The ability of bispectral index to detect intra‐operative wakefulness during total intravenous anaesthesia compared with the isolated forearm technique

It has been suggested that monitoring during total intravenous anaesthesia should include aspects of brain function. The current study used a manually adjusted target‐controlled infusion of propofol for anaesthesia, guided to a bispectral index range of 55–60. Intra‐operative responsiveness, as assessed by the isolated forearm technique, was compared with whether the bispectral index predicted/identified a patient's appropriate hand movements in responses to commands. Twenty‐two women underwent major gynaecological surgery with total intravenous anaesthesia, propofol, remifentanil and atracurium. Sixteen women responded, on 80 occasions, with appropriate hand movements to commands during surgery, of which the bispectral index detected 47 (sensitivity 59%). The bispectral index suggested consciousness 220 times in the absence of movement responses (specificity 85%). The positive predictive value of a bispectral index response was 18%. While two women had vague recall about squeezing fingers, none had recall of surgery. For patients who responded more than once during surgery the bispectral index value associated with a response was not constant. Although there was no difference in the median (IQR range]) effect site propofol concentration between intra‐operative responses (2.0 (1.5–2.3 1.2–4.0]) μg.ml^?1) and eye opening after surgery (2.1 (1.7–2.8 1.5–3.9]) μg.ml^?1), the median (IQR range]) bispectral index value at eye opening after surgery was significantly higher than that associated with responses during surgery: 75 (70–78 51–93]) vs 61 (52–67 37–80]) respectively, (p < 0.001). The manual control of propofol intravenous anaesthesia to target a bispectral index range of 55–60 may result in an unacceptable number of patients who are conscious during surgery (albeit without recall).