How does Anaesthesia Actually Work?

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Anaesthesia is a very unusual phenomenon which although incredibly useful in modern medicine, has not been understood very well up until recently. However, now with new information being found about anaesthesia, that is all about to change.

First, it is good to have an understanding of the history of anaesthetics leading up to today. Until the 1700s, anaesthetics were mostly unreliable, and dangerous. For example, early anaesthetics involved people ingesting ethanol or using herbal mixtures. It is often thought that anaesthetics have to be chemicals which are breathed in, injected or drank. However, some patients were ‘knocked-out’ before an operation was performed on them. These first anaesthetics despite often ineffective, paved the way to the modern versions used today. Hypnosis, while controversial, was used as a form of anaesthetic in the 1700s as well, in susceptible individuals who are very rare in society. Finally, in the ‘Enlightenment’, in the late 18th century, the gases of carbon dioxide, oxygen and nitrous oxide were classified and able to be contained. These gases are the pillars of modern breathable anaesthetics. Also, the compression of nerves was shown to make parts of the body be numb. The famous surgeon John Hunter used this method to carry out an amputation, painlessly, but he was only able to do this once. In 1846, a successful painless experiment was carried out by William Morton using a strong mix of nitrous oxide with other chemicals, breathed in by a patient, while removing the patient’s tumour. This resulted in medical research focusing heavily on new, better anaesthetics. What followed in the anaesthesia field was mainly due to the experiment by Morton. For example, general anaesthetics were introduced into clinical practice, nitrous oxide anaesthetics were reinvented to be better, local anaesthesia was more common, and much more.

Even though there has been much innovation in the field of anaesthetics, not many scientists or doctors have really understood the science behind why they work, just that they do work and in most cases are safe for doctors to use. Until the mid-2010s, basically all scientists knew was that most anaesthetics worked by interrupting nerve signals occurring in your brain and the rest of your body. As nerve signals are suppressed in your body, pain is not processed or felt by the body and it is harder or impossible to remember your surgery, depending on the strength of the anaesthetic. However, the properties of anaesthetics that make this  incredible mechanism work have not been found still, but we now have better ideas as to the what types of properties of anaesthetics could cause their functionality to be so effective.1

New findings about anaesthesia revolve around sleeping patterns, how consciousness works, and how these factors interact. Research in these fields led to the “lipid hypothesis”, an old theory of how anaesthetics function, but more research in recent times, has led to better explanations of this theory. It is known that as the potency of an anaesthetic increases, the anaesthetic’s solubility in lipids increases. Not long ago, a proposed explanation for this was created. This explanation theorises that anaesthetics have chemical properties which allow them to produce lipid rafts (disruptions of heterogeneous lipid clusters) in lipid solutions. This stops ion channels in the body from opening, and so stopping neurones from carrying current. Furthermore, it has been noted that as the lipid rafts form, the enzyme PLD2, a fluorescent chemical, is released. This enzyme has been seen to activate molecules in other lipid clusters in the body, including the molecule TREK1, a potassium ion channel. As this ion channel is activated, neurones are “frozen”, which is why they can not temporarily carry current. Delving deeper into this logic, these TREK1 channels release potassium when activated, hyper-polarising the neurones, making the neurones lose their function for a controlled period of time. The result of this is the phenomenon anaesthesia. You may be thinking that the PLD2 enzyme is the reason for anaesthesia occurring, but further experiments on fruit flies showed that without PLD2, more anaesthetic was needed to reach the same level of unconsciousness, but the removal of this enzyme did not stop the anaesthetic properties of the chemicals from working.  As a side note, this information about the functionality of anaesthetics has given scientists more belief that lipids have a huge role in the generation of sleep, giving rise to more research to find the link between sleep generation and lipids in the body.2

Anaesthetics have come a long way from the basic, inefficient original forms to the painless, effective and safe modern ones. Until perhaps a few years ago, anaesthetics were one of the biggest sections of medicine poorly understood, but now with more research the “lipid hypothesis” has more support. However, as PLD2 is not the only mechanism at play with anaesthesia, the search is still on to find the other mechanisms at play which make this sensation occur.


References

  1. Bird, E., 2020. Scientists Unravel The Mystery Of Anesthesia. [online] Medicalnewstoday.com. Available at: <https://www.medicalnewstoday.com/articles/scientists-unravel-the-mystery-of-anesthesia#New-avenues-for-research> [Accessed 13 June 2020].
  2. Geddes, L., 2011. Banishing Consciousness: The Mystery Of Anaesthesia. [online] New Scientist. Available at: <https://www.newscientist.com/article/mg21228402-300-banishing-consciousness-the-mystery-of-anaesthesia/> [Accessed 13 June 2020].

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