Tuesday, September 19, 2006

Consciousness - What Little We Know

Recent study in the journal Science:

Functional MRI imaging of a 23 year old vegetative woman shows that her brain still "lights" up in patterns that are similar to normal brains. The scientists tested whether her damaged brain could process speech, and the appropriate brain areas showed activity. She was asked to imagine playing tennis, and the motor areas of the brain showed activity.

What does this mean? That she could hear the physicians? That her brain was still processing commands? That although she was unconscious, her basic brain functions were still intact?

Medicine doesn't really know much about "consciousness." This brings up a memory from medical school. During the anesthesia rotation, one of the attendings was testing the Bispectral index (BIS), then a novel method of measuring the level of a patient's awareness under general anesthesia.

First, the background on BIS: This type of machine came about because of the rare but horrible stories of patients being under general anesthesia but feeling every bit of the procedure. General anesthesia has many purposes, including pain relief, which usually comes from being "unconscious," and sometimes paralysis of the entire body, for special surgical procedures. If someone is paralyzed with medications, but the pain relief is inadequate, there is the potential that they can feel the entire surgical procedure, but can't say a thing or even get out of the way of the scalpel. So basically they're operated on without any anesthesia, but the surgeon and anesthesiologists don't have a clue. Not a pleasant thought. So at the time, the BIS was this new device that was marketed as being able to measure the level of consciousness/awareness of a patient who was unable to communicate with the physician (eg while under general anesthesia). The machine worked by real-time and continuous electroencephalographic (EEG) analysis and generated a dynamic score ranging from 0 (deep anesthesia) to 100 (awake). Target goal for surgical anesthesia was around 40 to 60.

The anesthesia attendings were trying this non-invasive device on patients undergoing regular surgical procedures, and realized that it was pretty interesting and potentially very useful. Well, one of the attendings decided to try the device on a "brain dead" organ donor. (ie people who are in traumas who suffer irreversible brain damage, but wanted to donate their organs if the opportunity ever arose.) These organ donors have to "pass" a rigorous evaluation by two physicians to ensure that they are truly brain dead. This involves many tests of brain function, including shutting off the ventilator that they are on, and documenting that their brain stem no longer functions - which manifests in one way as a failure to breathe on their own. If they prove to be medically brain dead, the organ donation process may proceed. The process involves keeping the patient alive by the use of the ventilator and other machines, until the time of the organ harvest. When that time comes, the patient is taken to the OR and the organs of interest are "harvested" - taken out of the donor body and packed on ice for delivery to the recipient. The donor body is then closed and disconnected from the machines, and the donor formally passes away.

One would think that a brain dead person, one who cannot even breathe on their own, would not score very high on a BIS score. Unfortunately, they are also not at zero. The attending never told me what the score exactly was, but he did say that after using the machine on one organ donor, and seeing it rise with the scalpel incsions, he got the heebie-jeebies and had to disconnect the BIS. He never used it again in that scenario.

What does this mean? How can someone who is brain dead, who will die as soon as the ventilator is shut off, still have brain waves? Or still respond to external stimuli? What is the relationship of consciousness to the body, and how come there is so little understanding of this area?

* picture taken in lush Kaua'i

3 Comments:

Anonymous Anonymous said...

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8:34 AM  
Anonymous RDoc about Heart problem said...

I read a study about brain waves - it is possible to evoke the brain waves in the cut off head of rabbit in the lab 1 hour after the cutting it off by apllying some external electromagnetic irradiation. Does it really mean that the animal is still alive (those brain waves look like in an alive one).

If it is so, does it mean we can revive a person 1 hour after death.

Or maybe intact brain waves mean something else?

6:53 AM  
Anonymous David Harmon said...

Put it this way... would you be astonished to find a high BIS from somone with a damage to the brain stem itself, such that they were paralyzed and unable to breathe, but otherwise aware? Remember too, that normally sleeping people are commonly responsive to sound, touch, and sometimes light.

It seems perfectly reasonable to me that someone might have a fair bit of "higher" function available and reacting to stimuli, but nevertheless be locked into coma, and unable to self-sustain. Of course, that wouldn't particularly mean that it was possible to "save" them, as the damage involved could still be irreparable!

The decision to "harvest" organs is fundamentally a difficult ethical decision, and I wouldn't expect it to get easier just because of better sensors.

4:09 PM  

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