Electroencephalographic and Cardiovascular Assessments of Isoflurane-Anesthetized Dogs.

This study investigated the use of frontal electroencephalography (EEG) to monitor varying levels of isoflurane anesthesia in dogs. The patient state index (PSI), burst suppression ratio (SR), and waveforms, were continuously recorded while mean arterial blood pressure (MBP), heart rate, responses to electric stimuli, and subjective anesthetic "depth" were assessed every 3 min. At deep anesthesia (2.5× MAC - 3.2%), the PSI (6.5 ± 10.8) and MBP (45.6 ± 16.4 mmHg) were the lowest, and SR was the highest (78.3 ± 24.0%). At 1× MAC (1.3%), the PSI and MBP increased significantly to 47.8 ± 12.6 and 99.8 ± 13.2, respectively, and SR decreased to 0.5 ± 2.5%. The EEG was predominantly isoelectric at 2×-2.5× MAC, indicating unconsciousness and unresponsiveness. As anesthesia lightened, waveforms transitioned to flatter and faster activity patterns with a response to noxious stimuli, suggesting regained consciousness. The PSI and MBP exhibited a stronger correlation (ρ = 0.8098,