Etiology

For stone formation to occur it requires saturated urine dependent upon urine pH, and the concentration of the solute.
Different types of stones are:

• Struvite, which is made up of magnesium ammonium phosphate. They are found in highly alkaline urine and often a concurrent urinary tract infection is present. They tend to be the most common type of urolith.
• Calcium oxalate, and Cystine, found in acidic urine.
• Ammonium acid urate, and Silicate uroliths, found in neutral to acidic urine.

The presence of clinical signs depends on the obstruction of urine, the presence of infection, and edema (swelling). Stones that cause obstruction to the flow of urine set up an environment of urine stasis and bacterial growth. The irritation caused by the stones results in secondary infections leading to pyelonepthritis (inflammation of the kidney) an upper urinary tract infection, or cystitis (inflammation of the bladder) and urethritis (inflammation of the urethra) a lower urinary tract infection.

Pain becomes present when a stone or stones produce an increase in hydrostatic pressure and distend the renal pelvis (hydronephrosis). Pain may seem sudden and appear to move downward from loin region towards the bladder or, in males, the testicle. This type of pain is often termed renal colic. When stones block a ureter, acute colicky type pain is noticed. The rat may have and urgency to urinate, to lick at genitals, or to nip at self due to pain. Little if any urine may be passed and drops of blood may be seen due to the stones abrasive action when the urine is attempting to pass out through the urethra.

Though the cause of stone formation is hard to determine, some factors include a genetic predisposition , metabolic disorders such as diabetes, myelloproliferative disease like leukemia, or hypocalcaemia (abnormally high amounts of blood calcium), diet imbalance, a poor intake of water, parasites such as bladder thread worm , and bacterial infections such as E. coli , klebsiella, staphylococcus, or mycoplasma.

Other conditions that can lead to stone formation due to the retention and stasis of urine are anatomical defects, or pocketing in the bladder wall known as diverticula, and immobility due to stroke and hind limb paralysis.

Stones are often more commonly found in males than females due to a longer urethra. Also, once stone formation has been found to exist, and if treatment is able to resolve the stones that are present, it is known that there is still a high rate of recurrence.

The treatment for stones depends on their type and location in the urinary tract. In some cases antimicrobials are used to help dissolve stones. In cases where the antimicrobials alone will not resolve the stones because they are too large or too many, the following surgical procedures may be used: a cystotomy for extracting bladder stones, a urethotomy for extracting stones obstructing the urethra, or a nephrotomy for extracting stones from the kidney. Removing lodged stones from the kidney, ureter, or urethra in rats is difficult at best though not impossible. Without treatment or the ability to be able to remove the stones that cause complete blockage of urine flow, renal failure quickly develops and death rapidly follows. Euthanasia may need to be considered where pain can not be resolved or the quality of life becomes a factor.

Photos of stone formation and case history can be seen in the following figures.

• Fig. 1: Case history and bladder stones.
• Fig. 2 Necropsy photos (graphic) of bladder stones.

Diagnostics

Palpate bladder to determine distention.

Obtain urinalysis, and culture.

Obtain abdominal x-ray.

CBC for signs of dehydration or infection.

Electrolytes or Biochem profile for signs of hypocalcaemia, hyperkalemia, azotemia.

Treatment

Provide sedative, or muscle relaxant to control pain.

Give IV or SQ fluids if dehydration is present. Fluid therapy should be conservative until obstruction relieved and there is urine output.

Evaluate if surgery is practical to remove bladder stones or blockage.

Treat underlying disease processes that may be present, such as diabetes.

Treat urinary tract infections with antimicrobials such as:

• enrofloxacin
• tetracycline
• trimethoprim sulfa
• chloramphenicol
• gentamicin

For more information on medications refer to the Rat Medication Guide

If alteration in nutrition required instruct to reduce amount of protein and calcium content in diet.

Discuss euthanasia if quality of life impaired.

Nursing Care

Outcome

Prevention

Posted on November 22, 2003, 15:40, Last updated on June 16, 2008, 19:21 | Urinary / Renal