Dear Dani Sandelin

At first, I appreciate your curiosity.

In simple sentence, our brain has different types of cells and nuclei and feedback system for arousal and sleep (Hypothesis of “flip-flop” mechanism of sleep–wake cycles).

There is also differential response to the anesthesia drugs by different cells of the brain within the person and even inter person variation is there.

The anesthesia dose is usually calculated for 50% population which is then adjusted for 3 standard deviation to maintain anesthesia, which itself can not give 100% guarantee that entire population will be responding with that dose.

Many a time, anesthesiologists needs to awake, reduce dose for inherent properties of the surgical plan and procedure.

I feel you can go through the following article which will help you

Article Intraoperative Awareness From Neurobiology to Clinical Practice

Article Intraoperative awareness: Controversies and non-controversies

Article General Anesthesia: A Probe to Explore Consciousness

Thank you very much. If you are planning a research...please let us know your experience and results

Dear Habib Md Reazaul Karim thank you so much for your thorough and detailed answer and recommended articles! I find this topic very interesting indeed. It would certainly be interesting to conduct a meta-analysis on this topic!

Habib Md Reazaul Karim would also be interesting to research more about

post operative cognitive alterations after an anesthetic procedure, both long term effects (if any) as well as immediately upon awakening.

Dear Habib Md Reazaul Karim ,

being one of the fathers of end-tidal controlled inhalation anesthesia in the real closed system I like to respond:

a. The system described above manages the end-tidal level of a volatile agent within 10% of the set value. In this way the effect of an undesired low level of an volatile agent will be prevented, possible cause.

b. During events with blood loss, it was noticed that the system injected agent to compensate for the diluted blood of the loss was compensated, so the end-tidal level remains constant.

c. the human variety will effect the level of and tidal agent required, once the right level has been found that level will be kept.

It will be valid for the method mentioned.

Applying a charcoal filter the agent may be washed out to a lower level set.

Dear Bart Westerkamp

Thank you very much for your response and insight. I can see your work in the field of closed loop anesthesia (I hope it is 100% servo controlled-not partial), and applaud your works. While we may assume that your system will keep end-tidal concentration and blood concentration stable during different situations, the impact of this system on reduction of awareness will be interesting to know and evaluate in the future. As, you system too depends on the end-tidal concentration values, which are actually derived from previous study, I believe it may be able to reduce the awareness attributed to human and clinical clinical factors, but probably not for inherent limitations of end-tidal concentration in context to different response by different population to the same end-tidal concentration value. After all one size can not fit in entire population of the world. So, variation in the response is expected.

Once again I congratulate you for the contribution in the field.

Thank you

Patients who take psychiatry medications have much more chance for awakeness during anesthesia. The point is in polarization of brain of cell membranes and their higher level for potencials. That can result with higher doses of anesthetics for the same effect. That because, using of BIS as the deep of anesthesia is absolutely irrelevant. It is known that many of patients with BIS value of 60% or less could be awake , and on the other side, many of patients with BIS value of 60% or higher could be anestesized. Electrical potential of cell membrane in brain is one of the answers.

Thank you Nikola Bradic for your response! This is very helpful. Interesting to know that psychiatric medications can have this effect during anesthesia.

There are simple and practical reasons why intraoperative awareness occurs.

In short procedures such as gastroscopies and/or colonoscopies, bolus doses of propofol rather than continuous infusions, are sometimes given due to convenience. This results in inconsistent effect site concentration of propofol, resulting in awareness.

In cardiac or trauma procedures, "narcotic anaesthesia" is traditionally used to prevent falls in blood pressure. This means that little or no agents are used during induction/maintenance of anaesthesia other than narcotics and muscle relaxants.

Intraoperative awareness also occurs as a result of sub-optimal titration or early termination of intravenous propofol during procedures.

For the majority of routine cases general anaesthesia can be administered without muscle relaxants. In these cases if the anaesthesia lightens the patient may subconsciously move. The patient will not experience awareness if the anaesthetist then deepens anaesthesia.

If a muscle relaxant has been given then this very obvious sign of lightening anaesthesia is missed. So when muscle relaxants are administered the risk of awareness is increased. In my personal practice I minimise the use of muscle relaxants during anaesthesia.