Sweet anaesthesia and the mystery of consciousness

Discover Magazine has an excellent article on the science of anaesthesia and why doctors need to struggle with the problem of consciousness to make someone comfortably numb.

If you’re not familiar some of the mysteries of anaesthesia, you may be surprised to know that we don’t actually know how most anaesthetics work and we have no reliable way of telling whether someone is unconscious.

This is important because general anaesthesia usually involves two types of drug, muscle relaxants and hypnotics. It’s possible that the muscle relaxants have their paralysing effect but the hypnotics don’t fully work, so you’re awake and aware, but don’t respond when you’re touched or talked to.

Hence anaesthetists would love a device which says whether someone is concious or not, but unfortunately, divining consciousness from the brain is one of the hardest problems in science. So, they’ve come up with various other methods:

Sometimes the anesthesiologist will use a blood pressure cuff on a patient’s arm to block the muscle relaxants in the bloodstream. Then the doctor asks the patient to squeeze a hand.

This sort of test can distinguish between a patient who is awake and one who is out cold. But at the borderline of consciousness, it is not very precise. The inability to raise your hand, for example, doesn’t necessarily mean that you are unconscious. Even a light dose of anesthesia can interfere with your capacity to keep new pieces of information in your brain, so you may not respond to a command because you immediately forgot what you were going to do. On the other hand, squeezing an anesthesiologist’s hand may not mean you’re wide awake. Some patients who can squeeze a hand will later have no memory of being aware.

Seeking a more reliable measuring stick, some researchers have started measuring brain waves. When you are awake, your brain produces fast, small waves of electrical activity. When you are under total anesthesia, your brain waves become deep and slow. If you get enough of certain anesthetics, your brain waves eventually go flat. Most anesthesiologists monitor their patients using a machine known as a bispectral index monitor, which reads brain waves from electrodes on a patient’s scalp and produces a score from 100 to 0. But these machines aren’t precise either. Sometimes patients who register as unconscious can still squeeze a hand on command.

The article then goes on to discuss some fascinating neuroscience studies that use anaesthesia to try and understand what changes in the brain as someone slips into unconsciousness.

It’s a great read and an interesting look into what you might called ‘applied consciousness research’.

Link to ‘Could a Dose of Ether Contain the Secret to Consciousness?’