Exam 4 - Urolithiasis Flashcards
____ stones generally form in alkaline urine & ______ ________ & _____ stones form in neutral to acidic urine
struvite - alkaline
calcium oxalate & urate stones
T/F: type of crystals in the urine only correlate with the type of stone only 50% of the time
true
how are uroliths named?
named based off of their mineral composition
what animals are predisposed to urethral obstruction?
males more than female
what does bladder stone formation depend on?
concentration of salts, adequate time in the urinary tract, favorable urine pH, absence of crystallization inhibitors (glycosaminoglycans), & a nidus upon which the salts crystalize (protein matrix)
urine can hold what kinds of salts during conditions of supersaturation which have the potential to form crystals?
calcium oxalate
magnesium ammonium phosphate
does crystalluria always predict the presence of stones in the bladder?
no
how does pH of urine help you determine most likely stone type?
certain stones form under certain pH conditions
struvite - alkaline
calcium oxalate & urate - neutral to acidic
why do we do a urine culture & sensitivity for patients with uroliths?
uroliths predispose the animal to UTIs - UTIs with concurrent urolithiasis are considered to be complicated
management of canine struvite stones requires appropriate abx therapy
what is the purpose of taking abdominal radiographs for a patient with uroliths? which stone types can be seen? which can’t be seen?
determine presence, number, size, & shape of stones - include urethra on the rad (for male dogs, take lateral pelvic rads with the pelvic limbs both hip extended & hip flexed)
you can see calcium oxalate, calcium phosphate, struvite, & silica
urate & cysteine
calcium oxalate & struvite most radiodense
what animals are predisposed to developing urate stones?
common in dalmations
seen in animals with portosystemic shunts & chronic hepatic insufficiency
is it okay to just do an abdominal ultrasound in a patient with uroliths and not get an abdominal radiograph? what is it useful for?
nope - can’t fully evaluate them for urethral stones
detecting small stones, radiolucent stones that may not be seen on rads, & looking for evidence of urethral obstruction
why do you need to submit all uroliths for stone analysis?
quantitative analysis tells us the composition of the stone & is used to guide therapy
what clue maybe seen on a cbc for a patient with urate uroliths that indicates an underlying disease process? what further diagnostics should you do for these patients?
microcytic anemia - portosystemic shunts
liver function testing
what imaging can be done to detect stones not visible on plain radiographs?
contrast radiography
what signalment of cat/cat breeds are predisposed to calcium oxalate stones?
persians & himalayans
indoor cats!
what is an important predisposing factor for struvite stone development in dogs?
UTIs - urease producing bacteria cause urine to become alkaline (pH > 7.0)
what are the bacterias that cause UTIs that are urease producing?
s. intermedius, proteus spp.
e. coli, klebsiella spp., & pseudomonas spp. sometimes produce urease
T/F: because of the association with UTIs, struvite stones are more common in female dogs
true
what dog breeds are predisposed to getting struvite stones?
mini schnauzers, mini poodles, bichon frise, & cocker spaniels
what are the most common shapes seen of struvite stones?
often smooth, blunt edged or pyramidal
can be jack shaped
where do struvite stones mostly form?
mostly in the bladder but can form in kidneys & ureters
what is interesting about struvite stones in cats in regards to how they form?
struvite stones form in the absence of a UTI but still form in alkaline urine
what are urate stones composed of?
ammonium acid urate
what is the common form of calcium oxalate stone seen in dogs?
calcium oxalate monohydrate
T/F: although hypercalcemia can predispose animals to calcium oxalate stones, most dogs are normocalcemic
true
a urine pH of what favors the formation of calcium oxalate stones?
< 6.5
what signalment of dogs are predisposed to calcium oxalate stones? what breeds are predisposed to getting them?
male dogs - often older, 8-12 years old
mini schnauzers, standard schnauzers, mini poodles, yorkies, lhasa apsos, bichons, & shih tzus
T/F: in dogs that have calcium oxalate stones, it is rare that they have a concurrent UTI
true
what is the common appearance of calcium oxalate stones?
often rosette (jagged) but can be smooth
there is an increased incidence in urate stones in what animals?
dogs with liver dysfunction (especially shunts) such as mini schnauzers, yorkies, & pekingese
dalmatians (especially males) & english bulldogs due to altered metabolism of uric acid
what do urate stones look like?
often small & can be jack shaped
yellow-brown or green & color
how are mixed stones named?
if a stone is compromised of >70% of one type of mineral, it is named for that mineral
if there is less than 70% of one stone type, considered a mixed stone
what is an example of how mixed stone may be unevenly mixed or deposited in layers?
calcium oxalate stone may be present which predisposes an animal to infection with urease-producing bacteria which makes the urine alkaline - the stone then can develop an outer layer of struvite
what is cystinuria?
inherited renal tubular transport disorder that predisposes an animal to cysteine stone formation
what breeds are predisposed to cysteine stone development?
english bulldogs, newfoundlands, dachshunds, irish terriers, basset hounds, & bull mastiffs
T/F: cysteine crystalluria is always abnormal & should be investigated
true
when would voiding urohydropulsion be an appropriate treatment choice for a patient with uroliths?
for small bladder stones with clinical signs - urethral size will dictate if this is possible!!!
stone must be <7mm in female dogs, <5 mm in male dogs, & <5 mm in female cats
when is the only time you could use voiding urohydropulsion for a male cat with uroliths?
only if they have had a perineal urethrostomy surgery
what are potential complications that may arise when using voiding urohydropulsion as a way to remove uroliths?
urethral obstruction, bladder rupture, & hematuria
how is voiding urohydropulsion done to remove uroliths?
patient is anesthetized, bladder is distended with saline, urinary catheter is removed, patient is held upright, & steady pressure is applied to the abdomen
procedure is repeated as needed - stones are collected for submission
when is catheter-assisted retrieval appropriate to use for removing uroliths? how is it done?
very small bladder stones - may not require sedation
u cath is placed & bladder is filled with saline - saline is suctioned via the catheter may contain stones
is it okay to use voiding urohydropulsion in a patient that had recent bladder surgery?
NOPE
what is the benefit of using medical dissolution for treating uroliths?
less invasive than a cystotomy & avoids placement of suture that can induce stone formation
cost of medical management & follow up is similar to a cystotomy
T/F: medical dissolution can be used for calcium oxalate stones
false!!! can’t be used!!!!
what is the treatment of choice for non-obstructive struvite uroliths located in the bladder?
medical dissolution
what is the protocol for struvite stone dissolution?
for dogs - abx based on culture & sensitivity are continued throughout dissolution period (in cats, struvite stones are usually sterile)
what diets must be fed for dissolving struvite stones in dogs & cats?
dogs - hill’s urinary s/d canned or royal canin urinary s/o canned and dry
cats - hill’s urinary care s/d canned & dry, hill’s urinary care c/d canned & dry, & royal canin urinary s/o canned & dry
if medical dissolution therapy is unsuccessful for struvite stones, what should you consider?
were the owners compliant with the diet? urine should be isosthenuric & pH should be < 6.5
was abx therapy appropriate? reculture
stone may contain mineral that can’t be dissolved
may fail if solitary stone is very large & filling the entire bladder lumen
what are some contraindications for stone dissolution of struvite uroliths?
urethral obstruction
discomfort for the patient
very young or lactating patients
what are the risks involved in doing a cystotomy for removing uroliths?
experienced surgeons fail to remove all uroliths in 15% of dogs & 20% of cats - to fix this, do rads post-op
suture material in the lumen of the bladder can act as a nidus for stone formation
when is a cystotomy indicated?
for calcium oxalate stones or other stones in patients that medical management isn’t an option
when would you consider leaving uroliths in a patient?
stones that are sterile, asymptomatic, not dissolvable, & large enough that obstruction isn’t a concern
risk of secondary UTI, polyp formation, & patient discomfort
client must be educated about signs of obstruction
how should you attempt to unblock an animal?
attempt to pass a lubricated ucath alongside the stone to empty the bladder
retrograde hydropulsion can be used to try & dislodge the stone & flush it into the bladder & then it can be removed with cystotomy or lithotripsy
what is lithotripsy? when is it best used?
urolith is fragmented into pieces that can be hydropulsed or retrieved endoscopically
best for a single stone whose fragmented pieces can be hydropulsed out without excessive trauma to the urethra of urethral obstruction
when is endoscopic basket retrieval of uroliths indicated? what animals can’t have this?
for stones or stone fragments < 5-7 mm
not suitable for male cats or small male dogs
what is the common urolith type that often causes ureteral obstruction?
usually due to calcium oxalate stones
why do you need immediate treatment for ureteral obstruction?
need urgent treatment because obstructive or partially obstructive ureterolith causes acute kidney injuries
how is ureteral stenting done?
stent is placed from the bladder to the kidney bypassing the obstructing stone & causing passive dilation of the ureter (usually for dogs)
what medical management is used for ureteral obstructions?
iv fluids, mannitol as a diuretic, prazosin (alpha adrenergic blocker, to decrease ureteral spasm), & analgesia
close monitoring
if no improvement after 24 hours, move to alternative treatment plans
concurrent UTIs are common in dogs with ureteral obstructions
how is a subcutaneous ureteral bypass system performed to correct ureteral obstructions?
special device is surgically placed that connects the kidney to the bladder external to the ureter (usually for cats)
what is a nephrostomy tube?
in kidneys with complete obstruction, a tube can be placed into the kidney & connected to an extension system outside of the body to buy time until a definitive therapy can be performed within 24 hours
how are struvite stones prevented?
manage UTIs (dogs > cats)
correct/manage underlying disorders that predispose an animal to UTIs
avoid meds that predispose animals to UTIs
dietary management for prevention of sterile struvite stones (diets restricted in phosphorus & magnesium to help produce more acidic urine) or consider a canned diet to increase water intake & decrease USG
what medications may be used for preventing struvite stones?
consider methionine or ammonium chloride to acidify urine if no UTI is present
abx to manage UTIs
what monitoring can be done for preventing struvite stone formation?
urinalysis monthly to start & then every 3-6 months
target pH <6.5
target USG < 1.020-1.030
urine culture monthly for 2-3 months & then every 3-6 months in cases with UTI related stones
culture if signs of UTI develop
imaging if clinical signs of stones develop
T/F: if a UTI is present, it is a complication of calcium oxalate urolithiasis, not the cause
true
what dietary management is used for preventing calcium oxalate stones?
avoid foods high in oxalate, avoid calcium supplements, feed canned food to increase water intake (target USG in dogs <1.020, in cats <1.030)
reduced protein diets to promote diuresis & alkaline urine formation
what are your diet options for a patient with calcium oxalate stones?
dogs - hill’s u/d canned & dry, hill’s g/d, royal canin urinary s/o canned & dry
cats - hill’s c/d multicare canned & dry, royal canin urinary s/o canned & dry, IAMs urinary o-modrate pH canned & dry, & purina UR urinary st/ox canned & dry
why does limiting dietary calcium not help with preventing calcium oxalate urolith stone formation?
in the gi tract, calcium & oxalate bind which limits oxalate absorption
if dietary calcium is restricted there is more unbound oxalate which is absorbed
what is the purpose of using potassium citrate for a patient with a history of calcium oxalate stones?
alkalinize the urine
if the urine pH is consistently <6.5 (however, pH is less important for calcium oxalate stone formation)
may inhibit crystallization of calcium oxalate & favor formation of calcium citrate in urine
what is the purpose of using hydrochlorothiazide for a patient with a history of calcium oxalate stones?
increase renal tubular resorption of calcium
used for patients with highly recurrent calcium oxalate stone formers that are not hypercalcemic
what monitoring is done for patients with a history of calcium oxalate stone formation?
urinalysis every 3-6 months to target a pH of 6.5-8 & usg < 1.020 for dogs & < 1.030 for cats
imaging every 6-12 months to detect stones while small enough to remove them with hydropulsion
imaging if signs of uroliths develop
for patients without underlying liver disease, what monitoring & prevention can be done to prevent the formation of urate uroliths?
dietary management - low protein/purine diets (hill’s u/d, hill’s l/d, royal canin hepatic ls) & increase water intake
medications - allopurinol used in cases in which dietary therapy alone is not effective but must be combined with a low purine diet or will predispose them to xanthine stone formation & potassium citrate may be added to achieve a urine pH > 7.0
monitoring - urinalysis monthly then every 3-6 months with a goal of pH > 7 & usg < 1.020 for dogs & < 1.030 for cats
imaging (ultrasound or contrast rads) every 3-6 months
