A physiological approach to fluid and electrolyte therapy in the horse.

In this article a physiological approach to fluid therapy is discussed, commencing with examination of fluid distribution in the normal horse. The functions of individual plasma electrolyte concentrations are considered and practical causes of acid-base disturbances discussed. When fluid administration is necessary, selection of the route for fluid administration as well as the type of fluid are important considerations and these must be adjusted to the needs of the individual case. Balanced polyionic solutions appear to be most suitable for general use because normal saline can produce hypokalaemia and metabolic acidosis. The use of bicarbonate is indicated mainly where there has been alkali loss (eg, diarrhoea) or severe acidosis associated with increased lactate production. Plasma volume expanders, such as dextran or gelatin polymers, can be considered where a rapid and prolonged restoration of blood volume is required. Fluids should be warmed to body temperature before administration and flow rates up to 6 to 8 litres/h may be safely used. A plan for fluid therapy involves the estimation of existing fluids, as an average horse will require almost 84,000 kJ continuing losses should be estimated and corrected. Maintenance of calorific requirements is difficult using intravenous fluids, as an average horse will require almost 84,000 kJ (20,000 kcal) per day. Lipid emulsions provide up to 8370 kJ/litre but their expense precludes the use of large volumes.