South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
With more severe dehydration (7-15%), enteral fluids must be administered with caution because
absorption may be compromised due to decreased blood flow to the intestinal tract. Thus, more
severely dehydrated horses are usually initially treated with intravenous fluids although
administration of enteral fluids and electrolytes in the form of oral pastes are often useful
components of the fluid therapy plan that can decrease the volume of intravenous fluids used.
With a standard intravenous catheter (14 gauge, 13 cm in length) placed in the jugular vein,
intravenous fluids can be administered at a rate of 5-7 litres/hour, depending on the height at
which fluid bags are hung. Rarely is more than one intravenous catheter required for initial
rehydration unless multiple types of products (e.g., crystalloid solutions and whole blood or
plasma) are being administered simultaneously. Further, placement of catheters in both jugular
veins should be approached with caution at initial presentation because venous thrombosis can be
a significant complication in critically ill patients.
Type of fluid: Although water is the most abundant component of most fluid therapy solutions
administered intravenously or via a nasogastric tube, these solutions also contain electrolytes
and/or nutrients (glucose). The most important electrolytes to consider are Na+, K+, chloride (Cl-),
and Ca ++. As illustrated in Figure 1, Na+, K+, and Cl- are quantitatively of greatest importance.
The latter ion, Cl-, is the major exchangeable anion and typically follows losses of the major
cations, Na+ and K+.
As mentioned above, essentially all commercially available crystalloid fluids have an electrolyte
composition similar to plasma. Thus, they are rehydration fluids designed to replace acute losses
of fluid from the ECF. As a result, most of these solutions are appropriate choices for initial
treatment of dehydrated horses and variation in products used between hospitals often reflects
different costs and availabilities, rather than a physiological preferable solution. Two further
comments about initial rehydration of neonatal foals are warranted. First, most sick foals are not
nursing well and have limited energy reserves. Thus, addition of glucose (5-10% dextrose
solution) is recommended for initial rehydration of foals less than 30 days of age. A 5% dextrose
solution can be made by adding 100 mL of 50% dextrose per litre of crystalloid fluid. Second,
foals with uroperitoneum from a ruptured bladder or ureter may have significant hyperkalaemia
and K+ free solutions (e.g., 0.9% NaCl, also with 5% dextrose added) are most appropriate for
treatment of affected foals.
Developing a fluid therapy plan:
Initial rehydration plan: Once hydration status has been assessed, a fluid therapy plan can be
developed. Initially, plans are made for 12-24 hours and subsequently modified after assessing the
patient‟s response to treatment. The volume of fluid administered should include: i) amount
estimated to correct dehydration; ii) amount needed for maintenance; and iii) amount to replace
estimated ongoing fluid losses. As well as being rather variable, the latter is also the most difficult
to predict and is of greatest importance in horses with significant ongoing losses in gastric reflux
or diarrhoea. As an example, assume you are presented with a 500 kg horse afflicted with colitis.
The horse has had diarrhoea for 2 days, is off feed, and clinical examination findings result in an
estimate of moderate (7%) dehydration.
A plan for the initial 12 hours would be formulated as follows:
i.
Rehydration needs:
0.07 (estimated 7% dehydration) x 500 kg = 35 kg = 35 litres
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