Blood glucose, acid-base and electrolyte changes during loading doses of alpha₂-adrenergic agonists followed by constant rate infusions in horses.

This study investigated how the use of two alpha2-adrenergic agonists, xylazine and romifidine, in horses affected blood glucose levels, acid-base status, and electrolyte concentrations.

Design of the Study

• The investigation employed a blinded, randomized, crossover design with seven horses treated either with xylazine or romifidine, both types of alpha2-adrenergic agonists (medications often used for sedation).
• The horses were first given an intravenous bolus (an amount of substance given all at once rather than gradually) of either xylazine (1mg/kg) or romifidine (80 μg/kg).
• This was followed by an intravenous constant rate infusion (a stable, ongoing administration of a drug over a certain period of time) of xylazine (0.69 mg/kg/h) or romifidine (30 μg/kg/h) over a span of 2 hours.

Method of Data Collection

• Blood samples were drawn before and after the loading doses, during the constant rate infusion, and one hour after the drugs had been discontinued.
• This allowed for a comprehensive timeline of changes in each horse’s blood glucose concentration, base excess (which helps measure the acid-base balance within the body), pH levels, partial pressure of carbon dioxide, strong ion difference (which aids in diagnosing acid-base disorders), bicarbonate concentration, sodium concentration, chloride concentration, and anion-gap (a value calculated from the electrolytes tested in a basic metabolic panel).

Study Results

• Both drugs were observed to significantly increase blood glucose, base excess, pH levels, partial pressure of carbon dioxide, strong ion difference, and bicarbonate concentration, indicating alterations in the acid-base balance and electrolyte levels of the horses.
• Chloride concentration and anion-gap decreased notably compared to baseline measurements. The decrease in sodium concentration was considerable only with xylazine.
• Interestingly, one hour after the start of the constant rate infusion, blood glucose concentration was significantly higher in horses treated with romifidine as opposed to xylazine. Again, one hour after discontinuing the drugs, all variables except for blood glucose concentration, strong ion difference, and partial pressure of carbon dioxide returned to normal values in the case of xylazine. Romifidine, however, caused persistent alterations in all variables except pH for at least 1 hour.

Study Conclusion

• The researchers concluded that loading doses of alpha2-adrenergic agonists, followed by constant rate infusions, do indeed influence blood glucose concentration, acid-base status, and electrolyte concentrations in horses.
• The real-world clinical implications of these observed changes remain uncertain and should be interpreted with caution, especially given the use of fluid boli for cardiac output measurements.
• The importance of these changes may come into play during extended drug infusions and in treatment of critically ill patients where strict control of these factors is vital.