Absence of typical intraopertative EEG signature of general anaesthesia and continuous suppresion ratio as detected with NeuroSENSE® depth-of-anaesthesia monitor allow considerable decrease of the dose of anaesthetic agents during cardiac surgery : A case report.

Background:A prominent feature of EEG under general anesthesia(GA)is anteriorisation of alpha(α) waves. Studies suggest that α power under GA reflects the degree of brain vulnerability. This would correlate with the increased percentage of EEG suppression in older adults with poor neurocognitive reserve. Case Report:A 63-year-old male(106kg) with history of diabetes,arterial hypertension,CVA(no sequella)and renal transplantation(GFR= 77mL/min/1.73m2)was schedulded for on pump CABG.After full monitoring including frontal EEG (NeuroSENSE®) and NIRS,GA was induced with 2mg midazolam,50 mg propofol,50μg sufentanil and 25mg ketamine.Because of the appearance of bilateral suppression ratio (SR)despite perfect hemodynamics no anesthetic was administered during the insertion of CV line.He continued showing SR (Fig1).Flumazenil(0.4mg) was administered with no effect.A 8 channels-EEG(Datex-Ohmeda)confirmed the observations(Fig 2).International 10-20 EEG was performed showing very slowed(δ and sub-δ)hypovoltaged EEG without asymmetry.A decision to do off pump CABG was taken.Surgery was performed under 0.4% exp sevoflurane and remifentanil at 0.02μg/kg/min. NeuroSENSE® spectral analysis showed only delta waves in absence of α frequencies till the end. He was extubated 2h after arrival in the ICU and showed neither awareness nor neurological complications till hospital discharge. Discussion:This is an example of extreme sensitivity of the aged/frail brain to anesthetics and illustrates that age-related EEG changes can be extremely enhanced in some cases. Learning points:Our case confirms that typical EEG signatures of GA may be absent in patients with poor brain reserve and EEG SR reflects this vulnerability.It moreover illustrates the importance of intraoperative EEG monitoring to avoid anesthetic overdoses.