South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
ii.
Maintenance needs:
50 mL/kg/24 h x 500 kg = (25,000 mL/24 hours)/2 = 12.5 litres
iii.
Ongoing losses:
Estimated at 2 litres/h x 12 h = 24 litres
iv.
TOTAL:
35 + 12.5 + 24 = 71.5 litres
Thus, ~70 litres of fluid needs to be administered over the initial 12 hours of treatment. This
could be accomplished by hanging 14 - 5 litre bags with an infusion rate of ~6 litres per hour. As
an alternative, a nasogastric tube could be placed and 10 litres of fluid could be administered 7
times over the initial 12 hours. A combination of intravenous fluids and enteral fluids is probably
the most logical approach in this case. Most commonly, however, such horses are treated almost
exclusively with intravenous fluids because most clinicians do not want to repeatedly pass a
nasogastric tube in a sick, depressed horse and prefer not to place an indwelling nasogastric tube
in horses that they are encouraging to eat. From a physiological basis (not to mention a cost
basis), however, enteral fluid therapy alone would be a completely acceptable alternative and this
point should be remembered when treating horses for which owners may not be able to afford
intravenous fluid therapy (especially when the alternative may be euthanasia).
In general, selection of almost any of the commercially available crystalloid polyionic solutions
would be appropriate for initial intravenous rehydration as the most important factor is to
administer an appropriate volume of fluids. Fine-tuning of the fluid therapy plan is usually
performed after initial laboratory data becomes available and after the response to the initial 3-6
hours of treatment is observed. Modifications to the initial plan may include changing the rate of
fluid administration, correction of acid-base disorders, and replacement of specific or anticipated
electrolyte deficits by adding electrolytes to the base fluid or supplementing needed electrolytes in
enteral solutions or as oral pastes.
Additives to the base fluid: At present, limitations of fluid therapy in equine patients are that
commercially available intravenous rehydration solutions fail to address K+ and Ca++ deficits and
maintenance fluid solutions (for use once rehydration has been accomplished) are not available.
Ideal maintenance solutions would contain less Na+ and more K+ and Ca++ than rehydration
solutions and would also partially supply energy needs. Another factor to consider is the nature of
the dehydration being treated. For example, a horse that has become dehydrated over a period of 2
to 4 days (e.g., water deprivation) has a different type of fluid loss than a horse that has developed
acute diarrhoea over the past 12 hours or has been raced under hot humid conditions after
receiving furosemide for prophylaxis against exercise-induced pulmonary haemorrhage. In the
horse deprived of water, fluid deficits have developed more slowly and dehydration involves a
loss of both ECF (Na+ rich fluid) and ICF (K+ rich fluid). In contrast, sweating and furosemide
administration produce more acute losses of fluid that are predominantly from ECF. Thus, the
water deprived horse would have a greater depletion of body K+ stores while the racehorse would
have greater depletion of body Na+ stores.
It is important to emphasize that most horses have adequate body reserves of these electrolytes
and energy to get them through a couple of days of disease. Therefore additives to crystalloid
fluids are not routinely necessary for horses receiving fluid therapy for 12-48 hours for supportive
treatment for impaction 6