Can we exactly explain consciousness modifications during general anesthesia?
I am not an anesthesiologist however I am a student of consciousness. Our thalamus perceives the consciousness via tonically active state when we are awake. During tonically active state cortex and peripheral sensory information is processed by thalamus and we can experience consciousness . However during anesthesia the tonically active state is replaced by slower waves called oscillatory rhythm that functionally disconnect the thalamus. Since this rhythm can alternate between tonic rhythm during incomplete anesthesia , the fluctuation in consciousness can occur even with eyes closed.
Good morning,
I concur with Ravinder's excellent answer above. There is a degree of fluctuation in electromotive forces that reflect (imperfectly) the very difficult to measure concept of consciousness. We used a bispectral index monitor to maintain levels of hypnosis during a research study, and found that it was no easy task to maintain some set level of neural activity. Induction of anesthesia with propofol alone produced a distinct drop in BIS, followed by a rapid return to preinjection levels. The simple addition of a small amount of lidocaine to the mix (to decrease the painful sensation associated with propofol injection) resulted in a much flatter recovery curve, reflecting decreased electromotive force within the neurons. From the viewpoint of clinical practice, anesthetics must be adjusted throughout the course of the surgery as stimuli (incision, closure and so on) wax and wane.
I am attaching four articles which might be of interest to you and provide some background. One is Hamerhoff's nature of consciousness, the next two deal with recall and sleep compared to anesthesia, and the last is our small research project on implicit memory formation and discusses the BIS monitor a bit...hope this helps.
Thanks for the interesting question!
Best wishes,
Rich
It is the Spirit behind the mind that makes the mind conscious. When the mind disconnects from the Spirit as explained by Ravinder Jerath, it becomes unconscious. General anesthesia is a forced separation of Spirit and mind. But there are people who can separate themselves from their mind by act of will. Such is the case when person is in samadhi (trance). You can notice such fluctuation of consciousness in the life of Sri Ramakrishna. I suggest following books.
"Sri Ramakrisha The Great Master" by Swami Saradananda, (tr.) Swami Jagadananda, Sri Ramakrishna Math, Madras; and "The Gospel of Sri Ramakrishna." by Mahendranath Gupta, (tr.) Swami Nikhilananda, Ramakrishna-Vivekananda Center, New York.
Above books available across the world at Vedanta Society bookstores. Links to Vedanta Centers Online:
http://www.vedanta.org/wiv/links/centers.html
My humble philosophical take on this matter is as follows: There is no EXACT!!
Consciousness requires as described above a neurochemically medicated system to reverberate based on inputs from the external and internal environment. (the physical metaphor is the "resonant frequency" and its response to a driving frequency and a damping agent).
The more complex the system the easier it is to interrupt, and move away from the "resonant frequency". The mind is clearly a VERY complex system thus the action of drugs need not be very significant to disrupt the most complex functions (i.e. conciseness, memory etc). At higher doses the more basic networks can be disrupted and thus we observe for example, respiratory cessation (apnoea).
BIS as described above measures the disruption of what I call the "resonant frequency of consciousness" and describes it in terms of "disorder". More disorder= more conscious (more networks reverberating), less disorder= less conscious.
Not sure if that helps or hinders!! Good luck!
For me as an anaesthetist, it is very much a question of a balance between sensory input from the surgical stimulation and the level of intoxication from the anaesthetics. Thus, during periods of intense stimulation, of which laryngoscopy and endotracheal intubation is the worst, followed by skin incision, the level of intoxication must be deep = high concentrations of anaesthetics at the effect site, whereas during low intense stimulation, best exemplified by skin suturing, the concentration of anaesthetics should be low. Even though we have quite good drugs available today = short acting and thereby quite steerable, they are not that good, as we would like them to be. Therefore, we must aim for some margin. Moreover, it is not only a matter of variation in stimulation for a specific patient during his/her surgical procedure. Another problem is the huge inter-individual variation in drug demand in a population for the same intensity of surgical stimulation. Quite challenging, I must say. There are numerous papers about awareness in literature. Search for general anaesthesia and awareness and you will get hundreds of papers, if not a thousand.