Hacker News Reader

Comment by bts327 | Hacker News Reader

I’m good here. Thanks.

MAC doesn't indicate the depth of the anesthesia. It indicates the depth of the paralysis. Which is exactly the problem EEG monitoring is supposed to prevent: In some cases patients can have an insufficient response to analgesia (so they will feel pain) and hypnotics (so they are awake, aware and forming memories) but will respond to paralytics (so they are unable to move and communicate their predicament).

So with this kind of practice, you create any patient's worst nightmare: being cut open, feeling everything, knowing everything, but unable to stop it. And you are unknowing, uncaring or too cheap to prevent that e.g. via EEG monitoring.

Edit: Parent removed his comment. Roughly, from memory, there was some claim by him about being a professional anesthetist, having very rarely encountered EEG and only bi-spectral index monitoring (an EEG-derived computed measurement) in some IV cases, some claims about the unreliability of both and about the preference for MAC (minimum alveolar concentration) to monitor depth of anesthesia.

Good day to you.

Well... My textbook[0] says:

> The minimum alveolar concentration (MAC) is the minimum concentration of an inhaled anesthetic at 1 atm of pressure that prevents skeletal muscle movement in response to a surgical incision in 50% of patients.

So first, you do not measure the depth of anesthesia, you measure the concentration of the anesthetic. Second, you judge this concentration by the prevention of muscle movement. Called paralysis.

Please tell me you are not really a doctor.

[0] https://www.sciencedirect.com/topics/medicine-and-dentistry/...

Edit: In case you are wondering why this response doesn't really fit the parent comment, the parent saw fit to completely replace his comment without an indication that he did so. Originally there was a claim in the parent comment about "MAC being the primary indication of anesthetic depth being the textbook definition" or something to that effect. To which I responded. I guess I must have hit a nerve there ;)

"MAC being the primary indication of anesthetic depth being the textbook definition"

I am an attending anesthesiologist and this is true. MAC cannot be interpreted at face value, though. You've got other drugs on board (not accounted for in MAC), the patient might be frail or very old, etc. etc. All things changing MAC interpretation, which is why there are still anesthesia providers instead of robots ;-) We currently have no way of faithfully measuring the depth of anesthesia, and our understanding of consciousness/awareness is incomplete. Anesthesiologists have to rely mostly on know-how, even in 2025.

>Robotic Anesthesia: A Vision for 2050

https://journals.lww.com/anesthesia-analgesia/fulltext/2024/...

>Anesthesia Awareness and the Bispectral Index (2008)

https://www.nejm.org/doi/full/10.1056/NEJMoa0707361

........................................

>Awareness during anesthesia: how sure can we be that the patient is sleeping indeed? (2009)

https://pmc.ncbi.nlm.nih.gov/articles/PMC2683150/

........................................

>Awake Under Anesthesia (2018)

https://www.newyorker.com/books/page-turner/are-we-all-awake...

https://archive.ph/t9T7o

........................................ >Single-trial classification of awareness state during anesthesia by measuring critical dynamics of global brain activity (2019)

https://www.nature.com/articles/s41598-019-41345-4

........................................

>Intraoperative and Anesthesia Awareness (2023)

https://www.ncbi.nlm.nih.gov/books/NBK582138/

MAC is the alveolar concentration (so strictly speaking defined only for anesthetic gases) at which half of people show no motor reaction on surgical incision. I understand your interpretation about paralysis, but we know the measurement endpoint is not paralysis in practice. Gases are hypnotics, and although they do cause some amount of muscle relaxation they do not induce paralysis. Hence the need for other drugs when we need paralysis. BTW, there is evidence that EEG prevents awareness under anesthesia, but it's not a guarantee either. Fortunately, awareness is extremely rare even in the select cases where it occurs more often (emergency C-section and cardiac surgery, especially in seniors).

Anesthesia gasses aren't paralytics. MAC is not about chemically preventing muscles from activating but depressing consciousness to the point that muscles don't move in reaction to painful stimulus. Chemically blocking muscle movement (neuromuscular blockade) takes an actual paralytic like succinylcholine. Pain control is yet another, separate factor. Even with depressed consciousness from a gas/propofol infusion and neuromuscular blockade, blood pressure (which is part of standard monitoring!) still will spike in response to painful stimuli. So usually, anesthesiologists will give an opioid in addition to gas/propofol to control pain, even if the patient isn't conscious and wouldn't be consciously aware of the pain of surgery.

The nightmare scenario you describe is when a patient has neuromuscular blockade, is not being given sufficient gas/propofol to depress consciousness, and has inadequate pain control that isn't being picked up in the blood pressure either because the anesthesia provider isn't paying attention or is controlling blood pressure through drugs to the point they can't see anything. If, for some reason, that kind of anesthetic is medically necessary, benzodiazepines can (if tolerated) prevent memories from forming lessening the chances of psychological trauma.

It obviously varies on place of practice and the way you were taught. My understanding is the evidence is pretty clear that it helps but happy to defer to your lived experience.

What about people who routinely use drugs in heavier concentrations or who have higher tolerance from genetics? How is that detected?

You just crank it up until those people don't react. With experience, you can anticipate those pretty well.

Reply on news.ycombinator.com