SUMMARY Response to 4 hours' infusion of 20 L of saline solution was studied in healthy horses given the usual feed and water and in horses dehydrated by feed and water deprivation. Seven healthy horses in 8 trials urinated an average of 8.9 L during the infusion period. The mean 24-hour urinary production was 20.8 L, containing 3,310 mEq, 2,122 mEq, and 3,901 mEq of sodium, potassium, and chloride, respectively. In contrast, only 1 of the 7 dehydrated horses urinated during the infusion. Mean 24-hour urine volume for the group was 9.1 L. Urinary sodium excretion (2,532 mEq) was not significantly different from that of the healthy horses, but potassium and chloride losses were significantly reduced (to 892 mEq and 2,918 mEq, respectively). Alterations in pcv , total plasma protein, and plasma sodium and chloride concentrations, and osmolality after the infusion were quantitatively similar in the 2 groups of horses. Significant reductions in pcv and total plasma protein persisted for 6 to 8 hours, and plasma potassium concentration was decreased for 4 to 6 hours. Plasma sodium concentration remained largely unchanged, and plasma chloride was significantly increased over preinfusion concentration for a period of 12 hours. The results of the study confirmed reports that the relative water deficit produced by feed and water deprivation is not readily corrected by infusion of saline solution. Since sodium and chloride depletions were not the primary problems, there was a nearly quantitative urinary excretion of the infused saline solution. The elimination of the excess sodium chloride required major renal adjustments and increased urinary water loss. A close relationship between net fluid retention (as indicated by change in body weight) and urine output was demonstrated.
The purpose of this study was to describe the pharmacokinetics of bromide in horses and to evaluate the corrected bromide space as an indicator of extracellular fluid volume (ECFV) in horses after the administration of a single dose of bromide by intravenous infusion. Sodium bromide (30 mg/kg of body weight, IV) was administered to 6 clinically healthy mares over a period of 3 minutes. Blood samples were collected before infusion and at intervals between 0.5 hours and 53 days after infusion. Mean elimination half‐life (harmonic mean) was 126 hours (5.2 days), clearance was 1.4 ± 0.09 mL/kg h, area under the curve was 17,520 ± 1,100 |jug h/mL, and volume of distribution (steady state) was 0.255 ± 0.015 L/kg. The mean corrected bromide space was determined from the volume of distribution (steady state) and the serum concentrations of bromide at equilibration. Corrected bromide space, an estimate of ECFV, was 0.218 ± 0.01 L/kg. The conclusion was made that ECFV of horses can be estimated by measuring bromide concentrations in a preinfusion serum sample and a sample obtained 5 hours after the administration of bromide. Key words: Fluid balance; Pharmacology.
