(less than one litre of fluid is obtained during attempts to evacuate the stomach by refluxing) and examination per rectum does not reveal distended loops of small intestine, it would usually be safe to start the enteral fluids again. Continuous enteral fluids can be easily given via a special kit (Kruuse, Denmark). This kit consists of a narrow gauge stomach tube with an adapted end to directly screw onto a giving set. Fluid and premeasured pouches of electrolytes are added to canisters, and connected to the giving set. The stomach tube is kept in place by a muzzle and Velcro straps. We have used this system on several horses and it appears to work very well. Tubes and delivery systems used for nasogastric administration of fluids need to be clean, but not sterile. However, they should be sterilised after use on a horse with a known or suspected infectious agent, including those with anterior enteritis. Types of fluid for enteral fluid therapy It is possible to treat moderately dehydrated horses effectively with enteral replacement solutions. Nasogastric fluids do not need to be sterile and can be made up on the farm and are therefore considerably cheaper and easier to transport than intravenous fluids. It is apparently not necessary to add glucose to enteral fluids for horses but, if at all possible, electrolytes should be added. Isotonic or hypotonic fluids should be administered. It is important to add a balanced electrolyte powder to the fluids. Plain water results in a decrease in the plasma tonicity, and the administered fluid is excreted via the kidneys to restore plasma osmolarity. Therefore, plain water does not restore circulating volume. Amounts to give The amount of fluid administered at any one time should not exceed six to eight litres for a 500 kg horse, with at least 30 minutes allowed to elapse between each administration. Before each dose, the stomach should be refluxed and the administration delayed if more than two litres of fluid are recovered. Repeated doses of nasogastric fluids overrun the capacity of the small intestine to absorb these fluids. This limits the quantity of ongoing fluid loss that can be replaced with nasogastric fluids (for example in colitis). Conversely, however, it provides a method for hydrating colonic material in large colon impactions. The author uses 5-6 litres of isotonic fluid by nasogastric tube for a 500kg horse with a primary pelvic flexure impaction, given at 30 minute intervals for 5 times. Some horses will show signs of abdominal pain when large doses of nasogastric fluids are administered, especially if the fluids are cold. Continuous nasogastric fluids with an indwelling tube have the advantage that they are much less likely to induce abdominal pain. The maximum rate administered should be 20ml/kg/hr. Often, the narrow bore of the feeding tube and giving set will limit the fluid rate to considerably lower than this, in the region of 5-6L an hour in a 500kg horse. Intravenous fluids in the field There are two situations in which intravenous fluids are given in the field. The first is to give the animal enough fluids to survive transportation to a hospital where further fluids will be provided. The second is to wholly treat the horse in the field. In this first situation, the horse or foal is extremely hypovolaemic and requires immediate fluid resuscitation. The plan should be centred on quickly placing a catheter and starting fluids. Often catheters will not survive transportation, particularly in foals, and therefore the priority is to quickly place a short-term catheter rather than taking a lot of time to place a long-term catheter. Wide-bore Teflon catheters (10-12ga in adults, 14-16ga in foals) placed in the jugular vein are ideal for this situation. The catheters need to be placed in a sterile fashion. At least 20ml/kg and up to 80ml/kg of isotonic crystalloid fluids (Lactated Ringer’s Solution, Hartmann’s solution, Normosol-R) need to be administered for treatment to be 3
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