Comparison between double-pigtail ureteral stents and ureteral bypass devices for treatment of ureterolithiasis in cats

Claire Deroy Department of Surgery, Veterinary Hospital Frégis, 94110 Arcueil, France.

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Diego Rossetti Department of Surgery, Veterinary Hospital Frégis, 94110 Arcueil, France.

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Guillaume Ragetly Department of Surgery, Veterinary Hospital Frégis, 94110 Arcueil, France.

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Juan Hernandez Department of Medicine, Veterinary Hospital Frégis, 94110 Arcueil, France.

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Cyrill Poncet Department of Surgery, Veterinary Hospital Frégis, 94110 Arcueil, France.

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Abstract

OBJECTIVE To compare the complication rates and outcomes in cats with ureteral obstruction treated by placement of double-pigtail ureteral stents or ureteral bypass (UB) devices.

DESIGN Retrospective cohort study.

ANIMALS Cats with unilateral or bilateral ureterolithiasis that received double-pigtail ureteral stents (30 stents in 27 cats; stent group) or UB devices (30 devices in 23 cats; UB group).

PROCEDURES Medical records were reviewed to collect data on signalment, clinical signs, serum biochemical data, surgical procedure, duration of hospitalization, complications, and follow-up (≥ 6 months after placement) information. Outcomes were compared between device types.

RESULTS Median durations of surgery and hospitalization were significantly longer in the stent versus UB group. Perioperative mortality rate was 18% (5/27) in the stent group and 13% (3/23) in the UB group. Median survival time was shorter in the stent versus UB group. Stent placement was associated with a greater risk of lower urinary tract–related signs, such as hematuria (52% [14/27]) and pollakiuria or stranguria (48% [13/27]). The risk of device occlusion was also greater in the stent (26% [7/27]) versus UB (4% [1/23]) group. The percentage of cats requiring additional procedures to treat complications was greater in the stent (44%; complications included uroabdomen, stent occlusion, and refractory cystitis) versus UB (9%; complications included UB occlusion and urethral obstruction) group.

CONCLUSIONS AND CLINICAL RELEVANCE Although the benefits of stent placement in the treatment of ureteral obstruction in cats have been established, results suggested that cats treated with UB devices had a lower risk of complications and a longer survival time than those treated with double-pigtail ureteral stents.

Abstract

OBJECTIVE To compare the complication rates and outcomes in cats with ureteral obstruction treated by placement of double-pigtail ureteral stents or ureteral bypass (UB) devices.

DESIGN Retrospective cohort study.

ANIMALS Cats with unilateral or bilateral ureterolithiasis that received double-pigtail ureteral stents (30 stents in 27 cats; stent group) or UB devices (30 devices in 23 cats; UB group).

PROCEDURES Medical records were reviewed to collect data on signalment, clinical signs, serum biochemical data, surgical procedure, duration of hospitalization, complications, and follow-up (≥ 6 months after placement) information. Outcomes were compared between device types.

RESULTS Median durations of surgery and hospitalization were significantly longer in the stent versus UB group. Perioperative mortality rate was 18% (5/27) in the stent group and 13% (3/23) in the UB group. Median survival time was shorter in the stent versus UB group. Stent placement was associated with a greater risk of lower urinary tract–related signs, such as hematuria (52% [14/27]) and pollakiuria or stranguria (48% [13/27]). The risk of device occlusion was also greater in the stent (26% [7/27]) versus UB (4% [1/23]) group. The percentage of cats requiring additional procedures to treat complications was greater in the stent (44%; complications included uroabdomen, stent occlusion, and refractory cystitis) versus UB (9%; complications included UB occlusion and urethral obstruction) group.

CONCLUSIONS AND CLINICAL RELEVANCE Although the benefits of stent placement in the treatment of ureteral obstruction in cats have been established, results suggested that cats treated with UB devices had a lower risk of complications and a longer survival time than those treated with double-pigtail ureteral stents.

Ureteral obstruction is a challenging problem and important cause of acute and chronic kidney disease in cats. Intraluminal obstruction may occur as a result of ureteroliths, blood clots, mucous plugs, or other intraluminal debris.1 Ureteroliths resulting from migration of nephroliths or nephrolith fragments into the ureter are the most common cause of obstruction in cats; > 98% of ureteroliths contain calcium oxalate.2,3 The diagnosis of ureterolithiasis should be made early because ureteral obstruction can have serious consequences, leading to irreversible sequelae in the renal parenchyma.

In the past 30 years, treatment options for ureterolithiasis in cats have been restricted to medical management or surgical intervention (eg, ureterotomy, retrograde flushing of calculi into the renal pelvis followed by pyelolithotomy, ureteronephrectomy, or neoureterocystostomy).2,4 Medical management relieves the obstruction, with reported success rates ranging from 8% to 17%.4,5 Studies4,5 have shown a decrease in the degree of azotemia in 30% of cats with ureterolithiasis 1 month after medical management began and a mortality rate prior to hospital discharge of 33% with medical management alone. Typically, cats with evidence of complete ureteral obstruction or worsening azotemia should be treated with surgery, which is more successful than medical management.4

The optimal duration of medical management before a decision is made to pursue surgery has not been determined for cats; however, early stabilization and surgical decompression are likely indicated to maintain kidney function.4 Traditional surgical procedures for cats with ureterolithiasis are associated with an 18% to 39% mortality rate prior to hospital discharge.2,4,6 Surgical complications include urinary leakage resulting in uroabdomen, persistent ureteral obstruction due to edema, recurrence of obstructive calculi, stricture formation at the surgical site, and renal failure.2,4,6

In human medicine, improvements in ureteroscopy, ureteral stent placement, extracorporeal shockwave lithotripsy, and laparoscopy have made minimally invasive management the treatment of choice when dealing with ureterolithiasis.7–11 Ureteral stents and UB devices are an integral part of human urological practice, with the potential to relieve obstructions.7–12 Because the luminal diameter of ureters in cats is approximately 0.4 mm,5 available options for treatment have been limited, and management of ureteral obstruction has evolved to include placement of DPU stents or UB devices. Such devices allow urine to bypass the ureteral obstruction at the site of the ureterolith and prevent additional renal damage from obstructive uropathy, while theoretically avoiding some of the complications associated with traditional surgical interventions.13–16

Reports of the use of ureteral stents and UB devices for cats with ureteral obstruction are limited in the veterinary literature. Reported perioperative mortality rates range from 8% to 16% after placement of stents and UB devices,13–16 and ureteral stent placement is associated with high rates of perioperative and long-term complications.13–16 Documentation of outcomes, particularly long-term outcomes, for cats with ureterolithiasis treated with a UB device is also lacking. Comparisons of clinical outcomes after placement of ureteral stents and UB devices in cats with ureterolithiasis have not yet been reported, to the authors' knowledge.

The purpose of the study reported here was to determine the clinical signs, preoperative and postoperative management approaches, and short and long-term outcomes for cats with ureterolithiasis undergoing placement of DPU stents or UB devices and to compare complication rates and outcomes between the 2 treatment options. We hypothesized that use of UB devices would result in lower incidences of clinically relevant intraoperative and postoperative complications, a higher rate of survival to hospital discharge, and a longer survival time than use of DPU stents.

Materials and Methods

Cats

Medical records of cats admitted to the Veterinary Hospital Frégis in Arcueil, France, were reviewed to identify cats with a diagnosis of obstructive ureterolithiasis that underwent placement of a DPU stent or UB device between February 2011 and May 2015. Only cats with complete records regarding signalment, history, initial complaint, physical examination findings, serum biochemical data, procedural information, duration of hospitalization, and intraoperative and postoperative complications and a minimum postoperative follow-up period of 6 months were included. Cats with insufficient data for all required medical variables were excluded, as were cats discharged from the hospital with a postoperative follow-up period < 6 months. The diagnosis of obstructive ureterolithiasis was based on findings of abdominal ultrasonography (ie, hydronephrosis-associated hydroureter and identification of ≥ 1 ureterolith). Data were also collected regarding transverse-plane measurements of the renal pelvis and ureteral dilation on the affected side and the suspected cause of ureteral obstruction as suggested by ultrasonographic findings.

Surgical treatment

Cats with ureteral obstruction were grouped by surgical technique used (placement of a DPU stent or UB device). All cats admitted to the hospital before the advent of the UB device (ie, between 2011 and 2013) received a DPU stent. For all other cats, choice of surgical procedure was made on the basis of the cause and location of ureteral disease. During the study period, a DPU stent or UB device was placed in cats with ureterolith-induced obstruction, and a UB device was placed if the dilated renal pelvis exceeded 3 mm in diameter. Whenever possible, cats were treated surgically following a medical management period of at least 24 hours in an attempt to achieve successful spontaneous stone passage, unless medical management was contraindicated.

In preparation for surgery, cats received morphinea (0.2 mg/kg [0.09 mg/lb], IM) and midazolamb (0.2 mg/kg, IV). General anesthesia was induced with propofolc and maintained with isofluraned in oxygen. Surgery was performed by board-certified surgeons (CP and GR) and, for UB device placement, by a third-year surgical resident, all of whom used an open surgical approach without the aid of fluoroscopy. Surgeons performed a complete abdominal exploration, and any abnormalities were noted. Affected ureters were located, and the site of obstruction was identified.

For cats in which stents were used, a 2.5F multifenestrated polyurethane DPU stente was implanted into the ureter over a guidewire in an antegrade (preferred approach) or retrograde fashion. The proximal ureter was dissected free from the surrounding tissue in the retroperitoneal space. For cats in the other group, a UB devicef that included a 6.5F locking-loop catheter and 7F catheter was placed as a nephrostomy and cystostomy tube, respectively. After insertion into the renal pelvis and bladder, catheters were subcutaneously connected by a connector (shunting port). The locking-loop nephrostomy catheter was not placed under fluoroscopic guidance, and the ureter was not isolated. Data were recorded regarding procedure type, side affected (unilateral or bilateral), procedure duration, and intraoperative complications.

Postoperative radiography was performed to ensure that all DPU stents and UB devices had been placed correctly (Figure 1). For cats in the UB group, proper catheter placement in the kidney and bladder and absence of urine leakage or catheter kinking were confirmed by contrast medium injection. A Huber needleg was used to inject slowly through the connector 3 mL of diluted (1:1) iohexol,h followed by 3 mL of sterile saline (0.95% NaCl) solution to flush the contrast medium from the catheter. All cats received an injectable opioid (buprenorphine,i 0.015 mg/kg [0.007 mg/lb], IV) for postoperative pain control. Criteria for safe discharge from the hospital included good clinical condition and appetite as well as an unremarkable serum creatinine concentration. Cats were discharged with a multicare urinary diet.j

Figure 1—
Figure 1—

Lateral radiographic views of the abdomen of 2 cats with urological obstruction. A—Postsurgical plain radiographic view showing placement of a DPU stent to bypass nephroliths and ureteroliths (arrow). B—Contrast-enhanced radiographic view obtained after positioning of a UB device and injection of contrast medium into the device. The UB device included a locking-loop kidney catheter (black arrows), shunting port (asterisk), and bladder catheter (white arrows).

Citation: Journal of the American Veterinary Medical Association 251, 4; 10.2460/javma.251.4.429

Complications

Perioperative data (within 1 week after device placement) and short-term (between 1 week and 1 month after device placement) and long-term (> 1 month after the procedure) outcome data were collected, including complications, serum biochemical values (measured in the immediate postoperative period, daily until hospital discharge, and 1, 3, 6, and 12 months after surgery), duration of hospitalization, whether the cat survived to discharge, and overall survival time. The UB devices were flushed with ultrasonographic guidance every 3 to 4 months in accordance with the recommendations of the device manufacturer.

Follow-up information was obtained from the medical records and via a questionnaire provided to cat owners and referring veterinarians by one of the investigators (CD). The questionnaire was designed on the basis of that used in a previous study.14 Respondents were asked to provide information on the presence and duration of postoperative clinical signs (including urinary tract–related signs), quality of life, and frequency of urination. Signs of dysuria were classified as mild (cat urinates 2 to 5 times/d), moderate (cat urinates 5 to 10 times/d), or severe (cat urinates > 10 times/d).14 For cats that died during the follow-up period, cause of death was recorded.

Statistical analysis

Statistical analysis was performed by use of statistical software.k The Mann-Whitney rank sum test with nonparametric continuity correction was performed to compare values of quantitative data between treatment groups (DPU stent or UB device). Numerical data are reported as median and range. Distributions of qualitative variables were compared between groups by means of the Fisher exact test. To compare the number of times per day cats urinated, the Kruskal-Wallis rank sum test was performed. Survival times were compared between groups with the Kaplan-Meier method and log-rank test for equality over strata. Cats that were still alive at the time of the analysis were censored at the date of final follow-up. Values of P < 0.05 were considered significant.

Results

Cats

Thirty DPU stents were placed in 27 cats between February 2011 and October 2013, and 30 UB devices were placed in 23 cats between September 2013 and May 2015. All cats had unilateral or bilateral obstructive ureterolithiasis. During these periods, 109 cats with cystolith ureteral obstruction were evaluated at the hospital; 15 (14%) cats underwent successful medical management, 3 (3%) underwent ureterotomy, 32 (29%) were euthanized at the owner's request because of the poor prognosis (before or after a medical management attempt), and 9 (8%) had surgical treatment refused by the owner and were returned to the referring veterinarian. These 59 cats were excluded from the study.

Twenty-five (50%) of the included cats were neutered males (13 [48% of group total] in the stent group and 12 [52% of group total] in the UB group), 23 (46%) were spayed females (14 [52% of group total] in the stent group and 9 [39% of group total] in the UB group), and 2 (4%) were sexually intact males (2 ([9% of group total] in the UB group). Median age was 5 years (range, 1.5 to 16 years; Table 1). The 2 most common breeds were domestic shorthair (12 [44% of group total] in the stent group and 16 [70% of group total] in the UB group) and Birman (6 [22% of group total] in the stent group and 3 [13% of group total] in the UB group). Other breeds included Persian (n = 4), British Shorthair (3), Siamese (2), Scottish Fold (1), Chartreux (1), Russian Blue (1), and Maine Coon (1).

Table 1—

Median (range) age, body weight, and ultrasonographic measurements of cats with obstructive ureterolithiasis treated by placement of a DPU stent (30 stents in 27 cats; stent group) or UB device (30 devices in 23 cats; UB group).

CharacteristicStent groupUB groupP value
Age (y)5 (2–14)5 (1.5–16)0.71
Body weight (kg)3.7 (2.1–7.0)4.2 (2.0–7.0)0.29
Renal pelvic diameter (mm)12 (4–40)10 (1–25)0.09
Ureteral diameter (mm)3.0 (2.5–8.0)2.6 (1.5–9.0)0.25

At hospital admission, the most common clinical signs were a decrease in appetite (n = 31 [62%] cats), vomiting (21 [42%]), polyuria or polydipsia (6 [12%]), and anuria (2 [4%]). Median serum urea and creatinine concentrations were 149 mg/dL (range 43 to 570 mg/dL; reference interval, 30 to 60 mg/dL) and 5.26 mg/dL (range, 1.3 to 19.3 mg/dL; reference interval, 0.6 to 1.5 mg/dL), respectively (Table 2). Median serum potassium concentration was 4.25 mEq/L (range, 3.2 to 8.1 mEq/L; reference interval, 3.5 to 5 mEq/L).

Table 2—

Median (range) serum urea and creatinine concentrations of the cats in Table 1 at various points before (at hospital admission) and after placement of DPU stents or UB devices.

 Urea* (mg/dL)Creatinine (mg/dL)
Measurement pointStent groupUB groupStent groupUB group
Admission130 (43–570)169 (83–337)5.0 (1.3–19.3)5.8 (1.8–13.7)
2 days after placement73 (30–190)82 (28–100)1.9 (0.6–6.3)2.0 (1.1–2.3)
1 mo after placement100 (50–149)80 (59–95)1.9 (1.3–3.8)2.0 (1.07–2.7)
3 mo after placement70 (32–120)70 (35–125)1.6 (1.1–2.8)1.9 (1.2–3.8)
6 mo after placement80 (50–130)60 (36–100)2.0 (1.4–2.7)2.0 (1.0–3.5)
1 y after placement70 (50–324)60 (32–120)1.7 (1.3–8.9)2.1 (1.3–4.8)

The reference interval for serum urea concentration was 30 to 60 mg/dL.

The reference interval for serum creatinine concentration was 0.6 to 1.5 mg/dL.

The number of cats included in data calculations decreased over time. Twenty-seven and 23 cats were included in the stent and UB groups, respectively, for serum urea and creatinine concentrations at admission, 26 and 23 cats 2 days after device placement, 21 and 20 cats 1 month after placement, 19 and 20 cats 3 months after placement, 19 and 18 cats 6 months after placement, and 15 and 18 cats 1 year after placement.

Prior to surgery, all cats had abdominal ultrasonographic evidence of ureteral obstruction, including hydronephrosis and hydroureter. Median renal pelvic diameter in the affected kidney was 11 mm (range, 1 to 40 mm), and median ipsilateral ureteral diameter was 3 mm (range, 1.5 to 9 mm; Table 1). Eight cats had nephrolithiasis. No significant differences in preoperative variables were identified between treatment groups.

Surgical treatment

Ten cats (3 in the stent group and 7 in the UB group) received bilateral surgical treatment during the study period. All others had 1 DPU stent or UB device placed unilaterally. Two cats in the stent group underwent emergency placement of a nephrostomy tube before surgery. Four cats in the UB group had undergone a previous surgery, including stent insertion (n = 3) and ureterotomy (1).

Median duration of surgery was significantly (P < 0.01) longer in the stent group (77 minutes; range, 44 to 160 minutes) than in the UB group (47 minutes; range, 35 to 85 minutes). Of the 30 ureteral stents placed, 21 (70%) were placed in an antegrade manner and 9 (30%) in a retrograde fashion when the antegrade attempt had failed. Median duration of hospitalization was also significantly (P < 0.001) longer in the stent group (7 days; range, 4 to 23 days) than in the UB group (4 days; range, 1 to 8 days).

Outcomes

Both types of devices provided an improvement in renal function over preoperative conditions, as indicated by a decrease in serum creatinine and urea concentrations by 48 hours after surgery (P < 0.001; Table 2). No significant difference in these concentrations was identified between groups.

The mortality rate in the stent group before hospital discharge was 19% (5/27), and that for the UB group was 13% (3/23). These rates did not differ significantly (P = 0.71). Five cats in the stent group died during hospitalization because of lack of renal function improvement (n = 4) and uroabdomen (1). Of these 5 cats, 1 died following cardiopulmonary arrest. Owners of the other 4 cats elected euthanasia. Three cats in the UB group were euthanized in the hospital because of lack of renal function improvement.

On hospital admission, median creatinine concentration in cats that died because of lack of improvement in renal function (9.5 mg/dL; range, 4.9 to 19.3 mg/dL) was significantly (P = 0.01) greater than in the cats that survived to hospital discharge (4.9 mg/dL; range, 1.3 to 13.7 mg/dL). Additional ultrasonographic findings in those cats included unilateral ureteral obstruction and severe changes secondary to chronic kidney disease, such as irregular renal contours, increased echogenicity of the renal cortex, and poor quality of corticomedullary differentiation.

Uroabdomen was identified only in cats in the stent group, and this was noticed between 2 hours and 10 days after surgery (n = 5). Of the 5 affected cats, 3 underwent a second laparotomy for revision surgery, which revealed leakage of urine at the ureterovesical junction (n = 2) or ureteral tear (1). Two of the 3 cats underwent neoureterocystostomy, and the other underwent nephrectomy. The remaining 2 cats with uroabdomen died because their owners elected euthanasia (owing to the poor prognosis for one cat and cardiopulmonary arrest on recovery for the other cat).

Twenty-two cats in the stent group and 20 cats in the UB group were discharged from hospital after surgery. Median postoperative duration of hospitalization was significantly (P = 0.002) shorter in the UB group (3 days; range, 1 to 6 days) than in the stent group (5 days; range, 2 to 16 days).

At long-term follow-up (median interval from surgery to follow-up, 19 months; range, 6 to 54 months), cats in the stent group were more likely to have recurrent signs of lower urinary tract disease, such as hematuria or pollakiuria and stranguria, than were cats in the UB group (Table 3). With regard to the severity of dysuria, no cat in the stent group and 5 cats in UB group reportedly urinated 1 to 2 times/d, 8 cats in the stent group and 10 cats in the UB group urinated 2 to 5 times/d, 8 cats in the stent group and 3 cats in the UB group urinated 5 to 10 times/d, and 6 cats in the stent group and 1 cat in the UB group urinated > 10 times/d. Cats treated with DPU stents were significantly (P = 0.005) more likely to have postoperative signs of dysuria than cats treated with a UB device. Only cats in the stent group had signs of flank pain (23% [5/22]). Long-term follow-up information obtained by telephone was available for 22 and 19 cats in the stent and UB groups, respectively.

Table 3—

Number (%) of cats in Table 1 with various short-term (1 week to 1 month after surgery) and long-term (> 1 month after surgery) complications.

Complication, by groupShort-termP valueLong-termP value
Dysorexia
  Stent group3 (11)0.616 (27)0.02
  UB group1 (4)0 (0)
Stranguria or pollakiuria
  Stent group1 (4)1.0012 (55)0.03
  UB group1 (4)4 (20)
Hematuria
  Stent group4 (15)0.3510 (45)0.047
  UB group1 (4)3 (15)
Occlusion
  Stent group0 (0)1.007 (32)0.047
  UB group0 (0)1 (5)
Signs of flank pain
  Stent group0 (0)1.005 (23)0.049
  UB group0 (0)0 (0)

— = Not applicable.

For short-term follow-up, the stent group included 27 cats and the UB group included 23 cats. For long-term follow-up, these numbers were 22 and 20, respectively.

Occlusion of the device was a common complication at long-term follow-up and was significantly more common in the stent group than in the UB group (Table 3). In the 7 cats with occlusion in the stent group, the stent system needed to be replaced a median of 12.8 months (range, 3 to 36 months) after surgery because of occlusion and encrustation (Figure 2).

Figure 2—
Figure 2—

Photographs of devices removed from cats with obstructive ureterolithiasis several months after placement because of obstruction and encrustation. A—Retrieved DPU stent with extensive mineralization This cat had a retained stent for months. An open surgical approach was required to exchange the stent. B—Retrieved UB device (nephrostomy catheter [asterisk] and cystotomy catheter [dagger]) with mineralization after 14 months of placement. Laparotomy was performed to exchange the UB device.

Citation: Journal of the American Veterinary Medical Association 251, 4; 10.2460/javma.251.4.429

The percentage of cats requiring additional surgical procedures was significantly (P = 0.01) greater in the stent group than in the UB group. Twelve (44%) cats in the stent group required additional procedures because of stent occlusion (n = 7), uroabdomen (3), and severe and refractory signs of cystitis (2). The 2 cats with severe cystitis underwent replacement of the stent with a UB device, and dysuria resolved after the procedure. Two (9%) cats in the UB group had additional surgical procedures because of UB occlusion (1 cat at 14 months after device placement; Figure 2) and lower urinary tract obstruction (1 cat at 3 months after device placement).

Cats in the stent group had a significantly (P = 0.04) shorter median survival time (14 months) than cats in the UB group (not enough cats died in this group to support calculation of median survival time; Figure 3). Results of Kaplan-Meier analysis indicated that by 3 months after surgery, only 70% of cats in the stent group were still alive, whereas this was the survival rate at 14 months for cats in the UB group. Eight (30%) cats in the stent group and 16 (70%) cats in the UB were still alive at the end of the study; the remaining 19 cats in the stent group and 7 cats in the UB group died or were euthanized for reasons generally related to urinary tract problems. No cat was lost to follow-up. Fourteen (52%) cats died or were euthanized after hospital discharge in the stent group (9 died of progression of chronic kidney disease, 3 of stent occlusion, 1 of hyperthyroidism, and 1 of pericardial effusion). Four (17%) cats in the UB group died or were euthanized after discharge (1 of severe multidrugresistant bacterial pyelonephritis, 1 of pericardial effusion, 1 of refractory seizure, and 1 of device occlusion).

Figure 3—
Figure 3—

Kaplan-Meier survival curves for cats with obstructive ureterolithiasis that underwent surgical placement of a DPU stent (n = 27; solid line) or UB device (23; dashed line). Cats in the stent group had a significantly (P = 0.04) shorter survival time than cats in the UB group. Hash marks indicate censored cats.

Citation: Journal of the American Veterinary Medical Association 251, 4; 10.2460/javma.251.4.429

Discussion

Ureteral stents and UBs have been developed to overcome the limitations of traditional techniques for the treatment of ureteral obstruction in cats. Comparisons of clinical outcomes after placement of ureteral stents and UB devices for the treatment of ureterolithiasis in cats were previously lacking in the veterinary literature. The main findings of the present study were a shorter duration of surgery, fewer complications, fewer additional procedures after device placement, and longer survival time in cats that received a UB device rather than a DPU stent at our facility. Cats undergoing placement of a DPU stent or UB device had predischarge mortality rates (up to 18% and 13%, respectively) that were similar to previously reported mortality rates of 8% to 16%.13–16 The main cause of death during hospitalization in both groups was lack of an improvement in renal function.

Cats with ureteral obstruction are at risk of progressing to end-stage chronic kidney disease because of the loss of a large proportion of their nephrons by the time veterinary care is sought. In a previous study17 involving dogs, the glomerular filtration rate was permanently diminished by a mean of 35% after 7 days of obstruction.17 Therefore, the prognosis for cats with ureteral obstruction remains uncertain, primarily because of chronic kidney disease. Decreasing the duration of general anesthesia during obstruction-relieving surgery could reduce additional damage to the remaining nephrons.14 However, the benefit to renal function of the briefer anesthetic session required for the placement of a UB device versus a DPU stent was not established in the present study, possibly because this benefit may be marginal in highly damaged kidneys. The longer anesthetic episode for cats that received the DPU stent probably reflected the more challenging nature of the procedure, which is more invasive and requires a longer surgical period and more extensive surgical training. Indeed, only board-certified surgeons (CP and GR) placed the DPU stents in the present study, in contrast to UB devices, which were placed by a supervised third-year surgery resident.

The most common perioperative complication in the stent group was development of uroabdomen (18% of cats), which is consistent with other reported findings.14 No urinary leakage was observed with the UB device in the present study, whereas in another study,13 6 of 14 cats had leakage. A new locking-loop nephrostomy catheter has been developed to decrease the risk of nephrostomy catheter migration and potential leakage.13

The most common postoperative complication in the stent group was recurrent lower urinary tract signs; 48% of cats had stranguria or pollakiuria, and 52% had hematuria. Dysuria reportedly develops in up to 40% of cats or dogs after ureteral stent placement.5,14,16 In human medicine, ureteral stents are also commonly associated with adverse effects, such as irritating voiding symptoms (eg, increased urinary frequency), flank pain, suprapubic pain, and hematuria, in 40% to 95% of patients.8,9,18 In the present study, signs of flank pain were detected in 23% of cats in the stent group. To our knowledge, this complication of ureteral stent placement is well documented for humans but has not previously been reported for cats or dogs.7 Flank pain is most likely the result of urine reflux toward the kidney, leading to an excessive increase in intrapelvic pressure and subsequent pain.19

Cats developed signs of cystitis significantly more commonly with DPU stents than with UB devices (52% in stent group and 22% in UB group). Furthermore, 2 cats in the stent group with refractory signs of cystitis required replacement of the stent by a UB and had immediate resolution of the dysuria.

The exact cause of the signs of lower urinary tract disease in cats in the stent group remains unclear. One possible explanation is irritation of the urinary bladder urothelium by the distal stent curl (rather than the bladder catheter of the UB system) owing to differences in the lengths of the indwelling portion within the urinary bladder. The mechanical hardness and position of the curl of the DPU stent inside the urinary bladder could also have contributed, given that the curl is positioned at the dorsolateral surface of the urinary bladder just cranial to the bladder neck and on the trigonal region, and the UB device is positioned at the apex of the urinary bladder.

In humans, symptoms of lower urinary tract disease are associated with incorrect length or position of the stent.12,20 Results of 1 study21 involving humans suggested that urinary stent–related symptoms may be attenuated by intravesical submucosal injection of ropivacaine. Furthermore, a soft-tail stent is reportedly less irritating to the urinary bladder than a conventional DPU stent.22 Nevertheless, no associations were identified in a study16 between cats that received soft stents and cats that received stiff stents and between the lengths of the portion of the 2 types of stents implanted within the urinary bladder.

At long-term follow-up in the present study, cats in the stent group were significantly more likely to have device obstruction because of encrustation (26%) than cats in the UB group (4%), which is consistent with findings in another study,16 in which reobstruction of the ureter occurred in up to 20% of cats. In humans, stent encrustation represents a serious complication, developing within 6 weeks after surgery in 26.8% of patients.11 Encrustation can obstruct the device, impair urinary flow, and adversely affect renal integrity.11,23 Although the exact mechanism of stent encrustation in sterile urine is unclear, it appears to be dependent on urinary pH, and the presence of uroliths is the major risk factor.24 Other common risk factors for stent encrustation in humans that may also apply to cats include a prolonged implantation period, urinary infection, chronic kidney disease, and properties of the biomaterial used.25–27

In the present study, the DPU stents and UB devices were composed of the same biomaterial (polyurethane) and the same radio-opacifying substance was used (barium). Polyurethane is one of the most biocompatible materials used in the manufacture of various medical devices. Addition of barium sulfate is known to have a negative influence on the smoothness and lubricity of the inner and outer surfaces of polyurethane catheters. The sulfate anion is displaced from the insoluble barium sulfate by the high chloride anion concentration in urine, leading to the formation of water-soluble barium chloride, which is a highly toxic compound capable of inducing encrustation.28 Because indwelling time has been established as an important factor in the development of encrustation, recommendations in human medicine are that, to avoid encrustation, stents should be maintained in situ between 2 and 6 months and then removed before resorting to a permanent treatment for ureterolithiasis.7–11 In comparison, ureteral devices in cats are kept in place as long as possible because permanent surgical removal of urolith is not performed.

Indwelling ureteral stents and UB devices appear to be tolerated longer in cats than in humans. In the present study, the lower percentage of cats with device encrustation in the UB versus stent group could have been attributable to a larger cross-section of the UB device or the mechanical effect of flushing, which was performed every 3 to 4 months under ultrasonographic guidance. The need for a second surgery because of device encrustation was significantly greater in the stent group than in the UB group. Similar data were obtained in another study,16 in which stent exchange was necessary in 19 (27%) cats owing to device reobstruction. The median interval from original stent placement to stent exchange was 67.5 days in that study,16 which is much shorter than the median of 12.8 months in the present study, probably because that study included cases of stent migration (which occurred in 4 of 79 [5%] stented ureters in 69 cats).16

The major limitation of the present study was its retrospective nature. No random selection of patients was performed; rather, cats in each group were selected from nonparallel periods in the medical records, which was necessary because UB devices and, hence, cats that received it were not available until 2013. However, we addressed this issue by demonstrating nondiscrepant baseline data and comparable follow-up durations for the 2 treatment groups. Although the cohorts of cats in the present study represent the largest regarding treatment of ureterolithiasis in the literature, the number of subjects per group was low.

One objective of the present study was to compare outcomes and complication rates in cats undergoing placement of DPU stents or UB devices. Ureteral stents and UB devices are useful to relieve ureteral obstruction. The prognosis of cats with urolithiasis treated with DPU stents or UB devices remains guarded, primarily because urolithiasis contributes to the progression of chronic kidney disease, but also because of long-term complications (eg, dysuria or device occlusion). Although ureteral stents have established benefits in the treatment of ureteral obstruction, the UB device appeared superior to the DPU stent in outcomes and complication rates in this retrospective study.

Acknowledgments

No financial support was received for this study. The authors declare that there were no conflicts of interest.

Presented as an abstract at the Annual Scientific Meeting of the European College of Veterinary Surgeons, Lisbon, July 2016; and the 2016 American College of Veterinary Surgeons Surgery Summit, Seattle, October 2016.

The authors thank Drs. Eymeric Gomez, Emilie Fauchon, Camille Bismuth, Rosario Vallefuoco, Rodolpho Oliveira, Marie Vagney, and Florence Mugneret for technical and clinical assistance.

ABBREVIATIONS

DPU

Double-pigtail ureteral

UB

Ureteral bypass

Footnotes

a.

CDM Lavoisier, Paris, France.

b.

Valium, Roche, Saint Priest, France.

c.

Propolipid 1%, Fresenius Kabi, Schelle, Belgium.

d.

VetFlurane, Virbac, Carros, France.

e.

2.5F Vet Stent-Ureter, Infinity Medical LLC, Menlo Park, Calif.

f.

SUB, Norfolk Vet Products, Skokie, Ill.

g.

Norfolk Vet Products, Skokie, Ill.

h.

Omnipaque (350 mg of iodine/mL), GE Healthcare, Limones, France.

i.

Hill's c/d, Hill's Pet Nutrition Inc, Valbonne, France.

j.

Vetergesic, CEVA Sante Animale, Libourne, France.

k.

XLSTAT Biomed, version 2015.5, Addinsoft, New York, NY.

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