Page 288 - Problem-Based Feline Medicine

280 PART 5 CAT WITH ACUTE ILLNESS

(e.g. therapy with a diuretic). In acute renal Other variable serum biochemistry abnormalities
failure, urine is usually isosthenuric or mini- include hyperglycemia, hyperkalemia, hyponatremia,
mally concentrated. Some cats with chronic hypocalcemia and decreased bicarbonate (total CO ).
2
renal failure maintain adequate urine concentrat-
Other variable urinalysis findings include glucosuria,
ing ability, but this does not appear to happen in
proteinuria, tubular casts, crystaluria, pyuria and bac-
acute renal failure.
teruria.
– If urine specific gravity was not measured prior
to initiating fluid therapy, monitoring serum bio- Diagnostic imaging of the kidneys, urinalysis, urine
chemistry abnormalities will help in distinguish- culture and kidney biopsy may be needed to rule in and
ing pre-renal from renal azotemia. If azotemia is rule out causes of renal failure. See Ethylene glycol
pre-renal in origin, it will normalize within poisoning and Lily poisoning, below.
24–48 hours upon rehydration and/or correc- ● Renal biopsy may also help determine the severity
tion of hypotension, whereas renal azotemia will and reversibility of the injury, but there is poor
remain elevated during this period (although it correlation between histopathologic findings and
may improve). renal function.
– In animals with pre-renal azotemia, urine pro-
duction will increase as the animal becomes
rehydrated and/or hypotension is corrected. The
Differential diagnosis
volume of urine produced and time to do so will
depend on the rate of fluids. Because these ani- Pre-renal azotemia and reduced urine production.
mals are usually acutely dehydrated, rehydration Causes of acute depression, anorexia, dehydration and
is typically performed quickly, so within a few vomiting may cause pre-renal azotemia and reduced
hours urine production is expected. A method to urine production. These causes include acute gastritis,
rapidly detect oliguria or anuria is to give gastroenteritis and pancreatitis. In acute renal failure,
a 10 ml/kg bolus of intravenous fluids over 10 urine will be isosthenuric to minimally concentrated,
minutes. This should cause sufficient volume while in the other disorders urine should be well-
expansion and increase in blood pressure to ini- concentrated, unless there is pre-existing chronic
tiate urine production within 10–30 minutes. If renal failure. Azotemia is more severe in acute renal
there is no urine produced after 30 minutes, failure and will not normalize with rehydration. Acute
another fluid bolus may be considered. If there renal failure may be a complication of a primary dis-
is no urine production after two fluid boluses, order, due to the progression from pre-renal to renal
then it is likely that intrinsic oliguric renal fail- azotemia.
ure is present. Ideally blood pressure should be
Pre-renal azotemia and increased urine production.
measured to confirm that reduced urine produc-
● Both acute renal failure and diabetic ketoacidosis
tion is not due to persistent hypotension that is
may cause acute depression, polyuria, vomiting,
still causing pre-renal azotemia. A normotensive
dehydration, hyperglycemia and glucosuria, and
cat receiving maintenance fluid therapy should
both may be preceded by a history of chronic
produce urine at 0.5–2 ml/kg/h.
polyuria and polydipsia (due to chronic renal failure
– The diagnosis of acute oliguric/anuric renal fail-
and diabetes mellitus, respectively). Diabetic
ure is usually straightforward. Acute non-oliguric
ketoacidosis is confirmed by detecting ketones in
renal failure is more difficult to distinguish from
the blood or urine. Acute renal failure is also an
subacute chronic renal failure and acute-on-
uncommon complication of diabetic ketoacidosis.
chronic renal failure.
Cats with diabetic ketoacidosis may have concur-
A hemogram typically reveals hemoconcentration and rent chronic renal failure.
a stress leukogram. Cats with acute-on-chronic renal ● Other disorders that cause polyuria and polydipsia
failure may have anemia, and this finding is highly in the cat include hyperthyroidism (common), and
suggestive of pre-existing chronic renal failure. The hepatic encephalopathy and central diabetes
anemia may not be evident until the cat is rehydrated. insipidus (rare) (see The Cat With Polyuria and