Influence of midazolam premedication on intraoperative EEG signatures in elderly patients

•Frontal α-band power increases after induction of anesthesia with propofol.•Premedication with midazolam elevates the increase of frontal α-power after administration of propofol compared to non-premedicated patients.•α-power remains higher in premedicated patients during maintenance of anesthesia with propofol/volatile anesthetics. To investigate the influence of midazolam premedication on the EEG-spectrum before and during general anesthesia in elderly patients. Patients aged ≥65 years, undergoing elective surgery were included in this prospective observational study. A continuous pre- and intraoperative frontal EEG was recorded in patients who received premedication with midazolam (Mid, n = 15) and patients who did not (noMid, n = 30). Absolute power within the delta (0.5–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), and beta (12–25 Hz) frequency-bands was analyzed in EEG-sections before (pre-induction), and after induction of anesthesia with propofol (post-induction), as well as during general anesthesia with either propofol or volatile-anesthetics (intra-operative). Pre-induction, α-power of Mid patients was lower compared with noMid-patients (α-power: Mid: −10.75 dB vs. noMid: −9.20 dB; p = 0.036). After induction of anesthesia Mid-patients displayed a stronger increase of frontal α-power resulting in higher absolute α-power at post-induction state, (α-power: Mid −3.56 dB vs. noMid: −6.69 dB; p = 0.004), which remained higher intraoperatively (α-power: Mid: −2.12 dB vs. noMid: −6.10 dB; p = 0.024). Midazolam premedication alters the intraoperative EEG-spectrum in elderly patients. This finding provides further evidence for the role of GABAergic activation in the induction of elevated, frontal α-power during general anesthesia. NCT02265263. 23 September 2014. Principal investigator: Prof. Dr. med. Claudia Spies. (https://clinicaltrials.gov/ct2/show/NCT02265263).