A faculty dry run, a student presentation, and a bigger lesson about how anesthesia clinicians should think about postoperative delirium, cognitive decline, and processed EEG.
There is a phrase that gets used far too often in anesthesia education:
“The evidence is mixed.”
Technically, that is often true. But in practice, it can become a lazy escape hatch — a way to avoid the harder job of explaining what is actually mixed, why it is mixed, and what a clinician should do with the information when caring for a real patient.
But the most interesting thing about the session was not the slide deck.
It was the struggle to translate a dense, nuanced evidence base into a message an anesthesia audience could actually follow.
Why this conversation matters
The student’s framing was exactly the right place to start: older adults are particularly vulnerable to postoperative neurocognitive complications after general anesthesia. In the dry run, he separated postoperative delirium from postoperative cognitive decline in a way many talks fail to do. Delirium was described as a fluctuating disturbance in attention and awareness occurring in the first 24 to 72 hours after surgery, while postoperative cognitive decline was presented as a more persistent deficit that may last weeks, months, or even longer. That distinction is not academic trivia. It is the entire conversation.
Because when those two outcomes get blurred together, people start making crude summary statements like: “BIS works” or “BIS doesn’t work.” But postoperative delirium and postoperative cognitive decline are not interchangeable endpoints, and the literature should not be interpreted as though they are.
The case that makes the issue hard to ignore
One of the strongest moments in the dry run was a case vignette involving a 77-year-old man undergoing hemicolectomy under general anesthesia. During the case, he developed sustained electrocerebral silence despite otherwise non-catastrophic hemodynamics. The point was simple and powerful: without EEG monitoring, that brain state would have been invisible. At one-month follow-up, the patient had postoperative cognitive decline.
No, one case does not prove causation. But it does force the right question:
Why are we so comfortable acting directly on the brain while accepting so little direct information about brain state in many cases?
We monitor blood pressure continuously. We monitor oxygenation continuously. We monitor ventilation continuously. We monitor temperature and neuromuscular function. Yet when it comes to the organ most immediately altered by anesthetic drugs, some clinicians still act as though deeper brain monitoring is optional, academic, or somehow peripheral.
That tension sits right underneath the BIS debate.
BIS is not a cure. It is a window.
A lot of confusion in this space comes from asking the wrong question.
The question is not, “Does placing a BIS sensor reduce delirium?” Of course not.
The better question is, “Does the use of BIS meaningfully change clinician behavior in a way that reduces unnecessary anesthetic exposure or harmful EEG states in vulnerable patients?” That is a very different standard.
A BIS monitor is not a magic sticker. It is a piece of information. Like an arterial line, it matters only if the clinician understands what they are seeing and responds appropriately. The student’s presentation was at its best when it moved toward that interpretation-based view rather than treating BIS as a simple scoreboard. His talk also emphasized that the monitoring has to be interpreted in context, with attention to EEG patterns and age-related changes in the elderly brain.
That is the mature way to talk about processed EEG.
Where the evidence starts to get messy
The dry run then moved into the literature review, and this is exactly where many otherwise good presentations lose the room.
The student discussed early studies such as Ballard and Chan, describing favorable findings for postoperative cognitive decline and delirium, and then contrasted those with later systematic reviews. He highlighted a 2018 Cochrane review supporting benefit with titrated anesthesia, then a 2022 meta-analysis by Chu et al. reporting a reduction in postoperative cognitive decline but not postoperative delirium.
That is the point where many speakers start reciting references instead of teaching. But the real educational challenge is not remembering the chronology. It is helping the audience understand why the conclusions diverge.
And that is where the ENGAGES trial becomes central.
Why ENGAGES changed the conversation — and why that still may not settle it
In the dry run, the student correctly identified ENGAGES as a major reason many clinicians now feel justified saying BIS or processed EEG guidance makes no meaningful difference for postoperative delirium. He described ENGAGES as a 2019 trial of 1,232 elderly patients randomized to processed EEG-guided anesthesia versus usual care, with the goal of avoiding EEG suppression by keeping BIS greater than 40. He noted that delirium incidence was 26% in the EEG-guided group and 23% in the usual care group, while the reduction in anesthetic administration was modest and the between-group difference in burst suppression exposure was small.
That is a very important point. Because a negative trial is not always the same thing as a failed concept.
Sometimes it means the intervention did not produce enough physiologic separation between groups to answer the clinical question cleanly. The student argued exactly that, contrasting ENGAGES with earlier trials like CODA, where the differences in time spent at lower BIS values appeared much larger. He pointed out that in ENGAGES the practical separation in anesthetic exposure was small, including only about a 0.11 MAC difference between groups. That is the nuance too many people skip. To say “ENGAGES was negative, therefore BIS does not matter” is a much stronger claim than the trial itself can justify.
A more honest interpretation is this: if EEG-guided care does not substantially change depth-related exposure, suppression burden, or clinician behavior, then it may not improve delirium outcomes. That is not the same as proving that better brain-guided anesthetic titration has no value.
The hidden lesson from the dry run
The biggest lesson from the faculty session had less to do with BIS itself and more to do with how clinicians teach controversial evidence.
At one point, I specifically challenged the student to think about how to explain the difference between ENGAGES and CODA to an anesthesia audience that does not care much about EEG. My point was straightforward: if you cannot explain it in under a minute in a way people can follow, then you probably do not own the concept tightly enough yet. That is true far beyond this one topic.
In anesthesia education, learners often think mastery means adding more detail. Often the opposite is true. Mastery is being able to strip the explanation down to its load-bearing beams:
Postoperative delirium and postoperative cognitive decline are different outcomes. BIS is not a cure. Processed EEG only helps if it meaningfully changes care.
Negative trials must be interpreted in the context of how different the intervention group really was from usual care. And elderly patients deserve a brain-focused anesthetic strategy, not just a hemodynamic one. That is the talk. Everything else is supporting structure.
My own take
I do not think BIS should be oversold.
I do not think a single processed value should replace clinical judgment.
I do not think every favorable study proves causation, and I do not think every negative study should be dismissed.
But I also do not find the phrase “BIS makes no difference” to be a serious summary of this topic, especially in older adults.
A better conclusion is this:
Processed EEG is imperfect, but it gives us access to information about the organ most affected by our drugs. In elderly patients — where vulnerability to postoperative delirium and cognitive decline is real — that information may matter a great deal, especially when it helps clinicians avoid unnecessarily deep anesthesia, prolonged suppression, or blind trust in end-tidal agent concentration alone. The real question is not whether BIS is magic. The real question is whether we are willing to anesthetize the aging brain without listening to it.
That is why this topic is worth teaching. And just as importantly, that is why it is worth teaching well.