Page 458 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

446 FLUID THERAPY

based on the patient’s hydration, tissue perfusion, and The effect of vomiting and diarrhea on acid-base bal-
electrolyte and acid-base status. The presence of anemia ance is difficult to predict, and therapeutic intervention to
or hypoalbuminemia and the potential for continuing correct acid-base imbalance should be based on blood gas
fluid loss through vomiting, diarrhea, fever, and compen- analysis. Patients with normal acid-base status or mild
satory hyperventilation associated with metabolic acidosis metabolic acidosis may be given lactated Ringer’s solu-
must also be taken into account. Minimal evaluation of tion at a rate sufficient to correct fluid deficits and provide
the patient with gastrointestinal disease should include for maintenance and ongoing losses for a 24-hour period.
determination of body temperature, heart rate, skin tur- Potassium depletion may be a consequence of prolonged
gor, capillary refill time, packed cell volume (PCV), total diarrhea, vomiting, or anorexia, but most polyionic
protein concentration, urine specific gravity, and urine replacement fluids contain only small amounts of potas-
pH, as well as serum concentrations of sodium, potas- sium. Consequently, KCl is usually added to parenteral
sium, chloride, total CO 2 , and glucose. Measurement fluids and adjusted based on serum potassium
of blood gases, blood pressure (central venous and concentrations. When severe metabolic acidosis is present
arterial), and urine output is required for optimal care (pH <7.1; HCO 3 <10 mEq/L), sodium bicarbonate
of patients with severe gastrointestinal disease. (1 mEq/kg) can be given. Care should be taken to rule
Oral fluid therapy may be useful for patients with diar- out respiratory acidosis before administering sodium
rhea that can tolerate oral intake. Subcutaneous adminis- bicarbonate and to administer it slowly and in small
tration of an isotonic balanced electrolyte solution may be amounts (0.5 mEq/kg over 15 minutes) to prevent cere-
sufficient to correct mild (5%) fluid deficits but is insuffi- brospinal fluid acidosis, aggravation of hypokalemia, or
cient for patients with moderate (5% to 10%) or severe hypocalcemia. Additional bicarbonate supplementation
(>10%) dehydration. For patients with moderate to is based on repeated blood gas analyses. Metabolic alka-
severe dehydration, inadequate oral intake, electrolyte losis usually responds to correction of the volume, chlo-
imbalance, or signs of hypovolemic or endotoxic shock, ride, and potassium deficits with 0.9% NaCl
intravenous fluid administration is necessary. supplemented with KCl administered intravenously.
The rate of fluid administration depends on the pres- Diagnostic investigations should initially focus on rul-
ence or absence of shock, the extent of dehydration, and ing out upper gastrointestinal obstruction. Administra-
the presence of cardiac or renal disease that may predis- tion of antisecretory drugs (e.g., H 2 antagonists) may
pose the patient to volume overload. Patients with a limit chloride efflux into gastric juice. When acid hyper-
history of vomiting that are mildly dehydrated are usually secretion is present or suspected, it is best managed by
responsive to crystalloids (e.g., lactated Ringer’s solution administration of a proton pump inhibitor (e.g., omepra-
or 9% NaCl) at a rate that provides maintenance needs zole at 0.7 to 1.0 mg/kg every 24 hours). Somatostatin
and replaces existing deficits and ongoing losses over a analogs may also be useful to control gastric acid
24-hour period. Patients with signs of shock require more hypersecretion (e.g., octreotide at 2 to 20 mg/kg subcu-
aggressive support. The volume deficit can be replaced taneously every 8 hours). 115
with crystalloids at an initial rate of 60 (cat) to 90 Other symptomatic treatments considered initially in
(dog) mL/kg/hr, which is then tailored to maintain tis- patients with vomiting and diarrhea are antacids and
sue perfusion and hydration. Central venous pressure antiemetics when vomiting persists. Prophylactic use of
monitoring and evaluation of urine output are necessary antibiotics (e.g., cephalosporins, ampicillin) may be
for patients with severe gastrointestinal disease, especially warranted in animals with shock and suspected gastroin-
those with third-space losses of fluid into the gut or testinal barrier dysfunction. Analgesia can be provided
peritoneum. Colloids and hypertonic solutions can using opioids (e.g., buprenorphine at 10 to 20 mg/kg
also be used to reduce the amount of crystalloid intramuscularly).
required (e.g., 5 mL/kg of 7% NaCl in 6% dextran intra-
venously, 10 to 20 mL/kg/day of degraded gelatin Oral Rehydration Solutions
[Haemaccel] intravenously). Colloids are also useful in The rationale for use of oral rehydration solutions (ORSs)
hypoproteinemic patients. Endotoxic shock is a common is the coupled transport of sodium with glucose or other
complication of severe gastrointestinal disease. Warning actively transported small organic molecules and hence
signs of endotoxemic shock include fever or subnormal the promotion of water absorption. 25,37 These
body temperature, tachycardia, increased respiratory rate, cotransport processes often remain relatively unaffected
slow capillary refill time, hyperemic or pale mucous in acute infectious (e.g., bacterial, viral) cases of diar-
membranes, transient leukopenia followed by leukocyto- rhea. 124 In secretory diarrhea, the epithelium maintains
sis with a left shift and toxic neutrophils, low-normal cen- its absorptive capacity and cotransport processes that
tral venous pressure, and bounding pulses. Patients with are important for the success of oral rehydration ther-
endotoxic shock must be treated aggressively with fluid apy. 124 With certain viral causes of diarrhea (e.g., rotaviral
therapy, broad-spectrum antibiotics, glucocorticoids, infection in children), patchy epithelial damage may allow
oxygen, glucose, and bicarbonate as indicated. 47 oral rehydration to be of benefit. 106,107 A balanced ORS