Slipping Into Unconsciousness: General Anesthesia in the Vulnerable, Concussed Brain

Most of the focus surrounding the outcomes and use of general anesthesia has been on two populations – pediatric patients and elderly patients. This is due to the vulnerability of the young, developing brain and the aging brain. In an article titled “The Hidden Dangers of Going Under,” it is posed that the negative effects of general anesthesia in older adults may be due to the binding targets of the drug to the surface proteins of neurons in the brain which decrease in abundance with age. Input from experts suggests that the brain in an older adult may have a difficult time lighting up the connections within the brain that may have broken down under general anesthesia. 

What does this mean for the vulnerable, concussed or post-concussed brain in which there is already poor circuitry and difficulty lighting up connections? The very anesthetics used do such a great job because they incapacitate the surface proteins of neurons that are responsible for regulating attention, memory, learning and sleep. 

“Although physicians have known about the possibility of such confusion since at least the 1980s, they had decided, based on the then available evidence, that the drugs used to anesthetize a patient in the first place were unlikely to be responsible. Instead, they concluded, the condition occurred more often because of the stress of surgery, which might in turn unmask an underlying brain defect or the early stages of dementia. Studies in the past four years have cast doubt on that assumption, however, and suggest that a high enough dose of anesthesia can in fact raise the risk of delirium after surgery. Recent studies also indicate that the condition may be more pernicious than previously realized: even if the confusion dissipates, attention and memory can languish for months and, in some cases, years.”1

Because of so many variables and factors that go into surgery, scientists have struggled to point out causality between anesthesia and poor outcomes and symptoms. Anesthesia is only a piece of the puzzle and with so many compounding factors, can it truly be the culprit for worsening of preoperative symptoms in the concussed patient? I am going to address some of these components.

Are the negative effects of anesthesia dose dependent?

As research continues to be published on this topic, the amount of anesthesia given is being evaluated and considered. Is there a greater risk the deeper someone slips into unconsciousness?

Using EEG, we finally have more information as to what happens to the brain under anesthesia. EEG (electroencephalography) is similar to an EKG of the heart but measures the electrical activity of the brain. Most anesthesiologists do not monitor brain activity during surgery, though one anesthesiologist holds a strong stance on this topic and believes every patient’s brain should be monitored during surgery. Neuroscientist and anesthesiologist, Emery Brown, monitors all of his patients in surgery via EEG and believes this should be common practice. This way, the dosing of anesthesia can be very individualized and adjusted precisely for each patient.2,3

You can imagine that your neurons are constantly firing and communicating with each other as you think, move, talk, assess your environment and surroundings. One of the most common anesthetics used today, propofol, shuts down these neurons within seconds of administration. The communicating and firing throughout your brain comes to a halt. The frequency of neurons in an awake, healthy brain spike approximately 10 times per second. After the initiation of the anesthetic, those spikes drop to once per second or even less.The fewer electrical spikes throughout the brain means the deeper the anesthesia which is where EEG monitoring comes into play. By viewing real time activity of the brain, the anesthesia dose can be adjusted accordingly per patient.

A study was conducted in Hong Kong in 2013, assessing the outcomes of patients receiving general anesthesia with one group monitored via EEG to keep the brain’s electrical activity as high as possible and the other group monitored via heart rate and blood pressure only. 462 of the patients were in the EEG group and 459 in the other. 16% of the patients who received light anesthesia based on EEG monitoring, displayed confusion postoperatively as compared to 24% of the patients in the standard of care group. Looking at long term outcomes, 15% of patients who received standard of care anesthesia experienced lingering mental setbacks for at least three months compared to 10% in the EEG group.1

It seems EEG monitoring of patients in surgery should become standard of care and could aid in preventing some of these long-lasting, poor outcomes. 

Would regional anesthesia be better for the concussed patient than general?

What if instead of general anesthesia they used a regional block with conscious sedation? Could this potentially protect the brain from the negative effects of general anesthesia?

Regional anesthesia uses local anesthetics to block a nerve of a large area. Conscious sedation is often used with it as a way to offer a comfortable environment for the patient without them completely losing consciousness. The goal of conscious sedation is to make you feel relaxed; you may feel drowsy or loopy. For instance, a patient may undergo hand surgery by having a nerve blocked in the upper arm or wrist in combination with conscious sedation. In theory, this sounds like a better bet for concussed patients. They can perhaps avoid the incapacitation of neuron communication, potential fluctuations in blood pressure and blood flow to the brain. 

The bonus of this is that the patient can undergo a procedure or surgery without losing consciousness and can avoid some of the negatives of general anesthesia. Although, is this always the case?

Anesthesiologist, Frederick Sieber, conducted a study comparing delirium in patients receiving regional versus general anesthesia. All patients were undergoing surgery for hip fractures and were 65 and older. The regional anesthesia group received propofol for conscious sedation and an anesthetic to numb the nerves coming from the spinal cord. The depth of anesthesia achieved was monitored via the standard of care with heart rate and blood pressure. Simultaneously, a computer which Sieber and his team could not see, was monitoring the electrical activity of a patient’s brain using electrodes on the forehead. Sieber was astonished at what he saw. He found that “Eighty-seven percent of patients’ brain activity dipped low enough to qualify as general anesthesia during at least part of the surgery.” Based on this, he suspects it is “common for patients getting regional anesthesia to receive so much sedative drug that they are actually in a state of general anesthesia.”1

Without EEG monitoring of the brain and using the current standard of care monitoring of heart rate and blood pressure, patients may receive so much sedative that they end up in a state of general anesthesia anyway. This is also something to consider in the concussed patient. For me personally, I had thought choosing regional over general would erase all of the concerns but as this shows, the result may just be the same.

Part III

Discussed next are other important factors to consider: the stress of surgery itself, site of surgery, inflammation produced by surgery and if the effects of anesthesia on the brain are completely reversible.


1. The Hidden Dangers of Going Under 
2. This is your brain under anesthesia
3. General Anesthesia Causes Telltale Brain Activity Patterns

2 thoughts on “Slipping Into Unconsciousness: General Anesthesia in the Vulnerable, Concussed Brain

  1. So very interesting and beneficial to read especially for a non-medical person as I!!! Always wondered about the pros and cons of the external manipulations of brain functions to withstand pain!

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