Once the animal has been hydrated, urine flow should rapidly increase to 2-5 ml/kg per hour, depending upon the rate of IV
fluid administration. If urine production is not sufficient, the animal's circulating blood volume should be assessed first.
If the animal is normovolemic, the rate of fluid administration should be slowed to prevent overload. An indwelling urinary
catheter should be placed if not already present. Calculation of "ins and outs" can then be used to provide appropriate quantities
of IV fluids to match urine output. The maintenance fluid requirement (estimated at 20 ml/kg/day for insensible losses) is
calculated for a short interval of time, typically four hours. The volume of urine during the previous interval is added to
the maintenance amount, giving the volume of IV fluids to be administered over the subsequent four-hour period. This helps
maintain hydration while minimizing the risk of fluid overload.
Specific therapy to increase urine flow is administered concurrently. Diuretics are administered first. Furosemide has traditionally
been administered as escalating bolus doses. However, a loading dose of 0.66-1.0 mg/kg, followed by continuous rate infusion
(CRI) at 0.66-1.0 mg/kg/hr, has been shown to be more effective in producing diuresis in normal dogs.
If furosemide fails to increase urine flow, osmotic diuresis with hypertonic mannitol solutions can be attempted. However,
this is contraindicated in oliguric animals that are already volume overloaded because it will result in increased serum osmolality,
circulating blood volume and blood pressure. Ten percent or 20 percent mannitol can be given as a bolus dose of 0.5-1.0-g/kg
body weight over 15 to 20 minutes. If effective, urine flow will increase within one hour. Repeat bolus doses can then be
administered every four to six hours, or it can be administered as a constant-rate infusion at a dose of 1-2 mg/kg/minute.
Mannitol may have additional beneficial effects in addition to its action as a diuretic. It inhibits renin release because
of its hyperosmolar effect on tubular luminal filtrate. In addition, it acts as a free radical scavenger, blunts damaging
increases in intramitochondrial calcium and may result in a beneficial release of atrial natriuretic peptide.
Dopamine infusion traditionally has been recommended for oliguric or anuric animals. Dopamine stimulates two types of dopamine
receptors (DA-1 and DA-2) as well as alpha- and beta-adrenergic receptors.
In dogs, it causes an increase in renal blood flow (RBF) and urine volume; glomerular filtration rate (GFR) either increases
or is unchanged. In cats, increased urine production occurs in the absence of increases in RBF or GFR. This is most likely
due to alpha-adrenergic stimulation that increases cardiac output and blood pressure, and induces natriuresis.
The use of dopamine has become somewhat controversial, because studies of its benefit in people with or at risk of ARF have
failed to demonstrate improvement in clinical outcome despite transient improvement in urine output.
There is little or no documentation of the efficacy of dopamine in dogs and cats with ARF. It may have some benefit in dogs
with oliguria or anuria, because increasing urine production is beneficial in managing fluid therapy. Its use in cats is less
clear, because the higher doses necessary to promote urine production may result in adverse physiologic consequences that
may negate its benefit.
For dogs, dopamine is diluted in an isotonic fluid and administered as an IV infusion at the rate of 0.5-3 mcg/kg per minute.
High rates of infusion (greater than 10 mcg/kg per minute) may cause arrhythmias, increased blood pressure and vasoconstriction.
Dopamine is inactivated in alkaline solutions. Electrocardiographic monitoring is recommended during dopamine infusion.
Furosemide administered concurrently with dopamine has been shown to be synergistic in maintaining GFR, RBF and urine flow
in dogs with experimental ARF, and to reduce the severity of some forms of experimental ARF when administered prior to the
renal insult. If oliguria persists despite these measures, dialysis would be the next therapeutic step.
Recently, a selective DA1 agonist (fenoldopam) has become available. Preliminary studies of its renoprotective effects in
people have been promising. One experimental study in healthy cats found that an infusion of 0.5 mcg/kg per minute produced
diuresis in a delayed manner. However, a study in experimental dogs undergoing nephrotomy showed no difference in GFR or urine
volume between dogs receiving fenoldopam or saline. No clinical studies have been reported in dogs or cats with ARF, and its
role in management of oliguric ARF is not yet known.
Dr. Hoskins is owner of DocuTech Services. He is a diplomate of the American College of Veterinary Internal Medicine with
specialities in small-animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200 or e-mail: