Ultrasound-guided percutaneous antegrade hydropropulsion to relieve ureteral obstruction in a pet guinea pig (Cavia porcellus)

Abstract

Severe hydroureter and hydronephrosis secondary to ureteral obstruction by calculus were present in a guinea pig. A palliative ultrasound-guided percutaneous antegrade hydropropulsion was performed under general anesthesia to relieve the ureteral obstruction and the associated clinical signs. We describe the technique and the considerations for its potential application in similar cases.

Urolithiasis is a common disease in guinea pigs (Cavia porcellus)(1–3). Clinical signs associated with the disease vary with the size and location of the calculi along the urinary tract (1). Imaging used for the diagnosis of the urinary calculi commonly include survey radiographs, abdominal ultrasonography and more rarely, excretory intravenous urography and computed tomography (CT) (1). Supportive and symptomatic treatment should be provided (4). Surgical removal of the urinary calculi is considered the treatment of choice (5–7) as medical treatment of urolithiasis is ineffective in guinea pigs (1). Specifically, surgery is considered the preferred procedure for relief of ureteral obstructions (1,6,7).

This report describes the palliative clinical management of a complicated ureteral obstruction using an ultrasound-guided percutaneous antegrade nephrocentesis and hydropropulsion in a guinea pig. The potential advantages and disadvantages of using this technique in the management of this condition are discussed.

Case description

A 2-year-old neutered male Peruvian guinea pig (Cavia porcellus) was referred to the Avian and Exotic Service of the Ontario Veterinary College Health Sciences Centre, University of Guelph after showing non-specific clinical signs of illness. The guinea pig was housed with another neutered male guinea pig that was apparently healthy. Both animals were kept in a 1.0 m × 1.5 m cage with recycled paper bedding. The diet consisted of free choice hay, commercial guinea pig pellets, and a variety of vitamin C-containing vegetables and fruits. Water was provided via a sipper bottle. One month prior to the presentation the owners noticed that the guinea pig was becoming increasingly quiet, partially anorexic, and was losing weight. Hematuria was observed by the referring veterinarian who suspected a urinary tract infection. Abdominal radiographs were unremarkable at that time. The guinea pig was treated with a 2-week course of trimethoprim-sulfa (TMS) and showed some clinical improvement with general recovery and cleared urine. However, the initial clinical signs recurred shortly after the treatment ended. The guinea pig was referred for further evaluation.

On presentation, the guinea pig was thin (body condition score of 1.5/5) and weighed 613 g. Pain was elicited on abdominal palpation and the guinea pig vocalized and tensed when the abdomen was touched. Red-pigmented urine was collected by free-catch and hematuria was confirmed using both the urine dipstick (Multistix 10 SG reagent strips; Bayer Corporation, Elkhart, Illinois, USA) and urine cytology.

A blood sample was collected from the right jugular vein, placed in heparin-coated tubes and submitted for complete blood (cell) count (CBC) and blood biochemistry profile. Blood test results were compared to in-house laboratory reference intervals and were unremarkable apart from a mild-low hematocrit (30 L/L; reference interval: 39 to 55) that was attributed to the chronic hematuria.

Differential diagnoses for the hematuria included urolithiasis, urinary tract infection, and neoplasia.

The guinea pig was sedated using butorphanol (Pfizer Canada, Kirkland, Quebec), 0.5 mg/kg body weight (BW), IM, and midazolam (Sandoz Canada, Boucherville, Quebec), 0.5 mg/kg BW, IM. Once sedated, the guinea pig was placed in dorsal recumbency and the ventral abdominal hair was clipped from the sternum to the inguinal area. Ultrasound examination was performed with a standard ultrasound device (Philips iU22; Philips Medical Systems, Bothell, Washington, USA), using an 8.5-MHz probe. The abdomen was scanned and showed no abnormalities apart from those related to the urinary system. A 2.3-mm nephrolith was observed in the pelvis of the right kidney. A 4-mm ureteral stone was also observed at the left ureteral papilla (Figure 1), with dilatation of the left ureter and left renal pelvis. Doppler color flow was used to differentiate the dilated ureter from abdominal blood vessels. The final diagnosis was ureteral calculi obstruction causing a unilateral hydroureter and hydronephrosis, and a nephrolith in the contralateral kidney.

Figure 1.

Transverse ultrasound image from the guinea pig with ureteral obstruction. Note the urinary bladder and a region of hyperechoic mineral at the level of the left ureter.

Treatment options were considered and included laparotomy with ureterotomy to remove the stone and medical management of the clinical signs associated with the condition. Since the owners declined performing surgery to remove the obstructing calculus, a palliative nephrocentesis was performed with the goals of relieving pressure on the kidney and hydropropulsion to attempt relieving the obstruction by advancing the calculus into the bladder.

For the procedure, the guinea pig was completely immobilized using general anesthesia. While still under the previous sedation, he was mask-induced with 8% sevoflurane (Sevoflurane; Abbott Laboratories, St. Laurent, Quebec) in oxygen with a flow rate of 2 L/min delivered via a tight-fitting anesthetic face mask and maintained at 3% for the duration of the procedure. Vital signs were monitored by direct visualization, stethoscope, and pulse oximetry (Nonin PalmSat 2500; Minneapolis, Minnesota, USA).

The procedure was performed under sterile conditions. Ultrasound-guided pyelocentesis was performed with a 22-gauge Teflon-coated intravenous catheter (BD Insyte-W; Becton Dickinson Infusion Therapy System, Sandy, Utah, USA) inserted percutaneously (Figure 2). A short infusion extension line and a 3-way stopcock were connected to the needle. A 5-mL syringe was attached and the urine was aspirated by applying gentle negative pressure. The urine was placed into sterile collecting tubes and saved for further evaluation. Hydropropulsion with sterile saline was applied via a new infusion line connected to a 5-mL syringe. Several attempts using gentle pressure were made under concurrent ultrasound examination. The hydro-propulsion managed to partially relieve the obstruction as urine and fine hyperechoic particles were observed to freely flow from the previously blocked ureter into the bladder (Figure 3). Hydropropulsion attempts were made to dislodge the ureteral stone into the bladder. However, the ureteral stone was only partially movable and after about 15 mL of total infused fluids, the procedure was aborted. The guinea pig recovered uneventfully from the procedure and was sent home the same day with home care instructions, including trimethoprim-sulfamethoxazole (Teva Pharmaceuticals; Sellersville, Pennsylvania, USA), 30 mg/kg BW, PO, q12h, meloxicam (Metacam 1.5 mg/mL oral suspension; Boehringer Ingelheim Vetmedica, Burlington, Ontario) 0.3 mg/kg BW, PO, q12h, and assisted feeding (Critical Care for Herbivores; Oxbow Pet Products, Murdock, New England, USA), 15 to 20 mL, PO, q4 to 6 h.

Figure 2.

Ultrasound-guided pyelocentesis was performed with a 22-gauge Teflon-coated intravenous catheter (BD Insyte-W, Becton Dickinson Infusion Therapy System Inc., Sandy, Utah, USA) percutaneously inserted into the renal pelvis.

Figure 3.

Real-time ultrasound image demonstrating hyperechoic sediment that was flushed into the urinary bladder and formed a focal burst centered on the left ureteral papilla.

The guinea pig was scheduled for a recheck within 1 wk for repeated CBC and biochemistry tests, urinalysis, and abdominal ultrasound and with a standing recommendation for surgical removal of the ureteral stone. However this case was lost for physical follow-up. The owners reported that the guinea pig had regained its normal habits within 1 d, did not require the assisted feeding, and did not show any evidence of hematuria. The meloxicam and the antibiotics were discontinued within 1 and 2 wk, respectively. The guinea pig continued to do well at home with no visible clinical signs noticed by the owners and was lost for follow-up 7 mo after his initial presentation.

Discussion

Urolithiasis is a common disease in guinea pigs and is more prevalent in animals over 2 years of age in both males and females (1–3). Stone composition can be either calcium oxalate (8,9) or calcium carbonate (4). Urinary tract infection was associated with some of the cases and various bacterial species were cultured from urine or the calculi (4,8). This guinea pig was of a Peruvian breed which is considered (but never confirmed) to have a predisposition to develop urolithiasis (4). Risk factors contributing to urolithiasis include inadequate water intake, urine retention, inadequate cage hygiene, obesity, lack of exercise, food items with high mineral content, renal disease, and vitamin or mineral supplementation (5). Clinical signs associated with the disease vary with the size and location of the calculi along the urinary tract (1,10,11). Stones located higher in the urinary tract can cause lethargy, anorexia, weight loss and pain (1,10,11), similar to what was observed in this case.

The patient’s history, clinical signs, and physical examination findings may suggest the disease (1). Clinical pathology, including a CBC, a blood biochemistry panel, and urinalysis can aid in determining the overall health status of the patient. Specific diagnosis of urinary calculi requires imaging studies, including survey radiographs, abdominal ultrasonography, excretory intravenous urography and CT (1,10,11). Survey radiographs performed by the referring veterinarian did not show the ureterolith in this guinea pig. Although radio-opaque, urinary calculi can be misidentified on survey radiography, depending on their size, number, and location (1). In cats, radiography alone was 60% sensitive and 100% specific for detecting nephroliths or ureteroliths (5). Abdominal ultrasonography is useful for specific determination of urinary calculi location, number and associated problems such as hydronephrosis or hydroureter, urinary leakage, mucosal changes (1), and other (non-urinary tract) abdominal pathologies (7,10,11). Ultrasound-guided cystocentesis is useful for collecting a sterile urine sample for bacterial assays and general urinalysis (1).

Supportive and symptomatic treatment should be provided, including hydration, analgesia, anti-inflammatories, assisted feeding, and antibacterial treatment when indicated (4). Medical treatment of urolithiasis has been unrewarding in guinea pigs (1). Surgical removal of the urinary calculi is the treatment of choice (5–7). The removed stone should be submitted for mineral analysis and bacterial assays together with urinary tract mucosa biopsy (5,6). Recurrence of the condition is common and owners should be advised accordingly (5,6).

Two cases of hydronephrosis and hydroureter due to ureterolith obstruction were previously described in guinea pigs (10,11), and one of them was associated with a papilloma formation in the affected ureter (11). In cats and dogs, most ureteroliths are composed of calcium oxalate (98% and 50%, respectively) (7).

The immediate goal for any ureteral obstruction should be early relief of the obstructed ureter (7). In dogs, glomerular filtration rate (GFR) was permanently decreased after 7 and 14 days of obstruction by 35% and 54%, respectively (7).

In cats and dogs, therapy for obstructive ureteral disease includes medical management, surgery, and interventional therapy (stent placement) (7). Non-invasive medical management, including aggressive fluid therapy and diuretics, may first be attempted with a goal of forcing the passage of the ureterolith. However, it has been reported to be effective in just 10% of cats (7). Surgery is the preferred procedure for relief of ureteral obstructions (1,6,7). In guinea pigs, a ureterotomy procedure has been described (6,10,11). Surgery has the advantage of direct visualization of the abnormality, allowing for physical removal of the obstruction. However, significant complications following the procedure, including leakage and ureteral stricture, were reported in dogs and cats (6). Similar complications may be expected in guinea pigs, especially given the challenges of their relatively smaller size. Given these risks, many cases presented with partial obstruction are often left untreated (7). In cats and dogs, ureterotomy can be avoided with placement of ureteral stents, thus allowing for bypass of the obstructed section of the ureter (7).

The procedure described in this case report is very similar to what is described for percutaneous antegrade pyelography in dogs and cats, in which a 22-G IV catheter is aseptically placed through the greater curvature and into the renal pelvis of chemically immobilized patients (7). In this technique, urine samples can be sterilely collected for urinalysis and bacterial culture (7). This is typically performed using positive contrast and concurrent fluoroscopic evaluation to determine ureteral patency. The modification of the technique, performed herein is that sterile saline was injected instead of a contrast agent because the goal was to flush the ureteral stone, not to image the ureter itself. This allowed for partial opening of the obstruction by flushing the smaller sediment and calculi from around the larger calculus and allowed urine to flow from the kidney and into the bladder, thus resolving some of the clinical signs. Complications described with antegrade pyelography include hemorrhage and peritoneal leakage of contrast material (12). Minimal peritoneal fluid was observed following the procedure in the current case, consistent with peritoneal leakage of contrast that was reported in 8/18 cats undergoing antegrade diagnostic pyelography (12).

In conclusion, although antegrade hydropropulsion did not completely clear the obstruction in this guinea pig, it did allow for clinical resolution of the associated clinical signs. This technique can be considered in cases in which complete ureteral obstruction was diagnosed and immediate intervention is indicated to relieve the urine pressure within the kidney. Where surgery cannot be performed, due to the overall health status of the patient or the owners’ consideration of the risk and benefit, partial relief of the obstruction using percutaneous hydropropulsion can also be considered. CVJ