Page 460 - Small Animal Internal Medicine, 6th Edition

432 PART III Digestive System Disorders

CHAPTER 28
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General Therapeutic

Principles

FLUID THERAPY checked for unabsorbed fluids before administering more
fluid SC. Severely dehydrated animals often absorb SC fluids
Fluid therapy is primarily used to treat shock, dehydration, very slowly, making initial intravenous (IV) administration
and electrolyte and acid-base disturbances. Accurately pre- preferred. IV fluid administration is required in patients that
dicting electrolyte and acid-base changes on the basis of are severely dehydrated or are in shock, even if a venous
clinical parameters is impossible, hence serum electrolyte cutdown is necessary. Intramedullary administration may be
concentrations typically must be measured in significantly used if an IV catheter cannot be established. To do this, a
ill patients. Vomiting gastric contents classically but incon- large-bore hypodermic needle or a bone marrow aspiration
sistently produces hypokalemic, hypochloremic, metabolic needle (preferable) can be inserted into the femur (trochan-
alkalosis. Loss of intestinal contents classically produces teric fossa), tibia, wing of the ilium, or humerus. Fluids can
hypokalemia with or without acidosis, but hypokalemic met- be administered by the intramedullary route at a mainte-
abolic alkalosis may occur. Vomiting animals are often hypo- nance rate or faster. Intraperitoneal administration repletes
kalemic, but patients with hypoadrenocorticism or severe the intravascular compartment more slowly than IV or intra-
renal failure may be hyperkalemic. Electrolyte concentra- medullary techniques and is not recommended.
tions can quickly be determined by point-of-care methodol- Dogs in hypovolemic shock typically have tachycardia,
ogy. If fluid therapy must be started in a severely ill vomiting poor peripheral perfusion, cool extremities, prolonged capil-
patient before electrolyte concentrations are known, physi- lary refill time, weak femoral pulse, and/or tachypnea, while
ologic saline solution plus 20 mEq potassium chloride per dogs in early systemic inflammatory response syndrome
liter is typically a reasonable choice (Table 28.1), assuming (SIRS) initially have red oral mucous membranes, warm
the fluids are administered at one to two times maintenance extremities, and a strong, bounding femoral pulse before
requirement. If point-care-methodology is unavailable, a classic signs of shock occur. Treatment of severe shock does
lead II electrocardiographic (ECG) tracing may be evalu- not consist of giving a fixed amount of fluids; rather, the
ated to look for evidence of hyperkalemia (see Chapter 53). clinician gives fluids to effect. This often consists of an initial
Reexpanding the vascular compartment and improving IV bolus of 10 to 20 mL/kg of an isotonic crystalloid (e.g.,
peripheral perfusion alleviates lactic acidosis. Hence, bicar- lactated Ringer’s, Normosol R or Physiologic saline, all typi-
bonate administration is almost never needed, and may in cally without supplemental potassium) over 15 to 30 minutes.
fact be detrimental. Bicarbonate is primarily administered to Next, instead of “blindly” giving a fixed, calculated amount,
patients with extreme acidosis (e.g., pH < 7.05 or bicarbonate fluids are administered until the patient is hemodynamically
< 10 mEq/L) that are in imminent danger of dying. Bicar- stable, remembering that it is easy to overhydrate cats. Ulti-
bonate, lactated Ringer’s solution, and Normosol-R should mately, one blood volume (i.e., 90 mL/kg for the dog; 50 mL/
not be used if alkalosis seems likely (e.g., vomiting of gastric kg for the cat) is usually administered over the first 1 to 2
origin). hours. However, additional fluids are typically needed 30 to
Parenteral fluid administration is indicated if the animal 60 minutes later because the initial crystalloids quickly redis-
is significantly hypovolemic or if absorption of enteral fluids tribute into the interstitial compartment. Large dogs in
is questionable (e.g., severe intestinal disease, obstruction, severe shock (e.g., gastric dilation/volvulus) may require two
vomiting, or ileus). Subcutaneous (SC) fluid administration simultaneous 16- to 18-gauge cephalic catheters and IV bags
is acceptable if the animal is not severely dehydrated or in placed in pneumatic compression devices to achieve an ade-
shock, absorbs the fluids, and tolerates repeated SC admin- quate flow rate.
istration. Multiple SC depots of 10 to 50 mL each are given, Hypertonic saline and/or colloids allow small volume
depending on the animal’s size. Dependent areas should be resuscitation, which is easier than administering large

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