Clinical History
The dog was presented with dysuria and haematuria for a duration of two weeks. On palpation of the bladder numerous stones could be felt. The owner was warned that surgery would be needed and the risks of general anaesthesia in an obese animal were explained. The dog was booked for radiography and surgery the following day and was given a course of tablets containing trimethroprim 80mg and sulphamethoxazole 400mg (Co-Trimoxazole, Regent), to be given half a tablet twice daily.

Radiography
On 23/12/98 the dog was admitted for a general anaesthetic, having been starved over night with access to water two hours prior to surgery. A pre-anaesthetic check revealed no thoracic or cardiovascular abnormalities. Temperature was 38.2 C, pulse 114 per minute and respiration 31 per minute. The owners signed a consent form and the dog was premedicated with 0.6 mg acepromazine (ACP, C VET) by subcutaneous route, 45 minutes prior to surgery.

Induction was achieved using 175 mg thiopentone sodium 2.5% (Intraval Sodium, Rhone Merieux) and a cuffed size 7.5 endo-tracheal was used to intubate. The dog was placed on a semi-closed parallel lack circuit with flow rates of 4 litres of nitrous oxide and 2 litres of oxygen and 1.5% halothane. A 23g intravenous catheter was placed aseptically into the cephalic vein and a slow infusion of 500 mls Hartmann's was started. Analgesia was given with 3 mg morphine sulphate by intra-muscular route. Antibiotic cover was provided with 165 mg trimethoprim-sulphadiazine 7.5% (Borgal, Hoescht Roussel) given intra-venously.

A radiograph of the abdomen in right lateral recumbency was taken to confirm the location of the uroliths, including the kidneys. The radiograph revealed that all the uroliths were located in the bladder. See radiograph 1 above.

Surgical preparation
The ventral abdomen was prepared, as in the first paragraph of Appendix 1, covering an area from the ziphisternum cranially to the vulva caudally, and laterally 10 cms either side of the midline. The dog was moved to theatre and placed in dorsal recumbency (supported by a cradle) with both hind legs extended and tied out. The ECG electrodes were attached on the limbs just proximal to the stifle and olecranon. Skin cleansing took place as described in the second paragraph of Appendix 1.

Surgery
The area of the incision site was then draped by the scrubbed surgeon using four barrier drapes arranged in a quadrant, leaving only the midline exposed. See figure 1 on the right.

The instruments in this procedure included two standard surgical kits, as described in Appendix 2. In addition to this a sterile bowl, two 20 ml syringes, a 23 g needle, sixteen swabs and 0.9 % saline were used.

An incision was made through the skin and subcutaneous tissue along the midline, starting 2 cms cranial to the pubic symphysis and extending for 10 cms. Blunt dissection revealed the abdominal wall which was grasped with rat toothed forceps and lifted. A stab incision was made through the tissue and blunt mayo scissors were used to lengthen the incision to the extent of the skin incision. The bladder was located and lifted out of the abdomen, reflected caudally and laid on swabs. A stay suture using 3 m monofilament nylon (Monilon, Arnolds) was placed in the cranial bladder. Other swabs were then packed in the abdominal wound to minimise contamination by the bladder contents. Cystocentesis was performed with a 20 ml syringe and 23 g needle to remove as much urine as possible. A 2 cm incision was made into the dorsal aspect of the bladder, taking care to avoid the visible blood vessels. Numerous uroliths, ranging from 1 mm to 1.4 cms, were removed from the bladder. See Figure 2 below.

The bladder was then flushed using a sterile 20 ml syringe and sterile saline to ensure all uroliths had been removed. The bladder was closed with 2 m polyglactin 910 (Vicryl, Ethicon) on a round bodied needle using a double layer of simple interrupted sutures, the first layer including the mucosa and submucosa and the second including the muscularis and serosa.

All used swabs were removed and counted, the bladder replaced within the abdomen and the abdominal cavity was flushed with 0.9% saline. At this time the surgeon changed surgical gloves and a fresh surgical kit was used to close the abdominal wound. The abdominal wall was closed using 3 m polydioxanone (PDS II, Ethicon) on a cutting needle with simple interrupted sutures. The subcutaneous tissue was closed with 3.5 m chromic catgut (Ethicon) on a cutting needle using a simple continuous suture. Skin was closed with 3 m polyamide (Nylonamide, Animus) on a cutting needle using horizontal mattress sutures.

Post-operative period.
Recovery was uneventful, the dog being in sternal recumbency within 30 minutes of the end of anaesthesia. On recovery the dog was given 24 mg of ketoprofen (Ketofen 1%, Rhone Merieux) by intramuscular route. The dog was sent home later in the day with 2 Ketofen 20 mg tablets, half to be given daily with food, to start the following day. The owners were advised to watch for urination and revisit in the morning if the dog could not urinate. They were also told to expect haematuria and that they should finish the course of antibiotics previously prescribed for the dog. The calculi were sent off for analysis to the Minnesota Urolith Centre, University of Minnesota, USA. The dog returned 3 days later for a satisfactory post-operative check and the sutures were removed after 10 days. The owners were then told to revisit when the results of the calculi analysis returned.

Discussion
There are many causes of urolithiasis, including genetics, diet, obesity, inactivity, infectious agents or systemic disease. Therefore surgical removal of uroliths is not a cure. The owner was warned that, as uroliths reform in 1 in 4 dogs, (Hills Pet Products Data Sheet), permanent dietary management would be necessary for the dog. In this particular case, despite the bladder being full of calculi, the radiograph showed none in the urethra and the bitch was still able to pass urine with difficulty. Male dogs are more susceptible to obstruction of the urethra by calculi due to natural constrictions in the urethra - the most important being at the site of the os penis.

Results from Minnesota showed that the chemical composition of the uroliths was comprised of both calcium phosphate and magnesium ammonium phosphate. Some types of calculi, eg struvite (magnesium ammonium phosphate) can be dissolved by dietary management and treatment with antibiotics of the urinary tract infection which usually precedes formation of struvites (Minnesota Urolith Centre).Therefore it would be advisable to send off a urine sample for bacterial culture to ensure the correct antibiotic was used. This type of treatment would be suitable for male cats after placement of a urinary catheter due to obstruction by calculi. Manufacturers, eg Hills, produce a diet called s/d which is low in protein, magnesium, phosphate, high in sodium and produces acid urine. This diet is intended for short term use for the dissolution of struvite calculi. Struvites form in alkaline urine but become highly soluble in acid urine below pH 6.4. Hills also produce a long term maintenance diet which is called c/d to maintain acidity of the urine, to prevent struvites reforming. Other diets are available for different types of calculi. There is no dissolution diet available for calcium phosphate. Dissolution was not an option in this dog's case due to amount and size of calculi and condition of the dog.

Complications of this type of surgery include contamination of the abdomen, which could result in peritonitis. Therefore great care has to be taken to avoid spillage of urine into the abdominal cavity. Another post-operative complication is failure to remove all calculi, resulting in further obstruction. Prior to closure of the bladder the urethra should be flushed with sterile saline to ensure removal of all calculi. Other considerations in this type of surgery which involves large amounts of flushing with saline involve bacterial strike through via wet drapes and hypothermia of the patient due to excessive wetting of the skin, causing temperature loss through evaporation. Barrier drapes are essential to avoid both of these from ocurring. Also, saline should be heated to body temperature before flushing as this will help preserve body temperature. Water heated pads are not available in this clinic but bubble wrap was used to wrap limbs prior to surgery in order to conserve body temperature.

With regard to analgesia, carprofen would have been the choice of non steroidal anti- inflammatory drug, as it is the only one of the group which is considered safe to use peri-operatively due to its lack of effect on the body's prostaglandin production. However, due to a manufacturing problem it was not available at the time of surgery and ketoprofen was used as the NSAID. This could not be administered peri-operatively due to its adverse effects on prostaglandin production, possibly causing renal failure or ulceration of the GI tract. Therefore morphine was selected for intra-operative use, in conjunction with nitrous oxide. It would have been preferable for the morphine to be given in the premedication to allow it to be active at the time of the first incision. The only disadvantage of giving morphine pre-operatively is that vomiting can occur shortly after administration - this is rarely a problem in a conscious animal.

A blood sample was taken to check the function of the parathyroid gland, as this is recommended in cases of calcium phosphate calculi, as excess levels of calcium are thought to be the precursor to these calculi. However, the results of the blood sample showed normal levels of calcium (2.4 mmol/l). Therefore the owner was told to feed Hills s/d exclusively for 2 months and then to change to Hills c/d diet permanently. The owner could also have been told to check the pH of the dog's urine daily and to revisit if the urine showed alkalinity for more than 2 days. (Manual of Canine and Feline Nephrology and Urology, BSAVA).

References:
Anatomy of the Dog, Miller, Saunders 2nd Ed 1979, Ch 9.
Current Techniques in Sm An Surg, Bojrab, 3rd Ed, Lea & Febiger 1990.
Clinical Management of Canine & Feline Urolithiasis, Hills 1991.
Minnesota Urolith Centre, Clinical Data Sheet Rev 1996.
Manual of Can & Fel Nephrology & Urology, BSAVA 1996, p 216,217.