Dexmedetomidine infusions improve cardiovascular and renal function in anaesthetised, experimentally endotoxaemic horses.

BACKGROUND Dexmedetomidine infusions are beneficial in anaesthetised endotoxaemic horses when administered concurrent to endotoxin, but post-conditioning effects are unknown.

OBJECTIVES To evaluate whether a dexmedetomidine infusion is beneficial in horses administered Escherichia coli O55:B5 lipopolysaccharides (LPS) endotoxin prior to anaesthesia.

STUDY DESIGN Randomised controlled in vivo experiment.

METHODS Ten systemically healthy horses were instrumented for acquisition of cardiac index (CI) using thermodilution. Horses received IV LPS (0.1 μg/kg bwt) immediately prior to anesthesia. Horses received IV xylazine (control, LPS; n = 5) or dexmedetomidine (treatment, LPS-Dex; n = 5), followed by IV ketamine and midazolam and sevoflurane in oxygen. In LPS-Dex, dexmedetomidine (1.75 μg/kg bwt/h IV) was administered and target end-tidal sevoflurane concentration was reduced (1.8% vs. 3% LPS). Cardiopulmonary function, acid-base, cytokine, and creatinine values were assessed every 30 min for 180 min. Data were compared between groups using mixed model analysis (p < 0.05).

RESULTS Mean ± standard deviation CI was significantly higher in LPS-Dex at 30 and 60 min (57.9 ± 15.6 mL/min/kg bwt versus 43.1 ± 9.4, 30 min, p = 0.03; 60.2 ± 11.8 mL/min/kg bwt versus 38.9 ± 11.2, 60 min, p = 0.003). Creatinine was elevated and significantly higher in LPS from 90 min onward but remained normal in LPS-Dex throughout (201 ± 38 μmol/L versus 124 ± 26, 180 min, p = 0.003). Significantly improved base excess values were seen in LPS-Dex at 150 and 180 min (2.9 ± 2 mmol/L versus 0.6 ± 1, 150 min, p = 0.03; 3.4 ± 1.96 mmol/L versus 0.6 ± 1.41, 180 min, p = 0.01). Cytokine concentrations were similar between groups.

MAIN LIMITATIONS The experimental protocol is not representative of all surgical colics.

CONCLUSIONS Dexmedetomidine infusion and concurrent reduction in inhalant anaesthetic could benefit anaesthetic management of horses even when endotoxaemia is already present.