Page 497 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Fluid, Electrolyte, and Acid-Base Disturbances in Liver Disease 485

Transient repopulation of the gut with beneficial (22 mg/kg orally every 8 to 12 hours), or neomycin
(i.e., non–urease-producing) microorganisms (e.g., (22 mg/kg orally every 12 hours) to decrease enteric pro-
lactobacilli) may provide short-term benefits. Collec- duction of NH 3 from urea and other nitrogenous
tively, these efforts often ameliorate clinical signs of substrates. Caution should be exercised when using neo-
HE. In neurologically impaired patients that cannot tol- mycin because it potentially can be absorbed from the
erate oral medications, cleansing enemas are used to rid intestinal tract to an extent sufficient to result in ototox-
the colon of retained toxins and debris and are followed icity or nephrotoxicity, especially if coexisting inflamma-
by retention enemas (see Table 19-4). Retention enemas tory bowel disease increases its absorption. Rarely,
contain enteric-modulating medications with effects sim- concurrent administration of an antimicrobial may
ilar to those described for oral administration. Simulta- reduce the efficacy of lactulose by decreasing its bacterial
neous oral and per-rectal dosing should be avoided to fermentation. This effect can be detected by checking fecal
prevent diarrhea, cramping, and potential drug overdose. pH, which should be less than 6.0 if effective lactulose
Fermentable carbohydrates Dietary management fermentation has occurred. Transient repopulation of
of HE optimally is combined with oral administration the intestine with non–urease-producing microorganisms
of a fermentable carbohydrate such as lactulose (e.g., lactobacilli)may provide only short-term benefit but
(b-galactosidofructose, most commonly used), lactitol carries little risk. Products that deliver lactobacilli or
(b-galactosidosorbitol), or lactose (in lactase-deficient similar probiotic organisms also provide fermentable
patients) because this strategy increases patient nitrogen carbohydrate substrates, which may explain their
tolerance. Lactulose and lactitol are synthetic benefits. Rarely, hepatic or systemic infections with the
disaccharides not digested by mammalian enzymes. Lac- probiotic organism have been encountered.
tose may achieve a similar effect in lactase-deficient Cleansing and retention enemas Conventional
patients and is much cheaper. These compounds undergo measures that decrease systemic NH 3 concentrations
bacterial fermentation in the intestinal tract, yielding lac- are directed at cleansing and removing noxious substrates
tic, acetic, and formic acids, which acidify the enteric from the colon and modifying the enteric environment.
lumen (pH <5.0). These organic acids constitute an Initially, this approach involves cleansing rectal lavage
osmolal load, provoking a cathartic influence (softening using warm isotonic fluids and removal of residual
feces and increasing the frequency of defecation). This ingesta, nitrogen-containing compounds, urease-pro-
cathartic effect increases the gastrointestinal transit rate, ducing microorganisms, and encephalopathic toxins.
which commonly is slow in patients with HE and portal Next, a retention enema containing an antimicrobial,
hypertension. The acidic luminal pH suppresses bacterial a fermentable carbohydrate, an acidifying solution, or
urease activity, renders the enteric environment inhospi- activated charcoal is instilled. Use of a fermentable carbo-
table for many ammonia-generating organisms, and traps hydrate is preferred because it reduces enteric pH and
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NH 3 as the NH 4 , thereby increasing its elimination in traps NH 3 , and eliminates it as NH 4 .
feces. Carbohydrate fermentation also increases microbial FLUID THERAPY IN LIVER DISEASE
incorporation of nitrogen, thereby decreasing the nitro-
gen available for systemic absorption. Fecal nitrogen General Considerations
excretion increases up to fourfold because of increased Selection of the most appropriate fluid for patients with
fecal volume and nitrogen trapping. Carbohydrate fer- hepatobiliary disease must take into consideration their
mentation also decreases formation of potentially toxic propensity for third-space fluid accumulation (e.g.,
short-chain fatty acids (e.g., propionate, butyrate, valer- edema, ascites), hypoalbuminemia, hyponatremia, hypo-
ate) thought to contribute to HE. The dose of ferment- kalemia, coagulopathies, and hyperlactatemia and
able carbohydrate administered must be individually whether preexisting acid-base disturbances put them at
titrated to achieve several soft stools each day. Too much risk for HE. In patients without evidence of synthetic fail-
lactulose induces abdominal cramping (because of fer- ure or HE, balanced polyionic solutions are appropriate
mentation and gas production), stimulates peristalsis and should be supplemented with KCl as routinely
(causing borborygmus), and causes watery diarrhea. recommended for maintenance needs.
Generation of organic acids from lactulose rarely can When ascites or edema precedes fluid administration
result in metabolic acidosis, dehydration, and or develops after infusion of polyionic solutions, fluid
hypernatremia. 155 Lactulose may be contraindicated in support must be modified to reduce the administered
patients with hypercalcemia if increased absorption of cal- load of sodium. Ascites has been experimentally induced
cium from the gut exacerbates hypercalcemia. 189 in medium-sized dogs with cirrhosis by ingestion of only
Given together, lactulose and an enteric antimicrobial 85 mEq of sodium per day. Considering that a 15-kg dog
synergistically improve nitrogen tolerance in most has a maintenance volume requirement of approximately
animals. Lactulose (0.25 to 1 mL/kg orally every 8 to 1 L/day, the sodium content of commonly used
12 hours) commonly is combined with metronidazole polyionic crystalloid solutions may promote ascites for-
(7.5 mg/kg orally every 8 to 12 hours), amoxicillin mation when maintenance volumes are administered.