Bispectral index

[2] The BIS was introduced by Aspect Medical Systems, Inc. in 1994[3] as a novel measure of the level of consciousness by algorithmic analysis of a patient's electroencephalogram during general anesthesia.

This is used in conjunction with other physiologic monitoring such as electromyography to estimate the depth of anesthesia in order to minimize the possibility of intraoperative awareness.

The US Food and Drug Administration (FDA) cleared BIS monitoring in 1996 for assessing the hypnotic effects of general anesthetics and sedatives.

[6] Additionally, BIS values less than 40 for greater than 5 minutes have been associated with increased risk of stroke (hazard ratio of 3.23), MI (1.94) and death (1.41).

As with other types of EEG analysis, the calculation algorithm that the BIS monitor uses is proprietary, although it has been successfully reverse engineered.

Some of the benefits that have been attributed to it include:[9] The BIS is an electroencephalogram-derived multivariant scale that, when a drug such a propofol is used, correlates with the metabolic rate of glucose.

[14][18] A Cochrane review in 2014[19] found that "Four studies (7761 patients) that used clinical signs as a guide to anaesthetic administration in standard practice, as the control group, demonstrated a significant reduction in the risk of awareness with BIS monitoring.

In fact, they cite an American Society of Anesthesiologists (ASA) statement saying that the decision for cerebral function monitoring should be made on an individual basis.

In some cases, the BIS may underestimate the depth of anesthesia, leading the anesthetist to administer a higher than necessary dose of anesthetic agent(s).

[31][32] Specifically for intraoperative awareness, according to a 2013 article in The Atlantic, "Today, the BIS monitor has become the most controversial medical device in anesthesiology, if not all of surgery.