Page 800 - Small Animal Clinical Nutrition 5th Edition

830 Small Animal Clinical Nutrition

Box 38-2. Principles of Urolith Treatment and Prevention.
VetBooks.ir OVERVIEW talloids are dissolved or suspended and 3) reducing the quantity of

Surgery has been the time-honored method of managing all types of lithogenic crystalloids in urine. For example, attempts to increase the
urolithiasis in dogs. Although surgery has been an effective method solubility of crystalloids in urine often include administration of med-
that provides immediate elimination of uroliths, it is associated with ications designed to change urinary pH to create a less favorable
several limitations, including: 1) persistence of underlying causes environment for crystallization. Likewise, diuresis is commonly
and a high rate of recurrence of uroliths despite surgery, 2) patient induced to increase the volume of urine in which crystalloids are dis-
factors that enhance adverse consequences of general anesthesia solved or suspended. A dietary change is an example of a method to
or surgery and 3) inability to remove all uroliths or fragments of reduce the quantity of lithogenic crystalloids in urine.
uroliths during surgery. In addition, situations occasionally arise in In general, dietary and medical treatment should be formulated in
which owners of companion animals will not consent to surgical stepwise fashion, with the initial goal of reducing the urine concen-
therapy but will consider dietary and medical therapy. Dietary and tration of lithogenic substances. Medications that have the potential
medical dissolution of uroliths may be considered for these and to induce a sustained alteration in body composition of metabolites,
other reasons (i.e., the urolith is asymptomatic). in addition to urine concentration of metabolites, should be reserved
Results of several experimental and clinical investigations have for patients with active or frequently recurrent uroliths. Caution must
confirmed the efficacy of dietary and medical dissolution of canine be used so that the side effects of treatment are not more detrimen-
uroliths. Despite the feasibility of dissolution of uroliths, however, this tal than the effects of the uroliths.
form of therapy is associated with potential hazards. Uroliths always Results of experimental and clinical studies have revealed that the
predispose patients to urinary tract infection (UTI) and obstructive size and number of uroliths do not dictate the likelihood of response
uropathy. Risks and benefits of dietary and medical vs. surgical and to therapy. We have had success in dissolving uroliths that are small
dietary and medical therapy must be considered for each patient. and large, single and multiple. However the rate of dissolution is
Detailed descriptions of nonsurgical and surgical methods for related to size and surface area of the urolith exposed to urine. Just
reestablishing urine outflow are beyond the scope of the discussion as one large ice cube dissolves more slowly than an equal volume of
but are available elsewhere. Likewise, details pertaining to surgical crushed ice, one large urolith will dissolve more slowly than an equal
removal of uroliths, endoscopic and percutaneous manipulation of volume of many smaller uroliths. Rate of dissolution is influenced by
uroliths, chemolysis via nephrostomy, disintegration of renal and surface area of the urolith exposed to undersaturated urine.
ureteral uroliths via ultrasound and shockwave lithotripsy have been Difficulty in inducing complete dissolution of uroliths by creating
reviewed. urine that is undersaturated with the suspected lithogenic crystalloid
should prompt consideration that: 1) the wrong mineral component
DIETARY AND MEDICAL DISSOLUTION OF UROLITHS was identified, 2) the nucleus of the urolith is of different mineral
Therapy should not be initiated before appropriate samples have composition than outer portions and/or 3) the owner or the patient is
been collected for diagnosis. The objectives of dietary and medical not complying with therapy.
management of uroliths are to arrest further growth and to promote
urolith dissolution by correcting or controlling underlying abnormali- SURGICAL REMOVAL OF UROLITHS
ties. For therapy to be effective, it must induce undersaturation of Detection of uroliths is not in itself an indication for surgery.
urine with lithogenic crystalloids by: 1) increasing the solubility of However, along with dietary and medical management, surgical
crystalloids in urine, 2) increasing the volume of urine in which crys- intervention may play an important role in therapy of urolithiasis.

position of uroliths. Because a variety of different types of with an outer shell composed primarily of calcium apatite. Dif-
uroliths and nephroliths occur in dogs (Tables 38-8 and 38-9), ficulty will also be encountered in attempting to induce com-
veterinarians should use a protocol that facilitates determina- plete dissolution of a urolith with a nucleus of calcium oxalate,
tion of the mineral composition of uroliths based on probabili- calcium phosphate, ammonium urate or silica and a shell of
ty (Tables 38-10 and 38-11). Formulation of dietary and med- struvite because the solubility characteristics of this combina-
ical therapy based on the mineral composition of uroliths deter- tion of minerals are dissimilar. These phenomena should be
mined by this protocol is usually associated with a high degree considered if dietary and medical therapy seems to be ineffec-
of success in dissolving uroliths or arresting their growth. tive after initially reducing the size of uroliths (Box 38-2).
Attempts to induce dissolution of uroliths may be hampered
if the uroliths are heterogeneous in composition. This has not
been a significant problem in dogs with uroliths composed pri- REFERENCES
marily of magnesium ammonium phosphate with small quan-
tities of calcium apatite because the solubility characteristics of The references for Chapter 38 can be found at
the two minerals are similar. Veterinarians have encountered www.markmorris.org.
difficulty in dissolving uroliths composed primarily of struvite