Why we started
Roughly 60,000 people in the United States receive general anesthesia every day.¹ More than a third of inpatient surgical procedures are performed on patients 65 or older.² The standard governing how all of them are monitored requires four things to be evaluated continually: oxygenation, ventilation, circulation, and temperature.³ It was first adopted in 1986. It was last amended in October 2025. In neither version, nor in any between, does it ask for a measure of the brain, which is the organ anesthetic drugs act on.
The brain can be measured. Under general anesthesia, it produces a distinct electrical signature, including a slow alpha rhythm at the front of the head that arrives with loss of consciousness. An EEG reads it through the skin of the forehead.
The difficulty is what the industry built on top of that signal. Depth-of-anesthesia monitors compress the EEG into a single number, and the ones in clinical use were developed largely on younger adults. In a study of 155 patients aged 18 to 90, EEG oscillations in elderly patients were roughly two to three times smaller in amplitude than in younger adults, with alpha power falling furthest of all.⁴ The authors' own conclusion was that commercial depth-of-anesthesia indices do not account for age and are therefore likely to be inaccurate in elderly patients.⁴ The error runs in one direction. A brain state that reads as adequately anesthetized at 40 can read as too light at 80, and the patient is given more drug. Older patients are correspondingly more likely to enter burst suppression, the deepest anesthetic state, in which the EEG falls silent for seconds at a time.⁴,⁵
That matters because anesthetic exposure is one of the few modifiable contributors to postoperative delirium, which affects between 13 and 42 percent of older surgical patients⁶ and costs Medicare an average of $44,291 per patient in the year that follows.⁷ The cost is not the patient's alone. When researchers scored delirium-related distress on a five-point scale, patients who recalled the episode averaged 3.2 and the nurses caring for them averaged 3.09. The highest score belonged to a third group: the spouses and caregivers sitting beside the bed, at 3.75.⁸
In 2018, three doctor and engineers from MIT set out to fix the measurement.
