Fluid Therapy and Monitoring

Fluid therapy plays a critical role in the therapy of most seriously sick animals and a supportive role in animals undergoing anaesthesia. An ability to understand some basic principles and apply these can make a major improvement in case management. This starts with addressing the hydration status of the patient which then enables decisions to be made such as the type of fluid to be given, the route of administration and the volume needed. Approximately 60% of an adult horse’s bodyweight is water (80% in foals) and this is divided with approximately two-thirds in the intracellular space (ICF) and one-third in the extracellular space (ECF) (Fig 1). The effective circulating volume is the ECF that is in the vascular space and effectively perfusing tissues. This varies directly with the ECF volume and the total body sodium (the primary solute holding the water in the ECF). Oncotic pressure is also important as plasma proteins, specifically albumin, hold the water within the vasculature.

Water loss can be divided into sensible losses, such as from the urinary and gastrointestinal tract and insensible losses, such as respiration and sweating. Normal ongoing losses for a resting adult horse are 55–65 ml/kg bwt/day, or about 25 l for a 500 kg horse. [...]