THE EFFECTS OF EQUIVALENT DOSES OF TROMETHAMINE OR SODIUM-BICARBONATEIN HEALTHY HORSES

Objective-To describe the effects of tromethamine, a putative treatmen t for metabolic acidosis, and to compare its biochemical effects with those of sodium bicarbonate. Design-Randomized intervention study with repeated measures. Animals-16 healthy horses, 3 to 17 years old, weig hing 391 to 684 kg. Methods-Ten horses received 3 mEq/kg tromethamine and six received 3 mEq/kg sodium bicarbonate. Samples of venous blood and cerebrospinal fluid (CSF) were collected at intervals before and a fter drug administration. Heart rate and breathing rate were also reco rded at intervals. Results-Median standard base excess increased signi ficantly (P <.05) from baseline immediately after both bicarbonate and tromethamine. These increases were not significantly different betwee n treatments. Standard base excess returned toward baseline but remain ed significantly increased 3 hours after infusion of either treatment. After tromethamine, there was a significant decrease in plasma sodium concentration that lasted for at least 90 minutes. After sodium bicar bonate, no change in plasma sodium concentration was detected. Both so dium bicarbonate and tromethamine increased carbon dioxide tension in venous blood and CSF. Despite venous alkalemia, the pH of CSF decrease d after both treatments. Conclusions-Tromethamine and sodium bicarbona te have similar alkalinizing ability. Tromethamine causes hyponatremia , whereas both tromethamine and sodium bicarbonate increase carbon dio xide tension in venous blood and CSF. Clinical Relevance-If hyponatrem ia, hypercarbia, and acidosis of the CSF occur after tromethamine is g iven to horses with existing metabolic acidosis, some of the potential advantages of tromethamine may prove theoretical rather than practica l. (C) Copyright 1998 by The American College of Veterinary Surgeons.