The bispectral index (BIS) summarizes aspects of the brain’s electrical activity. Pulse oximetry estimates blood oxygen saturation. A prospective plastic-surgery study illustrates how the two measurements can diverge during the same procedure.
In 97 patients who received midazolam and ketamine under a preset protocol, researchers recorded BIS at four points in the first 20 minutes after midazolam. They separately tracked oxygen saturation below 90%. Twelve patients crossed that oxygen threshold. Their mean BIS was 81.1, compared with 83.3 among the other patients, and the difference was not statistically significant.
The comparison used group averages and relatively few oxygen events. It provides no validated BIS cutoff for detecting a desaturation. In a retrospective review, the timestamped oxygen trace and documented airway interventions address when oxygen levels dropped and what happened next. BIS values add information about the monitored brain signal during sedation.