Urinary catheterisation is a common veterinary procedure performed to collect sterile urine, empty the bladder or relieve urinary obstruction. Veterinarians will normally choose a catheter depending on the size of the dog and the purpose of the catheterisation. If the catheter is meant to stay in the bladder, smaller, flexible catheters are commonly used. Larger, sturdier catheters are chosen if the purpose is to aspirate urine quickly or to push past a urinary obstruction. Because this procedure is painless, most male animals will not need sedation or anaesthesia. Females may need sedation because of the intrusive nature of the act.
The veterinarian will typically have a veterinary technician place the male dog on his side and abduct the upper rear leg, exposing the prepuce (the skin covering the penis) and the penis. The tech will then retract the prepuce and present the glans penis (the tip of the penis). The glans penis and the prepuce are gently washed with a warm, dilute antiseptic solution and rinsed with warm water or sterile saline. The veterinarian will open the top of the package containing the catheter and apply sterile, water-soluble lubricant to the catheter tip. If the vet is wearing sterile gloves, he will remove the catheter from its wrapper. If he chooses not to wear gloves, the catheter will be advanced through the packaging and handled aseptically.
The tip of the catheter will then be gently inserted into the urethral opening. As the vet slowly advances the catheter through the urethra, he may encounter slight resistance at the os penis (the small bone found in the canine penis) or the area of the urethra that curves around part of the pelvis called the ischial arch. Using steady, gentle pressure, the veterinarian will normally push past this and feed the catheter into the neck of the bladder. Urine should begin to flow into the catheter as it advances into the bladder for approximately one more centimetre. A large, sterile syringe is attached to the end of the catheter and urine drawn out of the bladder. The vet will continue to aspirate urine until the bladder is empty, measuring the contents of the syringe to quantify the amount. At this point, he will remove the catheter.
If the catheter is meant to be indwelling, the vet will suture it to the prepuce using bandage tape and nylon suture material. The end of the catheter will be attached with tubing to a measurement bag and the animal will be placed in a cage with the bag hanging down so that gravity can draw urine out of the body. Urine output will be measured periodically and noted in the patient's record. This is usually done in animals with a history of urethral obstruction or in dogs that can't stand to urinate.
The female dog is prepared exactly the same as the male, except that she may be standing, on her side or lying on her stomach with her hind legs dangling off the end of the examination table. A technician will wash her vulva with a gentle, antiseptic solution and rinse with sterile saline or water. As the tech holds the tail out of the way, the veterinarian will introduce one millilitre of 2 per cent lidocaine gel (a local anesthetic) to the vaginal floor. Wearing sterile gloves, the veterinarian will insert a lubricated finger into the vaginal opening until he feels the external urethral opening. If he can't find the opening by feel, a large, lighted otoscope (the instrument used during ear exams) will be placed in the vagina to allow the vet to find the urethra. A sterile catheter with sterile, water-soluble solution on its tip is then introduced into the vagina and advanced through the urethra until it enters the bladder. Urine will be withdrawn into a sterile syringe and the catheter removed or, if it is meant to be indwelling, the catheter will be attached to her body and a urine collection device placed on its free end.