South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
Determining when and what type of fluid therapy is needed:
Assessment of hydration status: To determine whether or not a sick horse needs fluid therapy,
hydration status must first be assessed and an estimate of dehydration made. Unfortunately,
clinical examination findings do not become abnormal until a horse becomes 3-5% dehydrated,
with the percent value referring to percentage decrement in body mass due to fluid loss. For
example, an estimate of 3-5% dehydration would lead to an estimated 15-25 litre fluid deficit in a
500 kg horse. Abnormal clinical findings supporting dehydration may include tacky oral
membranes; a cool nose, ears, and extremities; poor distensibility of jugular veins (noticed when
collecting blood samples or inserting a catheter); and delayed recovery of tented skin. In the
author‟s experience, noting the temperature of the nose, ears, and extremities is one of the more
useful indicators of hydration status, especially in neonates (e.g., whether the limbs are cool from
the fetlocks down or from the carpi and tarsi down). The most severely dehydrated horses rarely
have a fluid deficit greater than 15% (75 liter fluid deficit in a 500 kg horse) and dehydration is
estimated between 5-15% on the basis of severity of changes in clinical parameters of hydration
status. In addition to examination findings, these also include packed cell volume (PCV) and
plasma total solids (TS, measured with a refractometer). However, they must always be
interpreted in combination with examination findings because markedly dehydrated horses may
have laboratory data altered by disease (e.g., despite severe dehydration, TS may actually be
decreased in horses with profuse diarrhoea as a result of protein loss in faeces).
As a rule of thumb, all horses that show clinical evidence of dehydration are candidates to receive
fluid therapy. In addition, horses that show marginal evidence of dehydration would likely also
benefit from an initial period of fluid therapy if they are azotemic (increased serum concentrations
of urea nitrogen and creatinine) at admission or have a history of use of nephrotoxic medications
(e.g., non-steroidal anti-inflammatory drugs or gentamicin) for several days.
Route of administration: With development of 5 litre intravenous fluid bags and systems designed
to hang multiple bags (e.g., 20 litres at a time), use of intravenous fluids in equine practice has
expanded considerably over the past 10-20 years. Accompanying this advance in treatment
capability, a consequence appears to have been a decrease in the use of enteral fluid therapy (i.e.,
fluids administered by a nasogastric tube). This is somewhat unfortunate because enteral fluids
are rapidly absorbed across the stomach wall and in the upper small intestine, as long as that
portion of bowel remains functional. In fact, a larger volume of fluids can often be given via this
route (e.g., 8 litres every 30-60 minutes via an indwelling nasogastric tube) than can be
administered through a single intravenous catheter. Recent work supports that the enteral route
may have an additional benefit - specifically, stimulation of intestinal motility. This would be an
advantage in a horse with impaction colic, but it may occasionally be accompanied by
exacerbation of colic signs during the 10-15 minute period after fluid administration. The only
real contraindications for use of enteral fluids are presence of gastric reflux when a stomach tube
is passed or severe resistance by the horse when the tube is being passed. Further, enteral fluid
solutions can easily be made when needed (e.g., 30 g of salt, either iodized or non-iodized, or lite
salt [a 1:1 mix of NaCl and KCl] added to each gallon of water) and are inexpensive. For further
convenience, pre-measured amounts of salt or lite salt can be prepared by pharmacy staff or a
permanent marker can be used to draw a line on a plastic container (e.g., a 60 mL syringe case or
a urine specimen cup) that can be used for stall-side measurement of the appropriate amount of
electrolytes to administer. All in all, enteral fluids are ideal for horses with mild to moderate
dehydration (5-7%) as long as the intestinal tract is healthy enough to absorb the fluids
administered (usually determined by checking for gastric reflux before administration of enteral
fluids).
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