These should be used in preference to iv fluids where possible. They usually come as a dry powder which is made up with tap water into an isotonic / slightly hypotonic solution just before administration. Constituents vary but usually include:
acetate (1mmol = 1mmol HCO3-)
citrate (1mmol = 3mmol HCO3-)
propionate (1mmol = 1mmol HCO3-)
They may also contain starches to be metabolised for energy (adding extra glucose would increase osmolarity of solution and reduce water uptake) and flavourings. Palatability is a problem in small animals.
Only sugar and salt are strictly necessary, the other components are just to improve efficiency. The WHO has published a recipe for third world children: 3.5g salt, 2.5g sodium bicarbonate, 1.5g potassium chloride and 20g glucose made up to one litre with water. This could be used in animals if necessary, although the bicarbonate will change stomach pH enough to cause problems with milk clotting if both are given together.
mild diarrhoea - especially neonatal animals - cheap enough to use in farm animals
water deprivation
vomiting, severe electrolyte imbalances or shock
They are usually given ad lib in place of drinking water (the animal must be well enough to drink), but if giving by stomach tube, give little and often. The dose depends on the size of the animal's stomach - too much will cause regurgitation ± inhalation pneumonia).
