Unconventional monitoring methods. can BIS® predict airway obstruction?

Anaesthesia depth assessment is still under discussion despite several monitors available to this day (BIS®, Entropia®, SED-line®, NarcoTrend® etc). Since manufacturer introduced the BIS device in 1994, a huge debate raised about its real usefulness in monitoring anaesthesia depth and preventing awareness. Just to mention the main studies that have been published about BIS, in 2004 the "B-Aware Trial" showed better outcomes for adult patients at high risk of awareness1; in 2008 the "B-Unaware Trial" demonstrated no differences in awareness incidence when BIS is compared to end-tidal anaesthetic gas (ETAG) measurement2. In 2007, Manyam discussed the need to maintain BIS reading below 60, demonstrating how BIS values are minimally influenced by the addition of opioids to general anaesthetics3. In 2011, the BAG-RECALL Research Group was unable to prove superiority of BIS-guided anaesthesia versus ETAG-guided anaesthesia4. More recently, Mashour et al. found no differences in the incidence of awareness in a study with more than 21.000 patients5. A 2014 Cochrane review confirmed the previous trend, finding inconclusive evidence of intraoperative awareness protection6. In addition, in 2015, the BJA released a special issue about memory and awareness, from which two studies are worth mentioning: a study by Schuller, in which BIS monitor was used in awake volunteers receiving neuromuscular blocking agents, showing unreliable values7, and a review on "controversies and non-controversies" in intraoperative awareness8