False Negative BIS? Maybe, Maybe Not!: In Response

BIS Monitoring: Awareness and Catastrophic Events

The bispectral index is an electroencephalogram-based monitoring tool to help anesthesiologists determine depth of anesthesia. The bispectral index indicates both the potential for awareness and of relative hypnotic overdose, but it does not predict movement or hemodynamic responses to stimulation, and it cannot predict the exact moment consciousness returns. The bispectral index has been assessed for its relationship to awareness, and bispectral index monitoring appears to be generally associated with a low incidence of awareness. The bispectral index has also has been noted to detect periods of cerebral ischemia. It is also being used in intensive care units to help quantify the level of sedation in patients and as an outcome predictor in patients with brain injuries. Low values of the bispectral index often occur during catastrophic, ischemic, events but the use of this technology for the routine monitoring of such events is unproven.

[Awareness: a problem in paediatric anaesthesia?]

Intraoperative awareness has been reported to occur in 0.8-5.0% of paediatric patients undergoing anaesthesia and, therefore, seems to be more common than in adults (incidence 0.1-0.2%). In adult patients, the consequences of intraoperative awareness are well known and can be severe, in children, however, they have not yet been adequately studied. The causes for intraoperative awareness can be divided into three broad categories: First, no or only a light anaesthetic is given on purpose, second, an insufficient dose of an anaesthetic is given inadvertently, third, there is equipment malfunction or the anaesthesiologist makes an error. Unfortunately, especially in young children, painful interventions are still performed without adequate analgesia, e.g. awake intubation or fracture manipulation under midazolam sedation alone. The key issue is, however, that pharmacokinetics and pharmacodynamics change enormously from the 500 g preterm baby to the adolescent patient. Adequate dosing is much more difficult in paediatric patients compared to standard adult surgical patients. Solid knowledge of the pharmacokinetic and pharmacodynamic characteristics of commonly used drugs in different paediatric age groups, as well as aiming for perfection in daily care will help to reduce the incidence of awareness. Methods for monitoring the depth of hypnosis, e.g. the bispectral index, will be used increasingly, at least in children above 1 year of age. In addition to clinical parameters, they will hopefully help to further reduce the incidence of intraoperative awareness.

Processed EEG and patient outcome

The era of research evaluating clinical outcomes associated with processed electroencephalogram (EEG) monitoring began with the first randomized trial of bispectral index monitoring (BIS) performed as part of the clearance process for approving routine clinical use of the BIS monitor by the United States Food and Drug Administration. Subsequent to this initial investigation, numerous other clinical investigations have demonstrated that the use of processed EEG monitors as an additional method of patient assessment and an aid to anaesthetic dosing can decrease anaesthetic usage and hasten recovery times. Because of the presumed association between anaesthetic effect and EEG changes, it is not surprising that the additional research has focused on the impact of processed EEG monitoring on postoperative outcomes and perioperative safety especially the prevention of intraoperative awareness.