosis of cardiac disease.³ In this study cats with fluid overload were more likely to have received a fluid bolus.

Hyperkalaemia

Table 1. Treatment for hyperkalaemia

Anaesthesia and Analgesia

Opioid analgesia should always be the first choice in cats with urethral obstructions (methadone or morphine for moderate to severe pain; and buprenorphine for mild to moderate pain). Non-steroidal anti-inflammatory drugs (NSAIDs) are contraindicated in cats with urethral obstructions until they are cardiovascularly stable, non-azotaemic, and eating. NSAIDs cannot be advocated at this stage for improvement in outcome as a recent study showed no difference in pain on abdominal palpation, recurrence rates or behaviour after being discharged home with NSAIDs, although a type II error may have occurred.⁴

As blocked cats can be critically ill, multimodal anaesthesia approach should be considered including local/regional anaesthetics. When using local/regional anaesthetics, always calculate the maximum dose you would administer systemically; particularly, lidocaine and related drugs can be cardiotoxic to cats at high doses. The author typically applies drops of lidocaine to the tip of the penis to minimise pain and spasm. Sterile lidocaine gel or sterile lubricant infused with lidocaine can be used to pass the urinary catheter. Coccygeal epidural has been described in cats,⁵ and more recently a study compared coccygeal epidural with bupivacaine, bupivacaine/morphine vs. no epidural in prospective double-blinded study⁶. This study showed a lower dose of propofol anaesthesia and longer time to rescue analgesia with use of epidural, although there was no difference in time or ease of urinary catheter placement.

Urinary Catheterisation

There are multiple options for urinary catheter selection which are listed in Table 2, although this is not an exhaustive list. One study compared the 3.5F Argyle catheter to the 3.5F red rubber catheters, and found no difference in recurrence rate.⁷ The size of urinary catheter has also been compared to investigate the recurrence rate, and it was found that size 3.5F (6.7%) had lower recurrence rates than 5F catheter (19%)⁸; although another study found no difference⁹.

Table 2

The ideal duration of indwelling urinary catheterisation is unknown. As re-obstruction rates are highest during the first 24 hours, the author usually leaves the indwelling urinary catheter in for 24–48 hours, and until the urine is clear, although careful not to leave the catheter in for too long as red urine was associated with higher recurrence rate in one study.¹⁰ If owners are cost constrained, once-off catheterisation can be performed to de-obstruct the urethra and flush the bladder with sterile saline, and be discharged home if stable. In one study, however, the recurrence rate of urethral obstruction was 3.7 times more likely when treated with once off catheterisation on an outpatient basis.¹⁰ Always keep a closed collection system to prevent secondary ascending UTIs. A commercial or sterile fluid bag can be used. Always keep the collection bag below the level of the patient to ensure constant flow and minimise ascending infections. When emptying the collection bag, always wash hands and wear gloves.

If passing the urethral catheter is challenging, there are a few tips you can try. One is to use an IV catheter with a single lumen tip to de-obstruct, as retrohydropulsion is more effective compared to using urinary catheters with side fenestrations. When performing retrohydropulsion, perform a rectal and occlude the urethra distal to the obstruction to increase the intraluminal pressure. You could also very gently massage the palpable plug or stone. Another tip, which has been published, is the use of 4 mL of atracurium besylate (0.5 mg/mL) flushed into the urethra prior to retrohydropulsion.¹¹

The debate about performing cystocentesis prior to urethral catheterisation is controversial. Cystocentesis will reduce the vesicular pressure, which could make urethral catheterisation and retrohydropulsion easier. However, one study did find peritoneal effusion to develop in 16% of cats after cystocentesis; however, none of the cats had clinical signs of uroabdomen and the nature of fluid was not identified.¹² Another study investigated managing urethral obstruction with cystocentesis alone, which resulted in spontaneous urination in 15/15 cats with 11 cats surviving to discharge.¹³ However, it is important to note that all cats selected for this study were not critically ill.

Pharmacotherapy

Prazosin, an α1 antagonist causing smooth muscle relaxation, has been advocated; however, only the proximal urethra consists of smooth muscle, while the distal portion where most urethral obstruction occurs has striated skeletal muscle. Some may argue for the use of prazosin, as the proximal urethra may get irritated from urethral catheterisation. Prazosin is advocated over phenoxybenzamine as phenoxybenzamine can take up to 1 week for clinical effect, and one study found less recurrence rates with prazosin compared to phenoxybenzamine.¹⁴ However, one study found no difference in recurrence rate between the use of prazosin and placebo.¹⁵

Antibiotics

Antibiotics should not be routinely administered as rates of UTI on presentation are only 0–40%. Urinary tract infections can occur secondary to urinary catheters, in which one study found 13% of cats having urinary tract infection 24 hours after catheter placement¹⁶; while another study found positive culture results in 16.7% of cats at 24 hours and 33% of cats 48 hours after placement¹⁷. Therefore, a urinalysis and culture and sensitivity should also be considered after removing the urinary catheter, with the most common isolates being Staphylococcus, E. coli, Streptococcus, and Pasteurella, which are sensitive to amoxicillin-clavulanic acid.

References

1.  Cunha MG, Freitas GC, Carregaro AB, et al. Renal and cardiorespiratory effects of treatment with lactated Ringer’s solution or physiologic saline (0.9% NaCl) solution in cats with experimentally induced urethral obstruction. Am J Vet Res. 2010;71:840–846.

2.  Drobatz KJ, Cole SG. The influence of crystalloid type on acid-base and electrolytes status of cats with urethral obstruction. J Vet Emerg Crit Care. 2008;18:355–361.

3.  Ostroski CJ, Drobatz KJ, Reineke EL. Retrospective evaluation of and risk factor analysis for presumed fluid overload in cats with urethral obstruction: 11 cases (2002–2012). J Vet Emerg Crit Care. 2017;27:561–568.

4.  Dorsch R, Zellner F, Schulz B, et al. Evaluation of meloxicam for the treatment of obstructive feline idiopathic cystitis. J Feline Med Surg. 2016;18(11):925–933.

5.  O’Hearn AK, Wright BD. Coccygeal epidural with local anesthetic for catheterization and pain management in the treatment of feline urethral obstruction. J Vet Emerg Crit Care. 2011;21(1):50–52.

6.  Pratt CL, Balakrishnan A, McGowen E, et al. A prospective randomized, double-blinded clinical study evaluating the efficacy and safety of bupivacaine versus morphine-bupivacaine in caudal epidurals in cats with urethral obstruction. J Vet Emerg Crit Care. 2020;30:170–178.

7.  Davidow EB. Retrospective evaluation of urinary indwelling catheter type in cats with urethral obstruction (January to December 2014): 91 cases. J Vet Emerg Crit Care. 2020;30:239–242.

8.  Hetrick PF, Davidow EB. Initial treatment factors associated with feline urethral obstruction recurrence rate: 192 cases (2002–2010). J Am Vet Med Assoc. 2013;243:512–519.

9.  Eisenberg B, Waldrop JE, Allen SE, et al. 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.

10.  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;252:1509–1520.

11.  Galluzzi E, De Rensis F, Menozzi A, et al. Effect of intraurethral administration of atracurium besylate in male cats with urethral plugs. J Small Anim Pract. 2012;53:411–415.

12.  Hall J, Hall K, Powell LL, et al. Outcome of male cats managed for urethral obstruction with decompressive cystocentesis and urinary catheterization: 47 cats (2009–2012). J Vet Emerg Crit Care. 2015;25:256–262.

13.  Cooper ES, Owens TJ, Chew DJ, et al. A protocol for managing urethral obstruction in malae cats without urethral catheterization. J Am Vet Med Assoc. 2010;237:1261–1266.

14.  Hetrick PF, Davidow EB. Initial treatment factors associated with feline urethral obstruction recurrence rate:192 cases (2004–2010). J Am Vet Med Assoc. 2013;243:512–519.

15.  Reineke EL, Thomas EK, Syring RS, et al. The effect of prazosin on outcome in feline urethral obstruction. J Vet Emerg Crit Care. 2017; 27(4):387–396.

16.  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;15:843–848.

17.  Cooper E, Lasley E, Daneils J, Chew D. Incidence of urinary tract infection at presentation and after urinary catheterization in feline urethral obstruction. J Vet Emerg Crit Care. 2019:1–6.

18.  Lee JA, Drobatz KJ. Characterization of the clinical characteristics, electrolytes, acid-base, and renal parameters in male cats with urethral obstruction. J Vet Emerg Crit Care. 2003;13(4):227–233.

19.  Cooper ES. Controversies in the management of feline urethral obstruction. J Vet Emerg Crit Care. 2015;25(1):130–137.

20.  Lee JA, Drobatz KJ. Historical and physical parameters as predictors of severe hyperkalemia in male cats with urethral obstruction. J Vet Emerg Crit Care. 2006;16(2):104–111.

21.  Beer KS, Drobatz KJ. Severe anemia in cats with urethral obstruction: 17 cases (2002–2011). J Vet Emerg Crit Care. 2016;26(3):393–397.

22.  Holroyd K, Humm K. Standards of care for feline urethral catheters in the UK. J Feline Med Surg. 2016;18(2):172–175.

23.  Cooper ES, Owens TJ, Chew DJ, et al. A protocol for managing urethral obstruction in male cats without urethral catheterization. J Am Vet Med Assoc. 2010;237:1261–1266.