text: Differential effects of propofol and isoflurane on the relationship between EEG Narcotrend index and clinical stages of anaesthetic depth in sheep undergoing experimental cardiac surgery.
  The electroencephalogram (EEG) Narcotrend index (NI) has been shown to improve anaesthetic depth monitoring in isoflurane-anaesthetised sheep. Data obtained from 13 anaesthetised juvenile female sheep were analysed retrospectively in order to assess the relationship between clinical stages of anaesthesia (CS) and NI during both propofol and isoflurane anaesthesia. Polynomial regression analysis revealed no significant association between CS and NI for propofol (R = 0.374, R(2) = 0.140, P = 0.403) but for isoflurane anaesthesia (R = 0.548, R(2) = 0.301, P = 0.010) there was a significant relationship. Furthermore, a strong correlation existed between end-tidal isoflurane concentration (ISOET) and CS (r = -0.463, P = 0.008). A combination of assessment of clinical signs and analogous EEG patterns is recommended during propofol anaesthesia.