Inability to react caused by anasthetics does not necessarily turn off consciousness

Inability to react caused by anasthetics does not necessarily turn off consciousness

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During surgery, brains may be more in a drowsy state than suspected or even hoped for by patients

The expectation of patients undergoing surgery is, of course, that the anasthetics used for general anesthesia will not only prevent pain from occurring, but also provide for unconsciousness. In any case, we do not want to wake up suddenly and feel pain when we are under the surgical knife. At least that is the promise that comes with modern anesthetics.

However, it is still not clear exactly what effect they have. They influence the brain and somehow also temporarily switch off the sensation of pain along with consciousness. One consequence is that anesthesia interrupts memory. But exactly what consciousness is neurologically remains controversial. It is usually assumed that anesthetics block communication between brain areas. An alternative hypothesis is that brain areas are paralyzed and thus communicate less. The lack of information leads afterwards to unconsciousness and painlessness (effects of anesthesia by communication breakdown or low local information generation?).

Connection of pain and consciousness

However, the question remains whether pain is absent if there is no consciousness. However, this is assumed in animal protection, which only applies to vertebrates and above. This is stated in the German animal protection law: "A procedure involving pain may not be carried out on a vertebrate animal without deafness." And in Art. 17 states: "Whoever kills a vertebrate animal without reasonable cause or inflicts substantial pain or suffering or prolonged or repetitive substantial pain or suffering on a vertebrate animal out of cruelty shall be punished by imprisonment for not more than three years or a fine."

There are exceptions, however, in the case of young animals, of all things, which can be castrated or have their tails trimmed without deafness. In animal experiments, pain is said to be due to the "indispensable Mab" which is equivalent to a carte blanche. And with fish, also vertebrates, one is inclined for practical reasons to deny these a pain feeling, because they are supposed to have no cortex and thus no consciousness. Fish react to stimuli that can cause pain, but whether they feel pain is not sufficiently clear, according to a study on the subject (A fish does not feel pain). Perhaps also because they can not scream, but die silently on the hook or in the nets. In any case, the animal protection law has not been enforced so far, otherwise fishing would have to be banned.

When anesthetized, traumatic experiences and thoughts can pass through the mind

Finnish scientists at the University of Turku have now studied in humans whether anesthetics actually suppress pain and consciousness. The results were published in Anesthesiology and the British Journal of Anaesthesia. Not responding to stimuli, the scientists said, does not mean that a person is unconscious; one can have conscious experiences without showing behavioral responses. This also occurs during operations, but very rarely (0.1-0.2 percent). For their study, 23 subjects received a constant infusion of the sedative dexmedetomidine, which induces a sleep-like state that allows awakening, and 24 subjects received the stronger anasthetic propofol until they were no longer able to react. Then the dose was increased to induce unconsciousness.

The two agents have different sedative mechanisms of action and are used for surgery, propofol in addition with an opiod, as it does not eliminate pain. After 25 minutes of sedation, the subjects were awakened by calling their names twice and shaking their shoulders, and the activity in the brain was recorded by EEG. This was repeated again after another 25 minutes. The dose was then increased by 50 percent to cause unconsciousness. The scientists wanted to find out whether the effects of the drugs could be distinguished from the changes in the subjects’ state of consciousness. This is possible, they say, but it is still difficult to tell how deep the anesthesia goes during surgery.

18 subjects of the dexmedetomidine group (78%) and 10 of the propofol group (42%) could be awakened during the constant infusion, so they were not unresponsive. With increasing state of deafness, as is also known, the strength of delta waves (deep sleep) increased while beta waves decreased, frontal alpha waves were observed with both anasthetics, especially strong with propofol, associated with relaxation but not directly caused by the anasthetics. Delta and alpha waves were interrupted on awakening.

Subjects were able to recall waking up later, almost all of them reported dreamlike experiences mixed with reality. During anesthesia, in order to test the reactivity of the subjects in both groups, they were presented with semantically normal sentences as well as sentences with surprising endings, such as: "The night sky was full of shimmering tomatoes." If they hoard the sentences, they should print a lever whether the sentence makes semantic sense or not. Inability to react was when there was no answer to all 10 sentences.

When anesthetized, people are unable to distinguish between normal and strange sentences. When conscious, the brain reacts to unexpected words; under dexmedetomidine, a similar reaction occurred with the normal sentences. After the end of anesthesia all subjects could not remember the sentences. In addition, the test subjects were played unpleasant noises during the anesthesia. After waking up, they reacted more strongly to these sounds than to new ones. The scientists conclude from these results that the brain can process words and sounds even if the person does not remember them afterwards. Anasthesia does not require a complete loss of consciousness, but it is sufficient to separate the patient from his environment.

Do you have to worry about feeling something or even pain during an operation, even if you can’t remember it afterwards?? Scientists do not say this, but they do say that consciousness does not necessarily disappear completely during anesthesia, even if the person no longer reacts to his environment. During anasthesia, which is more like a deep natural sleep, in which the brain also unconsciously observes stimuli in the environment, dreamlike experiences and thoughts can still happen, the brain can even register language and try to understand words, "but the person will not consciously understand or remember them, and the brain cannot form complete sentences from them".

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