Monitoring the brain: processed electroencephalogram and peri‐operative outcomes

Abstract

Summary Although the brain is the target organ of general anaesthesia, the utility of intra‐operative brain monitoring remains controversial. Ideally, the incorporation of brain monitoring into routine practice would promote the maintenance of an optimal depth of anaesthesia, with an ultimate goal of avoiding the negative outcomes that have been associated with inadequate or excessive anaesthesia. A variety of processed electroencephalogram devices exist, of which the bispectral index is the most widely used, particularly in the research setting. Whether such devices prove to be useful will depend not only on their ability to influence anaesthetic management but also on whether the changes they promote can actually affect clinically important outcomes. This review highlights the evidence for the role of bispectral index monitoring, in particular, in guiding anaesthetic management and influencing clinical outcomes, specifically intra‐operative awareness, measures of early recovery, mortality and neurocognitive outcomes.

The 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia: summary of main findings and risk factors

“…Also, in studies using the Brice interview, a low proportion (about one third) of patients report pain or distress associated with their AAGA experience (i.e. the majority appear to make a neutral report) [7,8,31]. This is similar to the proportion reporting distress in the NAP5 baseline survey [2], but somewhat lower than the 50% we have reported [29].…”

Clarifying NAP5

“…Thus to correct the data they quote, the NAP5 estimates of 'incidence of reports' actually lie between 1:670 (for obstetrics; remarkably close to a Brice incidence) to 1:136 000 (when no neuromuscular blockade is used). These wide estimates do not reflect some imprecision on our part, but are very robust data and indicate to us that AAGA is not a single entity [5,6]. The 'doughnut' diagram in Absalom and Green's editorial [7] (itself based upon a bar chart presented elsewhere [8]) nicely encapsulates this notion.…”

Definitions of anaesthetic technique and the implications for clinical research

“…A positive correlation with clinical sedation scores has consistently been demonstrated [7], but precision is limited by wide inter-individual and interagent variability. There are no specific values on any of the scales which reliably predict level of sedation, or the transition for consciousness to unconsciousness, in a given individual [8,9]. Furthermore, each pharmacological agent has its own distinct spectrum of values for a given level of sedation [8,10] and specific problems arise with the use of ketamine and opioid analgesics, both of which disrupt the correlation between sedation and bispectral index [11].…”