Midazolam and flumazenil in neuroanaesthesia

Of the numerous benzodiazepines currently available, only a few are used in anaesthetic practice. Midazolam is utilised as a premedicant, sedative, and an induction agent and produces minimal depression of ventilation or of the cardiovascular system. The anticonvulsant activity is similar to that of diazepam. In neuroanaesthesia midazolam may be an acceptable alternative to other intravenous induction agents like barbiturates or etomidate in patients with compromised intracranial compliance. Midazolam produces dose-related reductions in cerebral blood flow and cerebral oxygen consumption. However, midazolam does not necessarily prevent increases in intracranial pressure during induction of anaesthesia. In the electroencephalogram (EEG) midazolam produces a reduction in alpha-activity, an increase in theta-delta-activity and low-voltage beta-activity. Midazolam like other benzodiazepines does not affect early components of auditory and somatosensory evoked responses, whereas late cortical responses may be suppressed. Flumazenil, a specific benzodiazepine antagonist, has been demonstrated to be effective in reversing benzodiazepine-induced sedation. In the EEG midazolam-induced changes vanish almost instantaneously. Flumazenil is also effective in restoring the amplitudes of cortical auditory and somatosensory evoked responses. However, as has been demonstrated in head-injured patients and animal experiments after incomplete cerebral ischaemia, increases in cerebral blood flow and intracranial pressure cannot be excluded after flumazenil administration. When utilising flumazenil for wake-up procedures in midazolam-sedated patients with pathological intracranial compliance, flumazenil has to be titrated very carefully in low doses over prolonged periods.