Effects of lidocaine bolus and infusion on neuromonitoring by bispectral index (BIS®), electroencephalogram periodic and aperiodic activity, and Surgical Pleth Index® during propofol-remifentanil anaesthesia: a single-centre prospective observational study.

BACKGROUND: Lidocaine administration during stable propofol-remifentanil anaesthesia causes a decrease in bispectral index (BIS®), although its influence on hypnosis is debated. We evaluated dose-dependent lidocaine effects on spectral EEG features and the processed parameters BIS and 95% spectral edge frequency (SEF95). METHODS: We conducted an observational, prospective, single-centre study analysing intraoperative data from 20 adult female patients undergoing breast surgery. During stable propofol-remifentanil target-controlled infusion, we delivered an i.v. lidocaine bolus (1.5 mg kg-1) over 10 min, followed by a 30 min infusion at a rate of 1.5 mg kg-1 h-1. We evaluated the lidocaine-induced change in EEG spectral composition, including aperiodic and periodic features, BIS, SEF95, and Surgical Pleth Index® (SPI). RESULTS: We observed an increase in delta-band EEG activity and a decrease in beta-band EEG activity 4 to 6 min after the bolus, whereas BIS and SEF95 did not change significantly. The alpha peak features bandwidth and centre frequency also decreased significantly in the early period. The aperiodic slope slightly but significantly increased after the bolus and during infusion. During the infusion phase, BIS and SEF95 significantly decreased after 12 to 15 min, as did SPI in the later stages of the infusion phase. CONCLUSIONS: When lidocaine is given during stable propofol-remifentanil anaesthesia, changes in spectral EEG parameters occur earlier than changes in BIS, SEF95 and SPI. The observed EEG and SPI changes are consistent with a predominant antinociceptive contribution to the anaesthetic-sparing effects of lidocaine, although the physiological interpretation of the derived parameters remains an evolving area of research. CLINICAL TRIAL REGISTRATION: NCT06135688.