Effects of noxious stimulation on the electroencephalogram during general anaesthesia: a narrative review and approach to analgesic titration

Electroencephalographic (EEG) activity is used to monitor the neurophysiology of brain, which a target organ general anaesthesia. Besides its use in evaluating hypnotic states, neurophysiologic reactions noxious stimulation can also be observed EEG. Recognising and understanding these responses could help optimise intraoperative analgesic management. This review describes three types changes EEG induced by when patient under anaesthesia: (1) beta arousal, (2) (paradoxical) delta (3) alpha dropout. Beta arousal an increase power beta-frequency band (12–25 Hz) response stimulation, especially at lower doses anaesthesia drugs absence opioids. It usually indicative cortical depolarisation increased activity. At higher concentrations anaesthetic drug, with insufficient opioids, (increased [0.5–4 Hz]) dropout (decreased [8–12 are associated stimuli. The mechanisms not well understood, but midbrain reticular formation seems play role. Alpha may indicate return thalamocortical communication, from idling mode operational mode. Each reflect incomplete modulation pain signals mitigated administration opioid or regional techniques. Future studies should evaluate whether titrating reduces postoperative influences other outcomes, including potential development chronic pain. Editor's key points•Processed electroencephalogram monitoring commonly state titrate agent administration.•Understanding identifying lead better antinociceptive/analgesic titration.•Nociception-induced include patterns.•This focuses on above patterns, discusses implications for analgesia management insights future research. •Processed expected that patients undergoing surgery neither experience nor remember procedure.1Rowley P. Boncyk C. Gaskell A. et al.What do people expect anaesthesia?.Br J Anaesth. 2017; 118: 486-488Abstract Full Text PDF PubMed Scopus (12) Google Scholar Furthermore, endure as little possible through adequate treatment throughout surgical intervention. A major challenge clinical care attenuation patients' stimulus. Traditionally, component predominantly titrated cardiovascular variables, most commercially available devices quantify autonomic (described next section). However, it important acknowledge nociceptive have many dimensions: somatic (spinal reflexes causing limb movement); (brain stem hypothalamic effects heart rate, ventilatory frequency, vasoconstriction, pupillary changes); cognitive memory (subcortical structures mediated via forebrain cortex attention memory); (4) various endocrine, coagulation, immune-inflammatory responses. significance (as measured frontal electrodes) less clear. These more transient occur concurrently reactions. they clear indications has, some way, failed fully suppress brain's surgery-induced tissue damage. degree this situation long-term outcomes unknown present. focus narrative article describe particular (frontal) recordings, underlying neurophysiological take least very different patterns. (e.g. maintenance volatile anaesthetics typically 0.5–1.0 MAC effect site concentration) react stronger oscillations range. called often occurs together movement reaction painful Other reactions, predominately administered medications during balanced (analgesics plus anaesthetics), Delta slow frequencies (0.5–4 Hz), decrease (8–12 Hz). Although appear biomarkers nociception, remains seen will consistently prevent their occurrence improve outcomes. Intraoperative consideration representative intense periods paradigm shift easily reviewed systematic, automated search strategies. We approached subject expanding previous knowledge using references found papers. Because we focused description patterns perioperatively tried group relevant literature into processed indices, raw EEG, findings animal models. Using EEG-derived information becoming common navigate With exceptions, EEG-based monitors done tracking low-amplitude, high-frequency wakefulness high amplitude, low frequency levels perform surgery.2Brown E.N. Lydic R. Schiff N.D. General anesthesia, sleep, coma.N Engl Med. 2010; 363: 2638-2650Crossref (643) widely indices Patient State Index (PSI™; Sedline, Masimo, Irvine, CA, USA),3Prichep L. Gugino John E. al.The indicator level hypnosis anaesthesia.Br 2004; 92: 393-399Abstract (64) bispectral index (BIS; Medtronic, Dublin, Ireland),4Rampil I.J. primer signal processing anesthesia.Anesthesiology. 1998; 89: 980-1002Crossref (1122) entropy (SE/RE; GE Healthcare, Helsinki, Finland).5Viertio-Oja H. Maja V. 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Many anaesthesiologists multi-dimensional mental