Subcutaneous Ureteral Bypass

Subcutaneous Ureteral Bypass by Dr Grace Wicks BVSc (hons) BVSc (MRT)

The invasiveness and morbidity associated with traditional ureteral surgeries has resulted in the interest and investigation of less invasive techniques. The Subcutaneous Ureteral Bypass (SUB) device is one example of a newer interventional radiology procedure that enables renal decompression.

A SUB device consists of a nephrostomy catheter connected to a cystostomy catheter via a port that can be accessed percutaneously. The device is therefore is conduit, enabling urine to flow through the catheters from the renal pelvis to the bladder.

Ureteral obstructions are challenging to both diagnose and treat. Uroliths are the most common cause of obstruction, however a variety of other conditions including strictures, ureteritis, mucus plugs, cellular or crystalline debris, blood clots, circumcaval ureters and neoplasia have been described.^1-3

Ureteral obstructions not only result in structural changes within the ureter and kidney but also a loss of renal function. Impact to renal function depends several factors including whether the obstruction is unilateral or bilateral, partial or complete and on the duration of obstruction. Experimental studies have demonstrated a progressive loss of renal recovery with increasing periods of obstruction. A near complete return of function occurred following relief of a four day ureteral obstruction. After 14 days of obstruction, GFR and tubular function returned to only 46% of the control levels after relief of obstruction.⁴ Others have reported complete recovery of concentrating ability is possible if the obstruction is alleviated within a one week. After four weeks of obstruction, permanent impairment of urinary concentrating ability occurs.⁵ Outside of the experimental setting, where healthy patients are used, clinical patients with preexisting renal disease are likely to have worse outcomes. This highlights the importance of a prompt diagnosis and early treatment to preserve as much renal function as possible.

One of the difficulties in diagnosing ureteral disease is that the clinical signs are commonly nonspecific. Cats may present with only inappetence, lethargy and/or weight loss.⁶ This differs from dogs who typically present with abnormalities with urination (incontinence, stranguria, hematuria, polyuria, pollakiuria) and systemic signs (vomiting, inappetance, depression, lethargy). This is likely due to the fact most dogs with a ureteral obstruction have associated pyelonephritis and cystitis.⁷ If uraemic, patients may present with vomiting, polyuria and polydipsia.² Physical examination may reveal renomegaly. Renal pain is more common in dogs with concurrent pyelonephritis.

Diagnosis of a ureteral obstruction typically involves serum biochemistry profile, complete blood count, urinalysis, urine culture and diagnostic imaging. Identification of the underlying cause of an ureteral obstruction should be sought to guide treatment and long term management. Azotemia is common at the time of diagnosis in both cats and dogs, even if the obstruction is unilateral.^6,8 This highlights the fact that preexisting chronic kidney disease is common in these patients. Cats are commonly anaemic.¹ Positive urine cultures are seen in 8-30% of cats^6,7 and 77% in dogs with uroliths.⁹ Sterile pyuria is also reported and likely due to the inflammatory processes that are initiated after ureteral obstruction.

Abdominal ultrasonography and radiography should be performed in suspected cases of ureteral obstruction. Ultrasound accurately evaluates for hydroureter, hydronephrosis and can locate the obstructive lesion. Additionally, it can assess for chronic changes in the kidneys and be used for monitoring of treatment. The sensitivity of abdominal radiographs in identifying feline ureteral calculi is 81% (versus 88% in dogs).^6,9 Severe hydroureter may also be seen. Computed Tomography can provide detailed images to identify the presence and location of calculi which is useful when traditional surgical therapies are planned. When a SUB is going to be placed, the location of the stones is less important because the entire ureter will be bypassed.⁷ Excretory urography/ intravenous pyelography may visualise the dilated ureter proximal to the site of obstruction, but opacification is often reduced when an obstruction is present. Other less frequently used imaging modalities include percutaneous antegrade pyelography, scintigraphy and measurement of renal resistive index with ultrasound.²

Historically, options to treat ureteral obstructions were restricted to either medical management or surgery (ureterotomy, ureteral resection and anastomosis, ureteroneocystostomy, ureteronephrectomy). Medical management should be initiated immediately following diagnosis of a ureteral obstruction to stabilise the patient. Intravenous fluid therapy should be carefully monitored to prevent overhydration. Antibiotics are recommended in dogs because the majority will have a urinary tract infection.¹⁰

Unstable patients (eg, hyperkalemic or becoming oliguric) should have intervention to decompress their kidneys. If immediate resolution (via ureterotomy, ureteroneocystostomy, stenting or SUB) is not possible then a nephrostomy tube should be considered. Haemodialysis is not readily available however aggressive medical management is usually adequate to stabilise patients for surgery.¹

In stable patients with ureteral obstructions, the decision to pursue surgery is not always straightforward. Medical management may result in the resolution of a urolith obstruction however only in the minority of cases. In addition to fluid diuresis; mannitol, amitriptyline, a-adrenergic blockade and glucagon can also be considered. Only 8-13% of cats were reported to have movement of their ureteral stones with aggressive medical management in one study.⁶ The ACVIM panel who created the Small Animal Consensus Recommendations on the Treatment and Prevention of Uroliths in Dogs and Cats reports that all ureteral obstructions, even partial obstructions, should be managed as emergencies.¹⁰ Surgery should be recommended when medical management fails, typically trialled for 24-72 hours.

The high incidence of chronic kidney disease and risk of contralateral obstruction also provides justification for surgery. Patient factors, surgeon expertise and availability of equipment play a role in decision making. Size does matter! The lumen of a normal cat ureter is 0.4mm! This makes feline ureteral surgery technically challenging. Some procedures performed in humans and dogs are unable to be performed in cats purely due to size e.g. percutaneous nephroureterolithotomy.

At VSS we been using SUBs with increased frequency for ureteral obstruction. According to the current ACVIM consensus recommendations, a SUB or ureteral stent are the first choice treatment options for obstructive ureteroliths in cats.¹⁰

The procedure involves a laparotomy. Fluoroscopy recommended to avoid complications however one case series reported successful placement without it.¹¹ The nephrostomy catheter is placed using a modified Seldinger technique. This involves placement of a 18 gauge catheter into the renal pelvis; through which a guidewire is passed. After catheter removal, the nephrostomy catheter is passed over the guidewire into the renal pelvis. The catheter is secured in place by locking the pigtail and placement of sterile tissue glue between the Dacron cuff and the renal capsule. The cystostomy catheter is placed surgically into the apex of the bladder through a pursestring suture. The catheter cuff and overlying silicone ring are secured to the serosal surface of the bladder with sutures and tissue glue. The abdominal muscle on the ipsilateral side is exposed lateral to the laparotomy site. The free ends of both catheters are tunnelled through the abdominal wall towards the port. The nephrostomy catheter end is connected to the caudal barb of the port and the cystostomy catheter end is connected to the cranial barb. This allows for gentle curving of the tubes to prevent kinking.

There are some obvious advantages to the SUB compared to others treatment techniques. Firstly, it can be used to treat all types of uretheral obstructions and pathologies regardless of location or number of ureteral lesions. Secondly, the cystotomy catheter enters the bladder at the apex which may result in less signs of dysuria compared to stents which enter through the ureteropelvic junction. The SUB port is accessed percutaneously which allows for flushing and urine sampling.

There is only limited information in the literature regarding complications and outcomes, mostly case reports and case series. Berent et al reported a 94% survival to discharge rate in a retrospective case series of 174 SUBs.¹² Median serum creatinine concentrations reduced from 6.6mg/dL at admission to 2.6mg/dL three months after SUB device placement. Postsurgical complications included occlusion with blood clots (8.1%), leakage (3.5%), and kinking of the tubing (4.6%). The most common long-term complication was catheter mineralisation (24.2%). The authors of this study note that since using tetrasodium EDTA (an antibiotic and anticoagulant) for the SUB flushes, the rate of mineralisation has reduced to < 4.5% (455 days of follow-up). UTIs developed in 24% of cats at some time after SUB device placement. Infections were successfully cleared with a single episode of appropriate an antimicrobial in 78% of cats in which treatment was pursued.

Kulendra et al reported a 10% mortality rate, 19% minor and 48% major complication rates.¹³ This study included cases that had the original SUB model placed; newer prototypes have addressed complications such as leaking, blockage and kinking. Additionally, current protocols that have been developed to avoid complications were not used in this study. For example, the flushing protocol using tetrasodium EDTA was not used, which may explain the high incidence of postoperative infections. Similarly, tissue plasminogen activator (TPA) can be used if the catheters become obstructed by blood clots. This also wasn’t used in this study. Therefore it is likely this study does not reflect complications encountered with current devices and protocols. Nonetheless, it highlights the fact new devices or protocols often require adjustment. The Nolfolk website reports of lower complication rates with their latest SUB 3.0 model.¹⁴ One major change in the design is the connection between the nephrostomy and cystotomy catheters is now within the abdomen. This aims to prevent kinking and catheter obstruction which is most likely to occur as the catheters cross the abdominal wall. If kinking here was to occur, drainage of urine through the nephrostomy and cytostomy catheters would still occur.

Livet et al 2016 reported improved outcomes with respect to hospitalisation duration, complications and mortality in cats treated with SUBs when compared to cats that underwent traditional ureteral surgeries.¹¹ 76.9% of SUB cats and 40% of cats that underwent traditional ureteral surgery were alive at followup 225 and 260 days, respectively. Only one SUB became obstructed and it resolved with flushing. Steinhaus et al reported reduced rates of reobstruction in cats treated with SUBs compared to stents (8% and 44% respectively).³ Perioperative survival was 7.8% which compares favourably to traditional surgical treatments (18-30%). In a study by Deroy et al there was a lower perioperative mortality rate (13%) in patients that had SUBs compared to those that were treated with ureteral stents (18%).¹⁵ The SUB group had a reduced rate of all complications in comparison to the stent group (lower urinary tract signs and obstruction). Horowitz et al also reported successful decompression and overall good survival in patients treated with SUBs.¹⁶ There was no difference in survival between cats who received stents or SUBs (88% survived to discharge).

Although the outcomes in many of the these studies are favourable, it appears lifelong management following placement of a SUB is required to prevent long term complications. Flushing is performed prior to discharge, at one week and one month post-operatively, then every three months thereafter. A Huber needle is used to prevent damage to the diaphragm of the port. Urine is obtained for analysis and culture every 3 months.

The owner must be made aware of the importance of rechecks, regular flushing and urine sampling. Treatment of an implant infection can be a lengthy and expensive process. Owner satisfaction was reported in one study.¹¹ 90% of owners were completely satisfied, 10% were mostly satisfied.

At this stage there is less known about the outcomes in dogs. One case series reported successful placement of 12 SUB devices.¹⁷ There was no peri-operative mortality, which compares favourably with other types of ureteral surgery (21- 27%) and medical management alone (33%).^6,9 Device mineralisation and infection were common complications. Once again, these cases were not treated with the tetrasodium EDTA flushing protocols.

In conclusion, collaboration between primary care veterinarians, medicine and surgery specialists will maximise outcomes in patients with ureteral obstructions. Early diagnosis and expedited renal decompression preserves renal function. Overall, SUBs are a good treatment option for ureteral obstructions in cats. In our experience, the placement is straightforward and procedure times are short. It can be used for all obstructive aetiologies and the outcomes compare favourably to other alternatives. The owner needs to be aware that lifelong management is required to minimise the risk of complications.

References

1. Palm CA, Culp WT. Nephroureteral Obstructions: The Use of Stents and Ureteral Bypass Systems for Renal Decompression. Vet Clin North Am Small Anim Pract. 2016;46:1183-92

2. Hardie EM, Kyles AE. Management of ureteral obstruction. Vet Clin North Am Small Anim Pract. 2004 Jul;34(4):989-1010. doi: 10.1016/j.cvsm.2004.03.008. PMID: 15223212.

3. Steinhaus J, Berent AC, Weisse C, Eatroff A, Donovan T, Haddad J, Bagley D. Clinical presentation and outcome of cats with circumcaval ureters associated with a ureteral obstruction. J Vet Intern Med. 2015 Jan;29(1):63-70

4. Wen JG, Frøkiaer J, Jørgensen TM, Djurhuus JC. Obstructive nephropathy: an update of the experimental research. Urol Res. 1999;27:29-39

5. Capelouto CC, Saltzman B. The pathophysiology of ureteral obstruction. J Endourol. 1993;7:93- 103

6. Kyles AE, Hardie EM, Wooden BG, Adin CA, Stone EA, Gregory CR, Mathews KG, Cowgill LD, Vaden S, Nyland TG, Ling GV. Management and outcome of cats with ureteral calculi: 153 cases (1984-2002). J Am Vet Med Assoc. 2005 Mar 15;226:937-44

7. Berent AC. Ureteral obstructions in dogs and cats: a review of traditional and new interventional diagnostic and therapeutic options. J Vet Emerg Crit Care 2011;21:86-103

8. Wormser C, Clarke DL, Aronson LR. Outcomes of ureteral surgery and ureteral stenting in cats: 117 cases (2006-2014). J Am Vet Med Assoc 2016;248:518-25

9. Snyder DM, Steffey MA, Mehler SJ, Drobatz KJ, Aronson LR. Diagnosis and surgical management of ureteral calculi in dogs: 16 cases (1990-2003). N Z Vet J. 2005 Feb;53(1):19-25

10. Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW, Osborne CA. ACVIM Small Animal Consensus Recommendations on the Treatment and Prevention of Uroliths in Dogs and Cats. J Vet Intern Med. 2016;30:1564-1574

11. Livet V, Pillard P, Goy-Thollot I, Maleca D, Cabon Q, Remy D, Fau D, Viguier É, Pouzot C, Carozzo C, Cachon T. Placement of subcutaneous ureteral bypasses without fluoroscopic guidance in cats with ureteral obstruction: 19 cases (2014-2016). J Feline Med Surg. 2017;19:1030-1039

12. Berent AC, Weisse CW, Bagley DH, Lamb K. Use of a subcutaneous ureteral bypass device for treatment of benign ureteral obstruction in cats: 174 ureters in 134 cats (2009-2015). J Am Vet Med Assoc. 2018;253:1309-1327

13. Kulendra, NJ, Borgeat, K, Syme, H, Dirrig, H. Halfacree, Z. Survival and complications in cats treated with subcutaneous ureteral bypass. J Small Anim Pract 2021;62: 4-11

14. Berent A, Weisse C. The SUB, a subcutaneous ureteral bypass device. A surgical guide. 2018 https://norfolkvetproducts.com/PDF/SUB/SUB2_Surgical_Guide_2018-03-email.pdf (accessed February 25, 2020).

15. Deroy C, Rossetti D, Ragetly G, Hernandez J, Poncet C. Comparison between double-pigtail ureteral stents and ureteral bypass devices for treatment of ureterolithiasis in cats. J Am Vet Med Assoc. 2017 ;251:429-437

16. Horowitz C, Berent A, Weisse C, Langston C, Bagley D. Predictors of outcome for cats with ureteral obstructions after interventional management using ureteral stents or a subcutaneous ureteral bypass device. J Feline Med Surg. 2013;15:1052-62

17. Milligan ML, Berent AC, Weisse CW, Lamb K, Toizer E. Outcome of SUB placement for the treatment of benign ureteral obstruction in dogs: nine dogs and 12 renal units (2013 to 2017). J Small Anim Pract. 2020;61:428-435