Page 287 - Problem-Based Feline Medicine

16 – THE CAT WITH ACUTE DEPRESSION, ANOREXIA OR DEHYDRATION 279

ant dysregulation of water, acid–base and electrolyte ● Intratubular obstruction from desquamated tubular
balance, and accumulation of uremic toxins. Acute epithelial cells.
renal failure may be non-oliguric (polyuric), oliguric or ● Tubular backleak, where filtrate leaks across the
anuric. injured tubular epithelium and is thus shunted
● Oliguria is defined as < 0.27 ml/kg/h, and anuria directly to the peritubular capillaries.
< 0.08 ml/kg/h and these definitions may be used ● Reduced glomerular permeability.
as guidelines for cats.
The central pathophysiologic event in acute renal fail- Clinical signs
ure is acute tubular necrosis. This is initiated by
The salient historical findings are acute depression
altered hemodynamics (ischemia), nephrotoxins or
and anorexia, which are progressive in nature. Most
miscellaneous primary renal diseases. In some cases
cats will vomit; diarrhea may also occur.
more than one mechanism is involved.
● Ischemia may be caused by hypotension (e.g. Physical examination findings are variable.
prolonged anesthesia, shock), thromboembolism Hypothermia typically develops within 24–48 hours
(e.g. cardiomyopathy), or acute hydronephrosis of the development of oliguria or anuria. Bradycardia
(e.g. prolonged urethral obstruction). may be present.
– Hemodynamically mediated acute renal failure ● Body condition is normal in a cat without pre-exist-
may be caused by the same factors that cause ing chronic renal failure or other disorder-promot-
pre-renal azotemia, but the reduced perfusion of ing weight loss.
the kidney is so profound that it leads to acute ● Renal size is normal to large in a cat without pre-
tubular necrosis. existing renal disease, and kidneys may be painful
● Nephrotoxins include ethylene glycol and lilies; mer- on palpation. Kidneys are likely to be small in cats
cury, lead and other heavy metals; aminoglycoside with chronic renal failure. Kidneys may also be
antibiotics and amphotericin B; NSAIDs, and enlarged in FIP, lymphoma, polycystic kidney dis-
cholecalciferol (vitamin D ) rodenticides. The ease, chronic hydronephrosis and amyloidosis, but
3
mechanism of NSAID nephrotoxicity is ischemia are not painful. It should be noted that hydration
from vasoconstriction. The chemotherapeutic status and the quantity of peri-renal fat affects renal
agents doxorubicin, epirubicin and carboplatin are size on palpation. Kidneys may feel larger upon
also nephrotoxic, although the clinical importance rehydration.
of this appears to be low. ● The bladder is small with oliguria and anuria,
● Primary renal diseases do not commonly cause may be large with polyuria, and is large and turgid
acute renal failure in the cat. Glomerulonephritis, with urethral obstruction. Owners should be
amyloidosis, feline infectious peritonitis, bacterial queried as to when the cat was last seen to urinate.
pyelonephritis and bilateral renal lymphoma may ● Halitosis and oral ulceration and dehydration are
cause renal failure with a more acute clinical course common findings.
than typical chronic renal failure due to age-related
chronic tubulointerstitial disease, but true acute
Diagnosis
renal failure is rare. It is most likely to occur with
acute bacterial pyelonephritis. Acute exacerbation The diagnosis of acute renal failure is based on:
of chronic renal failure (“acute on chronic renal ● Acute onset of clinical signs.
failure”) may also occur; the mechanism in most ● Elevated serum urea, creatinine and phosphorus
cases is probably ischemia. levels.
● Increased (polyuria), or reduced (oliguria/anuria)
Acute oliguric renal failure is classically divided into
production of inappropriately concentrated
initiation, oliguric, polyuric and recovery stages.
urine.
The oliguric stage is maintained by various factors, – In cats with pre-renal azotemia, urine specific
including: gravity should be > 1.035 unless there is another
● Arteriolar vasoconstriction. mechanism present for reducing specific gravity