The procedures discussed will include in-hospital urine cultures, voiding urohydropropulsion, and esophageal feeding tube placement.
The three most common types of stones seen in dogs and cats are: Magnesium ammonium phosphate (struvite), Calcium oxalate, and Urate.
Magnesium ammonium phosphate (struvite) urocystoliths
Struvite stones are almost always associated with infection in dogs but often sterile in cats. Urine culture is essential.
1. Equipment necessary:
a. Sterile inoculating loop (0.001 ml). Disposable plastic loops may be available from your veterinary laboratory or purchased commercially.
b. Culture plates (blood agar, or ½ blood agar and ½ MacConkey). Available commercially from many sources.
2. Using sterile technique, transfer urine to sterile loop (loop may be gently shaken to remove excess urine)
3. Streak urine onto culture plate
4. Incubate culture plate at body temperature (1000F or 370C), plate should be upside down.
5. Examine plate for growth at 24 hours.
a. If negative: record results and discard.
b. If positive:
i. Determine colony count. With a 0.001 ml loop, 1 colony equals 1,000 colonies/ml; 10 colonies equals 10,000 colonies/ml; 100 colonies equals 100,000 colonies/ml. Record results.
ii. Send culture plate to lab. Note: some laboratories will not accept culture plates: dab bacteria with sterile culturette and send for antimicrobial sensitivity testing.
iii. Client invoice states that additional charges will be applied if sensitivity testing is performed (I contact the client when the culture is positive to let them know).
Management of Struvite Urocystoliths:
1. Surgical removal
2. Urohydropropulsion: can be performed to push the stone(s) back into the bladder for surgical removal (retrograde) or remove the stones from the body (antegrade).
a. Technique for retrograde urohydropropulsion (used for urethral stones): the patient is anesthetized and intubated. One assistant occludes the proximal urethra with digital pressure ventrally from the rectum. Saline is infused into the proximal urethra while occluding the tip of the penis. Sterile lubricant may be added to the saline. When the assistant feels the urethra distend, digital pressure is removed and a rush of saline (hopefully including the stone) will be felt entering the bladder. The procedure is repeated until the stone has returned to the bladder.
b. Technique for antegrade voiding urohydropropulsion (used for removal of urocystoliths): the patient is anesthetized (and frequently intubated). Full relaxation of the urethra is helpful. The patient is held in a vertical orientation allowing all stones to fall into the neck of the bladder. Gentle agitation is performed. The bladder is expressed into a bowl and the sediment examined for the presence of crystals and stones. The urethra can be catheterized and the bladder refilled to allow repeated flushings. Perform repeated radiographs and/or ultrasound examinations to determine completeness of stone removal.
i. It is reported that stones may be removed up to: male cat: 1 mm (larger if perineal urethrostomy performed), female cat: 5 mm, dogs >20 lbs: 5 mm plus.
ii. Proceed to surgery if voiding urohydropropulsion fails.
3. Medical dissolution
a. Cats (sterile): Hills's S/d (canned or dry), Royal Canin SO formula
i. Once dissolved, prevent recurrence with Hill's C/d multicare, Eukanuba Urinary S, Purina URst/ox, Royal Canin Urinary SO.
b. Dogs (usually infected): Hill's S/d diet plus appropriate antibiotic.
i. Continue antibiotic until 4 weeks after stones have dissolved.
ii. Monitor for recurrence of infection with scheduled cultures (one week, one month, and 3 months after antibiotic therapy has finished)
iii. Long term dietary therapy is generally unnecessary for infection-related stones.