Battling Dehydration in Horses with Hypertonic Saline (AAEP 2010)

When horses have hemorrhaged or have experienced fluid losses from dehydration, they can end up in a dangerous state of low blood volume, called hypovolemia. Veterinarians use hypertonic saline to restore blood pressure while administering additional fluids, plasma, or blood to restore fluid volume. Langdon Fielding, DVM, Dipl. ACVECC, of Loomis Basin Equine Medical Center, in Loomis, Calif., reviewed the use of hypertonic saline for multiple equine conditions at the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md.

Fielding explained that in a Robin Hood-like effect, tissues rich in fluid are forced to redistribute to areas poor in fluid. This creates dual effects--fluid loss in tissue means excess edema (fluid swelling) is eliminated while spaces gaining physiologic "water" restore rapidly along with improved blood pressure. A horse in need of fluid restoration shows specific clinical signs: rapid heart rate, weak pulse, pale mucous membranes, delayed capillary refill time, slow jugular vein refill, cold extremities, and reduced urine output.

For blood loss, moderate dehydration, or shock, Fielding recommends administering two liters of hypertonic saline (per average 500-kg, or 1,100-lb. horse) followed immediately by administering intravenous (IV) isotonic fluids and perhaps additional oral fluids. Fielding pointed out a few things veterinarians should consider before reaching for hypertonic saline: If the hemorrhage has not been well-controlled, then raising blood pressure with hypertonic saline might exacerbate bleeding and, therefore, might not be the best choice of therapy. Also, for marked dehydration, he cautioned veterinarians about using hypertonic saline as there might not be sufficient tissue fluid to "steal" to restore the extracellular space--in these cases, such as with dehydrated endurance horses, concurrent restoration with isotonic IV fluids and oral supplementation of water are extremely important strategies.

Fielding also suggested using hypertonic saline (1/2 liter given three to four times a day per 500-kg horse) to combat edema formation subsequent to traumatic injury to the central nervous system, particularly as a substitute for mannitol (often used to reduce brain swelling). Horses with gastrointestinal disease that caused large fluid losses through diarrhea benefit from restoration with hypertonic saline. New research suggests that hypertonic saline might mitigate effects of intestinal shutdown (ileus) in colic by reducing bowel edema severity. And, by boosting blood pressure, hypertonic saline provides a rapid rescue treatment for refractory hypotension (low blood pressure of unapparent cause) that can occur during anesthesia.

Severe electrolyte derangements complicate use of hypertonic saline administration, and veterinarians must take care when treating horses with kidney or other organ dysfunction using this method.

Fielding said he is impressed by the growing number of practical uses for hypertonic saline, the ability to administer this therapy rapidly in minutes rather than hours, and also by how easily a veterinarian can store this relatively inexpensive product on an ambulatory veterinary truck without it taking up much space.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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