Peri-operative neurological monitoring with electroencephalography and cerebral oximetry: a narrative review

Surgery and anaesthesia subject the brain to considerable stress in the peri-operative period. This may be caused by potentially neurotoxic anaesthetic drugs, impaired cerebral perfusion and reperfusion injury related to surgery or thromboembolic events. Patient monitoring using electroencephalogram and cerebral oximetry can assist in optimising depth of anaesthesia and assessment of cerebral metabolic activity. However, research findings have been contradictory as to whether these monitors can help ameliorate peri-operative neurocognitive complications. In this narrative review, we will discuss recent evidence in the use of electroencephalography and cerebral oximetry and the underlying scientific principles. It is important to appreciate the raw electroencephalographic changes under anaesthesia and those associated with ageing, in order to interpret depth of anaesthesia indices correctly. Cerebral oximetry is useful not only for the detection of cerebral desaturation but also to identify those patients who are particularly vulnerable to injury, for better risk stratification. An algorithm-based approach may be most effective in managing the episodes of cerebral desaturation.