Feline lower urinary tract disease (FLUTD) describes a collection of conditions that can affect the bladder or urethra in cats and may be described as either obstructive (Figure 1) or non obstructive depending on the clinical symptoms presented. The annual incidence of FLUTD in British cats is believed to be around 1% (Gunn-Moore, 2003), with obstruction of the penile urethra accounting for 18–58% of these cases (Williams, 2009). Clinical signs of this condition include stranguria, dribbling of small amounts of urine, lethargy, inappetance and vomiting (Ford and Mazzaferro, 2006). A thorough knowledge of the treatment of urethral obstruction is therefore essential in order to care for each individual patient appropriately, however, some controversy surrounding treatment does exist. Two differing viewpoints have emerged over the years concerning treatment with the first being represented by Lekcharoensuk et al (2002) who found that medical management, mainly change in diet, was successful in treating this condition, reducing the need for surgical intervention. The second point of view disagrees somewhat with this position; Gerber et al (2008) conclude that although perineal urethrostomy does not entirely eliminate the risk of re-obstruction, the incidence of re-obstruction is reduced in cats who undergo urethrostomy compared with those cats who do not. The fact that such controversy exists concerning this issue is a healthy sign that more rigorous examination and studies are still occurring within the clinical and research communities.
Epidemiolical data
Although many of the epidemiological studies reviewed for this article contain a lot of useful data, almost all have utilized the non-specific terms of feline urological syndrome or FLUTD as the common denominator for the group of cats affected. Thus, as Osborne et al (1995) have identified the results of most of these studies must be interpreted in context of a combination of all types of FLUTD, rather than specific disorders. The results of these studies are, therefore, not directly relevant to urethral obstruction alone and should be viewed with caution as they may easily be misinterpreted. The classification of disorders together, however, has lessened over the years as more knowledge has been gathered regarding each condition. Nevertheless despite this increased knowledge the term idiopathic LUTD has to be used for cases where no underlying calculogenic (calculus forming), infectious, traumatic, neurogenic, iatrogenic (inadvertently caused by the veterinarian), congenital, neoplastic or drug or chemical-induced inflammatory cause can be identified. A study by Lekcharoensuk et al (2001a) revealed that 63% of cats analyzed were diagnosed with idiopathic LUTD, and other texts reviewed (Osborne et al, 1995; Gunn-Moore, 2003) are in agreement with the high incidence of this condition, highlighting the need for further studies in this area. To still have such a high prevalence of this disease caused by unknown factors is disappointing in today's veterinary community where much clinical research is being carried out.
Breed disposition data
It would appear from the literature that the domestic short-haired (DSH) cat is more pre-disposed to urethral obstruction than other breeds. However, critical analysis of studies undertaken suggests that this conclusion is a direct result of the higher percentage of DSH cats included in studies in comparison with other breeds, with figures exceeding 50% of cats studied in some cases (Gregory and Vasseur, 1983; Bass et al, 2005). As the population of DSH cats is in general greater than any other breed this finding may not be of any clinical significance, however, this is not mentioned in any of the studies carried out and could result in studies being misleading.
A retrospective study looking into breed predisposition to urethral obstruction by reviewing patient population over a set period of time at several clinics would be beneficial to determine whether the increased prevalence of urethral obstruction in DSH cats is clinically significant or not. This type of study could also help determine what, if any, factors predispose cats to the development of urethral obstruction which may inevitably assist in treatment and prevention (Figure 2).
Management outcome data
Much of the research carried out with regard to feline urethral obstruction is in the form of retrospective studies (Lekcharoensuk et al, 2001a, 2001b; Lekcharoensuk et al, 2002; Bass et al, 2005; Cannon et al, 2007) where data are retrieved from cats that have previously undergone treatment for lower urinary tract disease or more specifically perineal urethrostomy. Although this is a good way of obtaining data on many affected cats, all variables cannot be controlled and therefore results cannot be fully reliable.
Bass et al (2005) conducted a retrospective study on 59 cats in which they found that despite frequent complications, post-perineal urethrostomy 32.2% of the cats treated had a disease-free long-term (greater than 4 months) outcome. The reader of such a study needs to cautiously evaluate the conclusions drawn by the investigator. As LoBiondo-Wood and Haber (2002) state ‘finding naturally occurring groups of subjects who are similar in all aspects except for their exposure to the variable of interest is very difficult’. Also as retrospective studies look at events which took place in the past it is often difficult to obtain all the necessary information required to make results fully reliable and form definite conclusions.
Treatment option data
Surgical versus medical therapy to prevent urethral obstruction has not been evaluated by controlled prospective clinical studies (Osborne et al, 1991). It has been hypothesized that recurrent obstruction with matrix-struvite plugs could be minimized by dietary as well as surgical therapy. With a sample group of 30 cats with naturally occurring intraluminal urethral obstruction Osborne et al (1991) set out to compare the efficacy of perineal urethrostomy with management by use of a diet designed to dissolve struvite crystals. As the use of three controlled treatment groups reduces bias this study is one of the most valid and reliable reviewed. However with only 30 cats participating in the study (10 in each sample group) overall sample size is too small and to produce more significant results and a larger sample population would be required. Nevertheless the correct research approach was chosen for the goal being studied and all participants were accounted for at the end of the study. This study found that recurrence of urethral obstruction could be minimized with medical as well as surgical protocols and as a valid study given more investigation these results could be used to influence clinical practice today
Initial treatment of urethral obstruction
Treatment of urethral obstruction and its associated systemic signs are a true emergency as, if left untreated, this condition will eventually lead to renal failure and ultimately patient mortality. Authors such as Ford and Mazzaferro (2006) suggest that immediate treatment involves relief of the obstruction by catheterization or cystocentesis, however, the approach to these patients depends on their metabolic status on presentation. The correction of fluid, electrolyte, and acid–base disturbances by appropriate fluid therapy is essential as hyperkalaemia is the most life-threatening consequence of urinary tract obstruction (Scott-Moncrieff, 1996; Lee and Drobatz, 2003) with clinical signs such as weakness, bradycardia and reduced cardiac output. In a clinical trial carried out by Lee and Drobatz (2003) it was found that of the 223 cats with urethral obstruction included in this study 12% had potassium concentrations greater than 8.0 mmol/l. With the potassium range in a normal healthy cat at around 3.5–5.0 mmol/l and clinical signs occurring at levels of 7.5 mmol/l (Cannon 2000), the concentrations found in this study are at a life threatening level. It is, therefore, extremely important to treat this condition promptly to reduce the risk of patient mortality.
While the use of intravenous fluid therapy in the management of urethral obstruction is not questioned, the type of isotonic crystalloid fluid to be used in such cases has been the subject of debate (Drobatz and Cole, 2008). It is hypothesized that fluid choice in treatment of urethral obstruction makes no clinically significant difference to blood potassium levels from baseline, inferring that solutions containing potassium are still acceptable in treating hyperkalaemic patients. As a randomized prospective study this was a fair trial and the information gained from this would be of benefit to today's practitioners — it found that the use of a balanced electrolyte solution allowed a more rapid correction of blood acid–base status than 0.9% sodium chloride within the first 12 hours of fluid therapy.
Dietary management
Several methods of control and relief of urethral obstruction have been reported (Osborne et al, 1995;), but much of the current popular literature has looked at dietary management of post-obstruction cases with regard to dissolving matrix crystalline plugs and uroliths in cats (Funaba et al, 2003; Cannon et al, 2007). Dissolution can be achieved for struvite, urate and cystine uroliths, and is thought to be the method of choice for most animals without life-threatening signs of urolithiasis (Davies, 1996).
A large part of the literature concerned with urethral obstruction in male cats has tended to focus on the quantitative impact of diets designed for magnesium ammonium phosphate uroliths. Clinical studies have been reported that show restriction of dietary magnesium, increasing sodium consumption and promoting acidification of urine was successful in the dissolution and prevention of struvite uroliths (Osborne et al, 1991). However, one of the most interesting developments in veterinary urolithiasis research has been the recent change in the composition of stones recovered from cats. Certain studies have shown that these diets, designed to dissolve struvite, are now leading to a higher incidence of calcium oxalate uroliths instead which cannot be dissolved by dietary management (Lekcharoensuk et al, 2001b; Cannon et al, 2007). Therefore, while dietary therapy represents a cornerstone in the management of feline urethral obstruction it is not always curative.
Surgical treatment
Surgical intervention to treat urethral obstruction involves performing a urethrostomy, which is the creation of a permanent fistula into the urethra. Surgery is indicated to prevent recurrence of obstruction in the male cat or to treat obstruction that cannot be eliminated by catheterization (Fossum, 2007). Depending on the site of the obstruction urethrostomy can be prescrotal, scrotal, perineal, or prepubic, however, perineal urethrostomy is more routinely performed in cats (Fossum, 2007). The indications for and outcome of this type of surgery were reviewed in 2005 by Bass and colleagues who found that despite frequent complications many cats had a disease-free ‘long-term’ outcome post surgery. However, as these cats were only evaluated up to 4 months post surgery many long-term complications such as recurrent urinary tract infection and re-obstruction may have been missed and a longer period of evaluation would have lead to more reliable results.
In the late 1970s a study was carried out on 35 cats with a minimum follow up of 24 months post-perineal urethrostomy to determine whether bacteriuria and other complications developed post surgery (Gregory and Vassuer, 1983). The results of this study did not appear to have real clinical significance as although bacteriuria was identified all cats were asymptomatic and the owners were happy with progress. Overall, results may have been skewed; of the 151 records reviewed of cats that had undergone perineal urethrostomies only 35 (23%) were available for clinical examination. The study question proposed was not fully addressed as there was little mention of other complications encountered post surgery even though 11 cats suffered bouts of dysuria in the 2 year follow-up period examined. It would have been more fitting to focus fully on the incidence of bacteriuria alone as this is studied more in-depth throughout this article. The subject range was varied and all cats received the same diagnostic testing with objective analysis which helped eliminate bias. Despite this there are some flaws in sampling technique as not all cats had urine samples obtained by cystocentensis; three were obtained by midstream collection which could be a source of bacteria introduction. There is also no detail given on the initial source of obstruction which required surgery or severity of presenting clinical signs.
In 1977 Long published a paper in which he discussed a technique for perineal urethrostomy in the cat by creating a stoma in the pelvic rather than penile urethra. Since its diameter is bigger it was thought that this technique would have a greater success rate. This read more as a discussion than a research paper as it was almost fully descriptive lacking in the necessary analysis of results. With little information given on how patients were selected or how post-operative complications and findings were investigated the results must be viewed cautiously. As there were only 15 cases reported this figure is not sufficient to make generalizations to its success in the feline population as a whole.
Despite perineal urethrostomy being the most commonly described surgical procedure carried out in cats a study was undertaken to investigate the indications for and long-term outcome of prepubic urethrostomy (PPU) in 16 cats (Baines et al, 2001). With a high incidence of early (<6 months) and late (>6 months) complications it was concluded that PPU was a salvage procedure intended for use only if conventional perineal urethrostomy failed. However, with such a small sample group and several differing indications for PPU the overall results of this study are weak when cited with reference to management of obstructed cats.
Another research article evaluated the outcome of urethral obstruction in cats (Gerber et al, 2008); while carrying out their own literature review prior to undertaking this study the authors found that there were few data about patient prognosis. The sample studied consisted of 45 cats diagnosed with obstruction. Based on this study it was suggested that the long-term prognosis for cats with urethral obstruction was guarded with 51% of cats showing recurrent signs of LUTD, 36% re-obstructing and 23% being euthanased due to LUTD. They also found that although cases of obstruction have declined over the past 20 years there was no improvement in the prevention of re-obstruction in affected cats.
Conclusion
This literature review examined research conducted to date on the treatment of feline urethral obstruction. This included proposed dietary recommendations for the management of the disease and techniques for surgical intervention. Carrying out this review has highlighted the importance of literature reviews, as one piece of evidence taken in isolation is not sufficient on any given topic. The lack of a clear definition of obstruction and lack of system of reporting findings makes the true incidence of feline urethral obstruction difficult to diagnose. It is difficult, therefore, to summarize the literature on urethral obstruction in cats and not use the phrase that ‘more research is needed’. Many of the articles read, such as Lekcharoensuk et al (2001a), suggest in their discussions that further studies must be undertaken to fully understand areas regarding treatment and long-term outcomes for patients with urethral obstruction. What is clear from this review is that in the first incidence of urethral obstruction ideally medical management should be instigated if it is possible to relieve the blockage. For cats that repeatedly obstruct despite dietary and medical management, surgical intervention should be considered.
A careful review of the literature and research on this topic improves understanding of the treatment options available in order to provide the most appropriate care to our patients. While not being an actual research experiment, an extensive review of the current research and available literature on a given subject adds to the body of knowledge for evidence-based nursing care delivery.