Page 1181 - Clinical Small Animal Internal Medicine

122 Obstructive Uropathy 1119

Diagnosis medical therapy is typically insufficient to cure most ure­
VetBooks.ir Abdominal pain may be the only finding associated with teral obstructions, as the physical barrier (stone, tumor,
stricture) must be addressed.
unilateral ureteral obstruction, as the animal’s renal
Upper urinary tract calculi are typically calcium oxa­
function from the contralateral kidney should be suffi­ late, particularly in the cat, and dietary dissolution will
cient to maintain renal values in a normal range. therefore not be effective in most cases. Furthermore,
Abdominal discomfort appears to be a more easily rec­ there is insufficient time to allow dissolution to take
ognized sign in the dog than the cat. On physical exami­ place in the setting of a complete ureteral obstruction in
nation, a poor body condition may be observed if the which rapid nephron loss is occurring. In the patient
obstruction has been chronic and renal dysfunction is with ureterolithiasis, intravenous fluid therapy should be
long‐standing. It is relatively common to observe cats initiated as the animal is often dehydrated and an
with marked discrepancy in renal size on abdominal pal­ increase in urine flow may help to move the calculus into
pation, the so‐called “big kidney, little kidney” syndrome. the bladder.
This is theorized to occur secondary to prior chronic Ureteral relaxation and reduced ureterospasm can be
obstruction of the little kidney, which led to a reduction achieved by administration of an alpha‐receptor antago­
in glomerular filtration and renal blood flow, progressive nist such as prazosin (0.25–0.5 mg per cat q12h) or the
nephron loss, renal fibrosis, and compensatory hyper­ smooth muscle relaxant amitriptyline (1 mg/kg PO
trophy of the unobstructed big kidney. q24h). There are additional medications with greater uri­
Diagnostic testing involves arterial blood pressure
measurement, serum biochemical analyses to investigate nary selectivity now available on the human market,
such as tamsulosin, though there is only anecdotal evi­
the degree of renal dysfunction and concurrent disease, a dence of their use in animals. An additional strategy to
complete blood count to screen for anemia or leukocyto­ facilitate movement of ureteroliths is a mannitol infusion
sis, urinalysis and urine culture, and imaging. Abdominal (0.25‐0.5 g/kg over 20 min, followed by CRI at 1 mg/kg/
radiographs are advised to look for evidence of urolithi­ min) to promote an osmotic diuresis. Mannitol should
asis as most, at least in the cat, are calcium oxalate and be given with caution in these animals, however, as
therefore radiopaque. However, radiography is imperfect hypervolemia can develop – particularly in cats or dogs
as small stones may be missed or findings interpreted as with bilateral ureteral obstruction. In the dog, broad‐
stones may not be within the urinary tract. The presence spectrum antibiotics should be initiated as canine upper
of calculi in the kidneys, bladder, or urethra as well as the urinary tract calculi are more likely to be infected than in
relative size of each kidney can also be investigated with cats, which are typically sterile.
survey radiographs. For dogs with urothelial neoplasia, While medical therapy should be initiated once a diag­
an increased soft tissue opacity may be observed at the nosis of ureteral obstruction is made, it must be recog­
bladder trigone or prostate. Confirmation of ureteral nized that medical therapy is effective in only a small
obstruction, however, typically requires ultrasound (see portion (reported as less than 15%) of cats with obstruc­
Figure 122.9). Ultrasound should be utilized to quantify tive ureteroliths. Medical therapy should be attempted
the magnitude of renal pelvic and ureteral dilation, the for no more than 12–48 hours in animals with ureteral
presence, number, and location of uroliths throughout obstruction secondary to urolithiasis, depending on the
the urinary tract, the existence of a stricture or area of stability of the patient, with serial monitoring to evaluate
ureteral thickening, the location of a trigonal or other for progressive renal decline or movement of the stone. If
extramural lesion compressing the ureter, an assessment medical therapy is unsuccessful, or in the setting of ure­
of renal blood flow, and the presence of any free abdomi­ teral obstruction secondary to urothelial malignancy
nal fluid.
that will not respond rapidly to medical therapy, inter­
vention by surgery or minimally invasive therapy is
advised.
Therapy
Currently, noninvasive therapy for ureteral obstruction
Treatment is directed at providing the animal comfort secondary to urolithiasis involves the use of extracorpor­
and alleviating the obstruction. Analgesia should be eal shock wave lithotripsy. This treatment modality
given due to the pain associated with ureteral obstruc­ employs high‐energy shock waves directed through the
tion, related to stretch of the ureteral wall and renal cap­ body and focused at the site to pulverize the urolith into
sule resulting in activation of mechanoreceptors. Medical sufficiently small particles that can be safely passed out of
therapy should be initiated as soon as a diagnosis of ure­ the body. This is the standard of care in the treatment of
teral obstruction is made as it will be necessary to help human upper urinary tract calculi, but has not gained
stabilize the animal and may aid in alleviating the wide use in veterinary medicine. Few veterinarians
obstruction in a small proportion of cases. However, employ this therapy in cats as the small size of the feline