Page 425 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Perioperative Management of Fluid Therapy 415

synthesizes many proteins, and hypoalbuminemia and correct all of the preceding abnormalities except the
deficiencies of clotting factors may occur as hepatic insuf- hypoglycemia and metabolic acidosis, which should be
ficiency progresses. These alterations are managed as monitored during therapy and corrected as necessary
described earlier. Blood ammonia concentrations are by administration of glucose and sodium bicarbonate.
increased in patients with portosystemic shunts and in Hypotension can be especially difficult to manage in these
those with hepatic failure. Consequently, it is important patients intraoperatively, and steroid replacement should
not to administer additional ammonia by the use of stored be started before induction of anesthesia.
blood products that may have increased ammonia
content. DIABETES MELLITUS
In controlled diabetes, there rarely is any major concern
ENDOCRINE DISEASE about fluid balance preoperatively. The animal’s normal
feeding regimen and insulin dose are used on the day
before surgery. On the morning of surgery, the animal
DIABETES INSIPIDUS receives one third to one half of its daily dose of insulin,
Animals with diabetes insipidus must be monitored care- and blood glucose concentration is monitored through-
fully during the preoperative period to be sure they con- out the procedure. 106 The animal is treated with glucose,
tinue to drink water. The owner should be asked how insulin, or some combination of these as determined by
much water the animal is consuming to ensure that a sim- serial blood glucose measurements. Animals with uncon-
ilar volume can be administered intraoperatively. Animals trolled diabetes may be dehydrated and may require fluid
with complete central diabetes insipidus can become therapy before anesthesia.
markedly dehydrated within a matter of hours (5% dehy-
dration may occur after 4 hours of water deprivation). HYPOTHYROIDISM
Consequently, affected animals should have access to Patients with hypothyroidism rarely have any electrolyte
water until the time of premedication, and intraoperative disturbances but can be hypotensive and have a poor
management should take into account the actual urine response to positive inotropes and vasoconstrictors.
production of that animal so it is best to place a urinary If possible, the animal should be adequately treated for
catheter and use a closed collection system to monitor hypothyroidism for at least 1 to 2 weeks before it is
urine volumes. anesthetized.
HYPERADRENOCORTICISM HYPERTHYROIDISM
Animals with hyperadrenocorticism are polyuric and Animals with hyperthyroidism tend to be in a
polydypsic and should have access to water until the time hyperdynamic state and are at risk for fatal, catechol-
of premedication. Some dogs with hyperadrenocorticism amine-mediated arrhythmias when anesthetized. It is best
have mildly increased serum sodium and mildly decreased if the animal is treated with methimazole for at least
serum potassium concentrations, but these rarely are of 2 weeks before anesthesia. 140
sufficient magnitude to be of concern. Animals with
hyperadrenocorticism tend to be hypertensive, which ACCESS TO THE
may exacerbate underlying cardiac disease (e.g., mitral CIRCULATION
regurgitation), and they may have increased sensitivity
to vasoconstrictive drugs. They also bruise easily, and spe- The technical aspects of fluid administration are covered
cial care should be taken when placing intravenous in Chapter 15. In the perioperative period, access to the
catheters. If the affected animal is being anesthetized circulation via the intravenous or intraosseous route
for major surgery, hypercoagulability and increased risk should be available so that fluids can be given rapidly
of pulmonary thromboembolism are concerns. Prophy- should the need arise. As discussed earlier, the diameter
lactic therapies for hypercoagulability may include the of the catheter should be sufficient to allow fluids to be
use of regular or low molecular weight heparins, plasma, administered rapidly enough for the expected deficits.
and HES. It also is important that the connections to the animal
be set up carefully and that they are secure. If the fluid line
HYPOADRENOCORTICISM becomes disconnected with the animal draped for sur-
Hyponatremia, hypochloremia, hyperkalemia, gery, it may not be detected quickly, and the animal
hypovolemia, hypoglycemia, metabolic acidosis, and azo- may experience substantial blood loss from the catheter.
temia commonly are associated with hypoadreno- When the patient is prepared for a surgical procedure,
corticism. These abnormalities are associated with the anesthetist should make sure to set up the fluid lines
hypotension and decreased sensitivity to positive so that an injection port is accessible without the need to
inotropes and vasoconstrictive drugs. The fluid of choice reach under the drapes. The animal also should be posi-
for managing these animals is 0.9% NaCl, which tends to tioned in such a way that the fluids can flow easily. Drugs