South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
than necessary in many horses. Nevertheless, there are a couple of general rules that can be
followed. First, the medical or surgical problem being treated should be stable or improving for
12-24 hours before discontinuation of fluid therapy is considered. This would include correction
of dehydration and at least 6-12 hours of fluid administration at a maintenance rate alone. Fluid
therapy does not necessarily have to be continued until all laboratory data, including serum
electrolyte concentrations and measures of renal function, have returned to the normal ranges.
This is especially true for horses that are improving in response to treatment. Second, when the
medical or surgical disorder has been accompanied by partial or complete anorexia, a reasonable
goal is for the horse to be eating at least 50% of a normal feed ration, preferably with an
increasing appetite, before fluid therapy is discontinued. There are obvious exceptions to this rule;
for example, a horse being treated for impaction colic with enteral fluids (via a nasogastric tube)
will usually not be offered feed until after the last dose of enteral fluids has been given. However,
when intravenous fluids have been employed either exclusively (e.g., because of gastric reflux) or
in conjunction with enteral fluids, intravenous fluids are often continued at a maintenance rate for
12-24 hours after feed is again offered. The main point of this rule is that fluids do not need to be
continued until the patient is back on full feed. Third, a more cautious approach to discontinuing
fluid therapy should be considered in horses receiving multiple potentially nephrotoxic
medications (e.g., gentamicin and flunixin meglumine or phenylbutazone), especially if indices of
renal function are above the normal ranges. In addition, horses continuing on these medications
may benefit from administration of oral electrolyte pastes, mostly NaCl given in an attempt to
stimulate greater voluntary water intake and associated urine output, once enteral or intravenous
fluids have been discontinued.
The decision to discontinue fluid therapy is more difficult in patients with long-standing (>5
days), ongoing fluid losses such as persistent gastric reflux with small intestinal disorders or
persistent diarrhoea with more severe cases of enterocolitis. These types of cases are often
receiving multiple intravenous infusions (e.g., partial or total parenteral nutrition, lidocaine, etc.)
in addition to maintenance fluid support. In fact, when all the fluids being administered are added
up, these patients are often receiving fluid at a rate greater than maintenance needs. Further, they
are often receiving excessive amounts of Na+ and less than adequate amounts of K+. Again,
excess Na+ replacement leads to greater urine output and exacerbates depletion of body K+ stores.
In addition to requiring more frequent assessment of acid-base status and serum electrolyte
concentrations, such patients may be good candidates for using oral electrolyte pastes to correct
replace K+ deficits and provide further Na+ when ongoing losses continue. At the same time, the
approach should be to “challenge” these patients, once they are considered stable, by
discontinuing fluid therapy for 12-24 hours. If their clinical condition deteriorates (e.g., a decrease
in appetite; greater depression; and increases in heart rate, PCV, and TS), fluid therapy can be
started again. In these cases of more serious disease, affected horses may need to be challenged by
having fluid therapy discontinued several times before they can remain stable without this aspect
of supportive care.
References
Carlson GP. Fluid and electrolyte dynamics in the horse. Proc 14th ACVIM Forum, 1986, pp. 7-29 to 7-41.
Schott HC: Fluid therapy: a primer for students, technicians, and veterinarians in equine practice. Vet Clin North Am:
Equine Pract 22:1-14, 2006.jmc
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