Effect of alfaxalone infusion on the electroencephalogram of dogs anaesthetized with halothane

Objective To describe the effects of alfaxalone on the canine electroencephalogram (EEG). Study design Experimental study. Animals Eight healthy adult Huntaway dogs. Methods Anaesthesia was induced with propofol and maintained with halothane (0.85-0.95 end-tidal volume %) in oxygen. Animals were ventilated to maintain stable end-tidal CO₂ and halothane concentrations. Following a 30minute stabilisation period, alfaxalone (0.5mgkg^-1) was infused intravenously over a 5minute period. The electroencephalogram was recorded from the beginning of the stabilisation period until 60minutes following the start of alfaxalone treatment. Data were subjected to fast Fourier transformation, and median frequency, 95% spectral edge frequency and total EEG power were calculated. Two-factorial repeated measures anova (time and EEG channels were factors) was used for statistical analysis (p<0.05). Results A shift in the dominant frequency band from beta to delta after alfaxalone treatment and occasional burst suppression were observed. Median frequency decreased significantly below baseline (9.2±1.4Hz) (mean±SD) during alfaxalone infusion. The lowest value (4.8±1.2Hz) was recorded 5minutes after the start of infusion. Spectral edge frequency also decreased below baseline (26.2±1.5Hz) and the lowest value (22.6± 1.5Hz) also was detected at 5minutes after the start of infusion. Total EEG power did not change significantly. In some frequencies EEG power increased soon after the start of alfaxalone infusion, then decreased below baseline later (biphasic pattern). Conclusions and clinical relevance Alfaxalone induced biphasic changes on EEG and decreased F₅₀ and F₉₅ in halothane anaesthetized dogs.