Page 636 - Small Animal Internal Medicine, 6th Edition

608 PART IV Hepatobiliary and Exocrine Pancreatic Disorders

underlying cause are the most important approaches, but although neomycin is more useful for acute HE rather than
guidelines have changed over the last few years with respect long-term use because intestinal bacteria tend to become
VetBooks.ir to protein restriction, and it is now clear that many dogs with resistant to neomycin. In addition, it is not systemically
absorbed and remains in the GI tract, which will not help
congenital or acquired PSS have higher protein requirements
than do normal animals. Long-term feeding of a protein-
Other therapeutic strategies investigated in humans with
restricted diet is contraindicated and will result in protein- any systemic infection.
calorie malnutrition. The emphasis has shifted to feeding a chronic HE include ornithine aspartate supplementation
digestible protein in small amounts and often to reduce the (see Box 36.6) and probiotics to increase the numbers of
work of the small intestine and thus glutamine metabolism. beneficial bacteria. These may show benefit in dogs in the
There is preliminary evidence that soybean or dairy protein future, but there are currently no published studies docu-
may be preferable to other protein sources. menting their use in small animals.
Most, if not all, dogs with congenital or acquired PSS can Certain conditions are known to accentuate or precipitate
tolerate normal protein concentrations if other measures are HE and should be avoided or treated aggressively when
also implemented, as outlined later and in Box 36.6. A few detected (see Box 33.2). In many cases it is the precipitating
require more marked restriction in the short term, but every factors, rather than the diet, that are most important in trig-
effort should be made to increase to a normal protein con- gering HE. It is particularly important to identify and treat
centration over the long term. The body condition score and any concurrent inflammatory disease that can trigger HE
serum protein concentrations should be carefully monitored episodes in susceptible animals.
to avoid negative nitrogen balance.
Lactulose (β-galactosidofructose) is a semisynthetic Management of Acute Hepatic
disaccharide that is not digestible by mammals and therefore Encephalopathy
passes into the colon, where it is degraded by bacteria into Acute HE is a true medical emergency. Fortunately, it is much
short-chain fatty acids (SCFAs), particularly lactic and acetic less common than chronic waxing and waning HE. Animals
acid. These SCFAs help control signs of HE by acidifying the may present in status epilepticus or comatose, and although
intestinal contents, which traps ammonium ions in the colon, HE initially causes no permanent brain damage, prolonged
and by promoting osmotic diarrhea. In addition, SCFAs are seizures, status epilepticus, or coma will; prolonged severe
used as an energy source by colonic bacteria, allowing them HE by itself may lead to serious cerebral edema as a result
to grow and thus incorporate colonic ammonia into their of accumulation of the osmolyte glutamine (from ammonia
own bacterial protein, which is subsequently lost with the detoxification) in astrocytes. In addition, the systemic effects
bacteria in the feces (a type of bacterial ammonia trap). of acute HE, particularly hypoglycemia, can be fatal if not
The dose is adjusted until there are two to three soft recognized and treated. The treatment of acute encephalo-
stools per day (see Box 36.6); overdosing results in watery pathic crises is outlined in Box 36.7. Intensive management
diarrhea. There are no known complications of chronic is required. However, treatment is worthwhile because some
lactulose use in animals other than diarrhea. However, the animals can go on to complete recovery and successful long-
efficacy of lactulose has never been critically evaluated in term medical management, particularly if the acute crisis
dogs and cats with HE. Recent studies in humans have been was triggered by a definable event (e.g., acute GI bleeding in
contradictory with one meta-analysis suggesting no benefit, a dog with chronic liver disease and portal hypertension).
but a more recent meta-analysis suggested some benefit in Nothing by mouth (NPO), administration of enemas, and IV
HE. Lactulose can also be given by enema in animals with fluid therapy constitute the basic therapeutic approach. Warm
acute HE (see Box 36.7). Many dogs object strongly to the water cleansing enemas may be useful simply by removing
sweet taste of lactulose; an attractive alternative is lactitol colonic contents and preventing absorption of intestinal
(β-galactosidosorbitol), which is related to lactulose and can encephalotoxins. Lactulose or dilute vinegar may be added
be used as a powder (500 mg/kg/day in three to four doses, to acidify the colon and decrease absorption of ammonia.
adjusted to produce two to three soft stools daily). Currently, The most effective enema contains three parts lactulose to
lactitol is available in the United States as a food sweetener seven parts water at a total dose of 20 mL/kg. The solution
but has not been studied in dogs with HE. is left in place, with the aid of a Foley catheter, as a retention
If dietary therapy alone or in combination with lactulose enema for 15 to 20 minutes. For lactulose to be beneficial, the
is insufficient to control signs of HE, antibiotics may be pH of the evacuated colon contents must be 6 or lower. These
added. Usually, amoxicillin is used at 22 mg/kg PO q12h. enemas can be given every 4 to 6 hours. Because lactulose is
Traditionally, antibiotic therapy was believed to work simply osmotically active, dehydration can occur if enemas are used
by reducing colonic bacterial metabolism. However, recent too aggressively without careful attention to fluid intake.
studies implicating inflammatory mediators in triggering Fluids chosen for the replacement of losses, volume expan-
HE provide an alternative explanation for the efficacy of sion, and maintenance should not contain lactate, which is
antibiotics in some animals with HE where they may also be converted to bicarbonate, because alkalinizing solutions may
treating undetected urinary tract or other infections. Anti- precipitate or worsen HE by promoting the formation of
biotics effective for gram-negative, urea-splitting organisms the more readily diffusible form of ammonia. Half-strength
(neomycin sulfate, 20 mg/kg PO q12h) may also be used, (0.45%) saline solution in 2.5% dextrose is a good empirical