Introduction

Urethral catheterization is a common procedure for diagnosis, treatment, or monitoring purposes, particularly in patients with critical illness. Indwelling catheterization is often used for continuous urine collection in patients with critical illness or immobility, for the treatment of acute urinary obstruction or urine retention, for postoperative urinary diversion, and for urine output monitoring. Intermittent catheterization is performed for radiographic contrast procedures, to relieve urinary obstruction, and for urine sampling.^1,2

The standard approach typically involves using a balloon-tipped Foley catheter or a general-use catheter, such as a red rubber catheter. In some pediatric cases, alternative tubing materials, including feeding tubes, have been commonly used. However, feeding tubes are not designed for urethral catheterization, and their off-label use in this context is unconventional and potentially problematic.³

Unlike standard urinary catheters, feeding tubes lack essential structural and functional features necessary for safe and effective urethral catheterization, such as a balloon for retention and appropriate flexibility to minimize trauma. In veterinary medicine, the use of feeding tubes as urethral catheters has been anecdotally mentioned in a textbook, and a study of feline urethral obstruction has documented its application.^4,5 However, there has been no systematic research evaluating their safety, usage considerations, or potential complications. Although feeding tubes have been used as alternative urethral catheters in certain situations, their off-label application lacks scientific validation.

This report describes two cases in which nasogastric feeding tubes, used as urethral catheters, became entrapped within the urethra, necessitating a novel nonsurgical approach for removal. These cases highlight the risks associated with using nonstandard materials for urethral catheterization and propose a minimally invasive technique to manage complications.

Case Reports

Case 1

A 13 yr old castrated male Pomeranian weighing 4.5 kg was presented with polyuria/polydipsia and urinary bladder calculi. On physical examination, the body temperature was 39°C, heart rate was 150 beats per minute, and the respiratory rate exceeded 60 breaths per minute. During auscultation, a grade 4/6 heart murmur was detected. Oscillometric arterial blood pressure was 114/94 (mean arterial pressure of 100) mm Hg. Thoracic radiography revealed cardiomegaly (vertebral heart scale, 12.0; normal range, 8.7–10.7⁶) and left atrial enlargement (vertebral left atrial size, 2.7; normal range, 1.4–2.2⁷). Complete blood count revealed no abnormalities, and serum chemistry showed elevated alkaline phosphatase (433 U/L; reference range, 47–254 U/L, as provided by the manufacturer^a). A cystocentesis was planned; however, because of insufficient urine volume on ultrasonography, urethral catheterization was attempted using a 6-Fr, 50-cm-long nasogastric feeding tube^b made of polyvinyl chloride. After obtaining a urine sample through the nasogastric feeding tube, the attempt to remove the tube was unsuccessful. After several unsuccessful attempts, the patient was transferred to the department of surgery with the initial intent to surgically remove the lodged tube.

Before undertaking surgery, a radiographic examination of the abdominal region revealed that the nasogastric feeding tube was lodged in the membranous urethra near the ischial arch (Figure 1A). In addition, cystic calculi were identified in the bladder. To alleviate pain associated with attempts to withdraw the catheter, IV butorphanol (0.3 mg/kg) was administered as premedication, followed by a slow titration of IV propofol to induce deep sedation. During the sedation procedure, the flow-by method was employed to administer oxygen (4 L/min) to the dog. Under deep sedation, with the dog in the right lateral recumbence, a 22-gauge over-the-needle IV catheter^c without the stylet needle was inserted alongside the original tube through the dog’s urethral orifice. Then, a 20 mL syringe filled with sterile saline was attached to the inserted catheter. The procedure involved applying digital pressure to the external urethral orifice by the surgeon, while the assistant simultaneously compressed the pelvic urethra by inserting a finger into the rectum and pressing it against the dorsal surface of the pelvic bones. As this pressure was applied, sterile saline was flushed into the over-the-needle catheter, effectively expanding the urethra (Figure 1B). Careful and gentle traction was applied to the lodged tube, and the feeding tube was withdrawn smoothly.

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The patient recovered from sedation event-free and was discharged that day. No significant findings in the urine culture test results were noted, and during the follow-up the next day, no side effects such as hematuria or difficulty in urination were observed. The cystic calculi in the bladder were not surgically treated at our institution. Instead, it was decided to monitor and plan treatment at a primary veterinary hospital in the future.

Case 2

An 11 yr old castrated male Maltese weighing 4.7 kg was referred for further diagnostic examinations for hyperadrenocorticism. The dog had a history of tachycardia, hypertension, and panting. On physical examination, the body temperature was 38.9°C, heart rate was 212 beats per minute, and the respiratory rate exceeded 60 breaths per minute. The noninvasive systolic arterial blood pressure measured by the Doppler ultrasonic device was 170 mm Hg. The mucous membranes were pink, and the capillary refill time was <1.5 s. Bilateral submandibular, prescapular, and popliteal lymph nodes were palpable. Complete blood count revealed no abnormalities, and serum chemistry showed elevated alkaline phosphatase (1557 U/L; reference range, 47–254 U/L, as provided by the manufacturer^a).

To acquire a urine sample for further examination, urethral catheterization was attempted using a 6-Fr, 50-cm-long nasogastric feeding tube^b, which was inserted into the urethra and advanced into the bladder. Placement of the urethral catheter was confirmed via lateral abdominal radiography, but the tube appeared to be overly inserted in the bladder (Figure 2A). The urine sample was clear yellow. The urine specific gravity was 1.028, and microscopic examination revealed nonspecific findings. The sample was also used for the urine creatinine-cortisol ratio test, and the result was 16.2 nmol/mmol (cut-off value, 16.1 nmol/mmol⁸), indicating a mild elevation consistent with possible hyperadrenocorticism. After urine sampling, a resistance was noted on the attempted removal of the tube, and the patient reacted painfully to repeated removal attempts. Forward advancement toward the urinary bladder was also not possible. On lateral abdominal radiography, the urethral catheter was observed to be bent on itself, with its tip positioned distal to the base of the os penis (Figure 2B).

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Before further attempts to remove the kinked tube, the dog was premedicated with butorphanol (0.3 mg/kg IV), and deep sedation was induced with propofol (total 3.5 mL IV, titrated to effect). During sedation, the flow-by method was used to deliver oxygen (4 L/min). In the first attempt to remove the spontaneously kinked tube, the infused sterile saline did not dilate the urethra and simply flowed back out from the tube. Before the dog was moved on to the surgical procedure, a final attempt was made to retract the kinked tube nonsurgically. Under deep sedation, the dog was placed in right lateral recumbence, and a 20-gauge over-the-needle IV catheter^c without the stylet needle was inserted alongside the original tube through the dog’s urethral orifice. Then, a 20 mL syringe filled with sterile saline was attached to the inserted over-the-needle catheter. Subsequently, following the same approach as in case 1, digital pressure was applied to the external urethral orifice and pelvic urethra through the rectum simultaneously followed by injecting sterile saline into the over-the-needle catheter. Gentle traction was applied, and the kinked feeding tube was smoothly withdrawn without complication.

The recovery from sedation was event-free, and the dog was discharged from the hospital that day. Three days later, the dog did not show any urinary-related side effects, including difficult urination and hematuria. During the telephone follow-up conducted 6 mo later, it was confirmed that there were no long-term urological complications that had developed.

Discussion

In these two cases, urethral catheterization was performed using a 6-Fr, 50-cm-long nasogastric feeding tube. According to veterinary literature, Foley catheters or red rubber catheters are generally recommended for urethral catheterization.^2,4 However, in certain instances where urine collection is not performed via cystocentesis, some veterinarians routinely use nasogastric feeding tubes for urine sampling. This practice may stem from the frequent use of nasogastric feeding tubes for enteral nutrition in the authors’ animal hospital, which may have inadvertently led to their inappropriate application for urine collection. These factors may have contributed to the catheter entrapment and kinking observed in the present cases, highlighting the potential complications associated with the inappropriate use of nasogastric feeding tubes for urinary catheterization.

In pediatric medicine, enteral feeding tubes are sometimes used as temporary urinary catheters; however, their off-label use has been reported to cause complications, such as knot formation.³ In veterinary medicine, feeding tubes have been used as urethral catheters in feline patients, particularly in cases of urethral obstruction. One study reported that polyvinyl chloride infant feeding tubes were selected as urinary catheters in cats because of their radiopacity, flexibility, and length markings.⁵ However, there have been no prior reports of feeding tubes being used as urethral catheters in dogs, making this the first documented case of urethral catheter entrapment and kinking associated with their use. Given the anatomical differences between dogs and cats, further research is needed to determine whether feeding tube use in canine urethral catheterization may carry a higher risk of complications compared with feline patients.

The diagnosis of a kinked or entrapped urethral catheter should be suspected when catheter removal is unsuccessful or particularly difficult.⁹ Radiographic or ultrasonographic examination of the abdominal and perineal areas can confirm the diagnosis.^10,11 Radiographic indicators of catheter kinking include distortion of the round catheter lumen when viewed end-on, with straight-line or angular appearances at points of directional change, triangular configurations at bending points, bulging of the catheter material, and catheter buckling at sites of directional changes.¹² In the cases reported here, catheter malfunction was suspected owing to failed retraction attempts, and in case 2, complete kinking of the catheter was confirmed through radiographic examination. Furthermore, saline injected into the catheter was unable to pass through the urethra, suggesting complete obstruction at the kinked segment.

Urethral catheter kinking represents a rare but clinically significant complication in both human and small animal medicine.^9,10,12 Before the case series reported in 2011, only one canine case had been documented, published in 1967.¹⁰ Of the four cases described in the 2011 series, three involved urethral catheter kinking, whereas the remaining case was associated with urethral catheter knotting.⁹ Known risk factors for spontaneous catheter kinking include forceful insertion of the catheter through the urethra at the ischial arch and urethroliths obstructing the urethral passage.^9,10 Additionally, excessive insertion of the catheter into the bladder and bladder overdistension have been suggested as contributing factors in the development of loop formation and subsequent kinking.¹³ In case 2, excessive insertion of the catheter into a distended bladder was noted on lateral abdominal radiographs obtained after placement. In the radiograph (Figure 2A), the tip of the nasogastric feeding tube, which had been overinserted into the bladder, appeared bent in the opposite direction of its insertion. This suggests that retracting the tube may have caused the kinked segment to re-enter the urethra, leading to subsequent kinking. Unlike a Foley catheter, a nasogastric feeding tube lacks a retention mechanism, such as a balloon, which helps prevent excessive advancement. When a Foley catheter’s balloon is inflated with saline or sterile water, it remains anchored at the bladder outlet, minimizing the risk of overinsertion. In case 2, the use of a nasogastric feeding tube for intermittent catheterization resulted in kinking, likely because of overinsertion. These findings suggest that polyvinyl chloride feeding tubes may pose a higher risk of entrapment and kinking compared with standard urinary catheters.

In this report, a novel nonsurgical approach was successfully used to remove the kinked and entrapped catheter. When fluid injection through the original catheter was not possible, an over-the-needle catheter was placed alongside it to allow saline infusion and facilitate urethral dilation. This technique is similar to retrograde urohydropropulsion, a standard technique for removing urethral calculi in dogs.¹⁴ By blocking the urethral exit and applying rectal compression to the pelvic urethra, sufficient urethral dilation was achieved through rapid saline infusion, enabling successful catheter removal. In human medicine, several nonsurgical techniques have been described for retrieving knotted urethral catheters, including sustained retraction under general anesthesia, unraveling the knot using a guidewire, and endoscope-assisted retrieval.^3,15,16 If nonsurgical removal fails, surgical interventions such as urethrotomy and cystotomy may be required.^9,17 Similar approaches may be considered for kinked or entrapped urethral catheters in veterinary patients. If a kinked catheter can be advanced into the bladder, endoscopic or guidewire-assisted untangling or open cystotomy may be viable options. However, if catheter kinking occurs in the penile urethra, particularly at the os penis, where the urethral diameter is narrowest, retrograde advancement into the bladder may not be possible.¹⁸ In such cases, the nonsurgical approach introduced in this report, involving sustained retraction through urethral dilation, may be the only viable option before considering surgical extraction.

Despite the success of this method, several limitations should be considered. This technique is effective only for penile urethral dilation and may not be suitable if the catheter is lodged in the bladder or a more proximal segment of the urethra. Additionally, the procedure requires deep sedation or general anesthesia, which carries inherent risks. Furthermore, excessive force during catheter removal may damage the urethral mucosa, potentially leading to complications such as urethral trauma or stricture formation.

All reported cases of dogs with urethral catheter kinking were sexually intact males.^5,9 This case report describes the first reported case of urethral catheter kinking or entrapment in two castrated male dogs. Collagen content increases and the proportion of muscle decreases in the lower urinary tract of male dogs after gonadectomy, which may cause urethral stiffness and adversely affect the distensibility of the urethra.¹⁹ However, another study did not identify any differences in the maximum distension of the male urethra between intact and castrated male dogs.¹⁸ As this report only includes two cases, whether gonadectomy status affects urethral catheter kinking in the male dogs remains unclear. More studies are needed to determine whether neutering male dogs affects the occurrence of urethral catheter malfunction.

This case report highlights the potential complications of using feeding tubes for urethral catheterization and presents a novel method for the removal of entrapped catheters. However, preventing catheter kinking in the first place requires further consideration. One preventive measure might be to choose a catheter that is stiff enough to resist bending during advancement but not so stiff that it kinks. The catheter in the present report (made of polyvinyl chloride) and the three different types of tubes that kinked in a previous veterinary report⁹ (polyethylene urethral catheter, polyvinyl chloride indwelling tube, and polyvinyl chloride flexible red catheter) do not appear to meet these criteria. Although feeding tubes are not intended for urinary catheterization, their occasional use in veterinary medicine indicates the need for further evaluation of catheter material selection and insertion techniques. Investigating predisposing factors for catheter kinking and entrapment is valuable in developing guidelines to minimize these complications.³

Conclusion

Feeding tubes lack structural features suitable for urinary catheterization, and their flexibility and length may increase the risk of overinsertion, kinking, or entrapment. Urethral catheter kinking is a rare complication in small animal practice, and nonsurgical treatment options remain limited. In this report, two cases of urethral catheter kinking and entrapment in castrated male dogs were successfully managed using a modified retrograde urohydropropulsion technique, in which an over-the-needle catheter was inserted alongside the lodged catheter to facilitate urethral dilation and removal. Although this method requires deep sedation or general anesthesia, it may serve as a viable alternative to urethrotomy for kinked or entrapped catheters in the penile urethra or the urethra extending from the ischial arch. Further studies are needed to assess their safety, efficacy, and potential risks, particularly when nonstandard materials such as feeding tubes are used.

This study was conducted in compliance with the Animal Welfare Act and the National Research Council’s Guide for the Care and Use of Laboratory Animals. In the case of client-owned animals, informed consent was obtained from the pet owners for participation in the study. For studies not involving new, unproven, or comparative treatments or procedures, the contemporary standard of care was provided to each animal. All animal use in this study adhered to the acceptable practices as outlined in the American Animal Hospital Association (AAHA) policy statements. This manuscript does not describe methods involving inhumane conditions or non-compliance with the above-mentioned regulations. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science and ICT) (No. 2021R1G1A1013034).