Page 457 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Fluid and Electrolyte Disturbances In Gastrointestinal and Pancreatic Disease 445

chronic illness (i.e., due to endogenous hypercor- a decrease in potassium concentration, and the electrolyte
tisolemia) because these situations may lead to type B composition of the stool approaches that of plasma. 38
hyperlactatemia that does not require aggressive treat- In cases of diarrhea, there is a linear relationship between
ment as does hyperlactatemia caused by hypoperfusion fluid and sodium loss. 38 In human patients,
(type A hyperlactatemia). measurements of fecal electrolyte concentrations and
Hypoadrenocorticism should be ruled out whenever osmolality are used to calculate an osmolality gap, which
hyperkalemia and hyponatremia are present, but up to aids in the differentiation of osmotic and secretory diar-
26% of dogs with hypoadrenocorticism may have normal rhea. The osmolality, sodium concentration, and potas-
þ
þ
mineralocorticoid function and normal Na /K ratios. 68 sium concentration of feces from four normal cats were
Therefore a history of intermittent signs of gastrointesti- reported as 622 to 927 mOsm/kg, 27 to 57 mEq/L,
nal disease may warrant an adrenocorticotropic hormone and 19 to 46 mEq/L, respectively. 42 Stool normally
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stimulation test despite a normal Na /K ratio. Clinico- contains high concentrations of potassium, and fecal
þ
pathologic findings in dogs with primary gastrointestinal potassium loss can become severe in protracted diarrheal
disease may mimic those of hypoadrenocorticism with states. 38 Stimulation of the renin-aldosterone axis as a
Na /K þ ratios less than 27:1 and metabolic acido- result of volume depletion has been suggested as one
þ
sis. 30,73,74 Gastrointestinal diseases reported to mimic potential cause of potassium loss. 82
primary hypoadrenocorticism include trichuriasis, ancy- Dogs with gastrin-secreting tumors may be presented
lostomiasis, salmonellosis, and perforated duodenal ulcer. for evaluation of intermittent or profuse watery diarrhea,
Postulated mechanisms of these electrolyte derangements vomiting, and weight loss. In this setting, diarrhea and
include metabolic acidosis secondary to volume depletion vomiting are probably a result of the increased volume
and fecal loss of bicarbonate with subsequent transloca- and acidity of gastric secretions, which cause gastrointes-
tion of potassium from intracellular to extracellular fluid. tinal ulceration and destruction of pancreatic enzymes. 115
Selective aldosterone deficiency does not appear to be The high concentrations of gastrin may also adversely
responsible for hyperkalemia and hyponatremia in dogs affect intestinal function.
with trichuriasis that have laboratory abnormalities that In humans, profuse watery intermittent or fulminant
mimic those of hypoadrenocorticism. 41 Hypocalcemia diarrhea can be caused by tumors secreting VIP
and hypomagnesemia occur uncommonly in veterinary (VIPomas). 65 The majority of these tumors are located
patients with diarrhea and are most often encountered in the pancreas, although the VIPoma syndrome has been
in animals with protein-losing enteropathy. Ionized associated with tumors at a number of other sites in
hypocalcemia and hypomagnesemia have been described humans. Additional findings include severe hypokalemia,
in Yorkshire terriers with diarrhea, abdominal effusion, metabolic acidosis, and occasionally hypochlorhydria.
leukocytosis, neutrophilia, hypoproteinemia, The profound secretory diarrhea results from the stimu-
hypoalbuminemia, hypocholesterolemia, and increased latory action of VIP on intestinal secretion. The VIPoma
serum activity of aspartate aminotransferase. The hypo- syndrome differs from gastrinoma in that patients
magnesemia and hypocalcemia potentially were the result with VIPoma have normal serum gastrin concentrations
of intestinal loss, malabsorption, and abnormalities of and lack gastric acid hypersecretion and secondary
vitamin D and parathyroid hormone metabolism. 59 upper GIT ulceration. Increased concentrations of VIP
Another two dogs with protein-losing enteropathies were and motilin (VIP, 927 pg/mL; normal range, 0 to
reported to have low ionized calcium, low 25- 84 pg/mL; motilin, 341 pg/mL; normal range, 0 to
hydroxyvitamin D, low 1,25-dihydroxyvitamin D, and 125 pg/ mL) have been documented in a dog with severe
high parathyroid hormone concentrations. These diarrhea and a heart base tumor. The dog had metabolic
abnormalities were thought to be a result of decreased acidosis, hypokalemia, a normal anion gap, and no evi-
76
intestinal absorption of 25-hydroxyvitamin D. Further- dence of renal potassium wasting (Richter and Simpson,
more, ionized hypocalcemia has been noted in critically ill unpublished observations).
dogs admitted to intensive care units and these dogs were
predicted to have longer intensive care and hospitaliza- MANAGEMENT OF
tion. 52 These dogs had a wide variety of gastrointestinal DISORDERS OF THE
diseases (e.g., gastric dilatation-volvulus [5], septic peri- GASTROINTESTINAL TRACT
tonitis [2], gastrointestinal perforation [2], hemorrhagic
gastroenteritis [1], gastrointestinal granuloma [1],
gastrointestinal ulceration [1], and esophageal foreign OVERVIEW OF FLUID THERAPY FOR
body [1]). 52 VOMITING AND DIARRHEA
Normal stool water contains a higher concentration of Correction of volume, electrolyte, and acid-base
potassium than sodium. 38 As stool volumes increase in disturbances is an essential part of the management of
human patients with diarrhea, there is a progressive patients with vomiting and diarrhea. The most appropri-
increase in the sodium and chloride concentrations and ate type, route, and rate of fluid replacement are chosen