Page 1212 - Clinical Small Animal Internal Medicine

1150 Section 10 Renal and Genitourinary Disease

appropriate antimicrobials. For dissolution to occur, the alternatives include amitriptyline, alpha‐adrenergic
VetBooks.ir uroliths must be surrounded by undersaturated urine to antagonist therapy (prazosin or tamsulosin), or glucagon
therapy.
allow them to go back into solution. For these reasons,
Intermittent hemodialysis has been reported to resolve
urocystoliths and nephroliths are amenable to dissolu­
tion but ureteroliths and urethroliths are not. Dissolution acute kidney injury secondary to obstructive uretero­
of struvite nephroliths has been reported in six dogs that liths. Thirteen cats did not have any surgical intervention
had bacterial pyelonephritis and impaired urine‐concen­ and eight of these 13 survived 365 days or longer past
trating ability. An average of 184 days of treatment discharge; all of these cats had a degree of renal recovery
(range, 67–300 days) with a calculolytic diet (Hill’s sufficient for discontinuation of IHD prior to hospital
Prescription Diet Canine s/d) and antibiotic therapy was discharge.
required for radiographic dissolution of the stones in If medical management fails or the patient is unstable
these dogs. In the author’s experience (AB), ureteroliths (e.g., hyperkalemic, overhydrated, oligo‐/anuric, devel­
should be dissolved within 2–6 weeks and nephroliths oping progressive hydronephrosis), or if IHD is not
should be decreased in size (<75 % initial size) by three available at the institution, immediate renal decompres­
months. It can take up to nine months to dissolve large sion should be considered. If minimally invasive urolith
nephroliths. Increasing the number of walks per day extraction or bypass is not possible, then the two best
should be encouraged to improve stone elimination. options are to (1) place a nephrostomy tube or (2) initi­
Aggressive diuresis has been effective at helping move ate IHD or continuous renal replacement therapy
ureteroliths down into the bladder and in resolving (CRRT), for stabilization. Immediate renal pelvis
azotemia in 8–14% of cats with ureteroliths. This lim­ decompression is recommended over hemodialysis or
ited success rate of diuresis may be explained by the high CRRT if the patient is stable enough to undergo anes­
percentage of ureteral obstruction secondary to stric­ thesia and the operator is comfortable with the proce­
ture in cats. dure. Renal pelvis decompression halts the damage
Surgical management was effective in 101 cases, but being done by the increased hydrostatic backpressure,
has a high postoperative complication rate (31% in cats whereas hemodialysis stabilizes a patient while the ure­
and ~35% in dogs) and perioperative mortality rate (18% teral obstruction persists, resulting in ongoing renal
in cats and 25% in dogs). Medical management should be injury. A short delay in treatment in a stable patient is
considered prior to surgical intervention; however, more preferred over immediate treatment by an inexperi­
aggressive management should be considered if the enced operator, as the complication rates with any of the
patient fails to improve with medical management alone decompression procedures are high if experience is lim­
for 48 hours, or if the patient is anuric/oliguria, hyper­ ited. Partial obstructions allow a longer window of
kalemic, overhydrated or if there is progressive renal pel­ opportunity for treatment without such dramatic renal
vic dilation. damage as seen with complete obstructions, allowing
In the authors’ experience, aggressive diuresis in cats time to arrange referral to a facility with experience in
appears to be more effective for small stones (<1–2 mm) these procedures. Over 75% of obstructed feline patie­
in the distal third of the ureter compared to larger stones, nts have a partial ureteral obstruction based on
or those in the proximal ureter. Aggressive diuresis con­ ureteropyelography.
sists of aggressive IV fluid therapy while monitoring Many patients with ureteral obstruction have concur­
central venous pressure, body weight, electrolyte con­ rent urinary tract infections (75% of dogs and 10–30% of
centrations, and hydration status. One recommended cats) so broad‐spectrum antimicrobial therapy is recom­
fluid therapy protocol includes administering 0.45% mended for all patients, and a urine culture and sensitiv­
saline mixed with 2.5% dextrose at a maintenance rate ity should be part of the work‐up.
(e.g., 50–60 mL/kg/d). Additionally, a replacement fluid
such as Plasma‐Lyte® (Abbott Animal Health) or lactated Surgical Removal of Upper Urinary
Ringer’s solution (avoiding saline, if possible, to reduce Tract Uroliths
sodium load) is administered to correct dehydration and
promote diuresis (e.g., 45–75 mL/kg/d). The maximum Nephroliths
combined fluid rate should not exceed 120 mL/kg/day. In In small animals, traditional intervention for treatment
patients without cardiac compromise, mannitol is of nephrolithiasis involves a nephrotomy, pyelotomy, or
administered as a bolus at 0.25–0.5 g/kg over 20–30 min­ salvage ureteronephrectomy. Complications can be
utes followed by a constant rate infusion of 1 mg/kg/min severe and life‐threatening after a nephrotomy, including
for 24 hours. If, after 24 hours, there is no evidence of hemorrhage, decreased renal function, ureteral obstruc­
improvement based on imaging and serial bloodwork, tion by remaining nephrolith fragment passage, and uri­
the mannitol infusion is discontinued. Other medical nary leakage into the abdomen from the renal incision.