Fluid Therapy in the Field Kevin Corley BVM&S PhD DECEIM DACVIM DACVECC MRCVS Specialist, Anglesey Lodge Equine Hospital, The Curragh, Co Kildare, Ireland Director, equineadvances.com Fluid therapy Fluid therapy is a potentially life-saving treatment that, with some preparation, can be easily applied in the field. Many common conditions of horses can result in the need for fluidtherapy. Examples include colic, diarrhoea and exhausted horse syndrome. Starting fluid therapy early, especially in diarrhoea and in foals, can make a great difference both to the eventual survival of the horse and to reducing the final cost to the owner. Hypovolaemia and dehydration Even though they may coexist in the same horse, hypovolaemia and dehydration are important to distinguish, because their therapy is different. Hypovolaemia requires emergency intravenous treatment to rapidly restore circulating volume. There is considerable evidence linking markers of hypovolaemia on hospital admission with morbidity and decreased survival in equine colic and neonatal foals. Dehydration may be treated over a more prolonged period, and may be corrected with intravenous, nasogastric, or occasionally free-choice oral fluid therapy. Hypovolaemia is defined as a decrease in circulating blood volume. The classic example of hypovolaemia is acute arterial haemorrhage, in which the circulating volume is decreased without a change in the remainder of the extra-cellular fluid volume. Dehydration is defined as a loss of interstitial fluid without a change in the circulating volume. The classic example is moderate sweating during exercise or high ambient temperatures. There are powerful physiological mechanisms protecting the circulating volume during dehydration at the expense of extra-vascular fluid, and it is only with severe dehydration that animals will also become hypovolaemic. Clinical signs of hypovolaemia and dehydration in the adult horse are given below. Clinical Signs of hypovolemia and dehydration in the horse Hypovolaemia Tachycardia Decreased pulse pressure Reduced jugular fill Tachypnoea Cold extremities Decreased urine output Dehydration Tacky mucous membranes Prolonged skin tent Sunken eyes 1
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