An Introduction to Anaesthesia


Anaesthesia is the practice of administering drugs to make patients insensitive to pain before surgery is carried out. Anaesthesia results in the loss of sensation, with or without the loss of consciousness. The first painless operation is thought to have been performed in 1842 by Crawford Long who used diethyl ether as an anaesthetic. There are two types of anaesthetics: local anaesthetics (used in epidurals during surgery or childbirth etc) and general anaesthetics (which limit physiological responses to surgical cuts, keeping heart rate, blood pressure and the release of stress hormones constant during the procedure).

The ancestor of modern-day anaesthetics is thought to be cocaine- for example, cocaine was used to treat toothache in the late 1800s. Cocaine is the only naturally occurring local anaesthetic ; other anaesthetics are derived synthetically. Cocaine, however, is not readily used as an anaesthetic because it can cause psychological dependence (i.e. drug addiction) and can be highly stimulating to the cardiovascular system. Instead, novocaine, lidocaine and tetracaine are used, which are all synthetic anaesthetics.
N.B: The listed anaesthetics all end in the suffix “aine” due to being chemically similar to cocaine.

How does an anaesthetic work?
The mystery behind anaesthetics is the fact that a variety of chemicals can result in the loss of consciousness. The basic understanding is that drugs work by binding to receptor molecules (just as a lock fits a key) but there is a long list of anaesthetics which range from large, complex molecules such as steroids to the inert gas xenon, which exists as atoms. The question begs, how can they all fit the same lock?
When it was found out that there was a relationship between the strength of anaesthetics and how well they dissolved in olive oil, scientists used the popular lipid theory to suggest that instead of binding to specific protein receptors, the anaesthetic physically disrupted the fatty membranes of nerve cells so that the nerve cells couldn’t work properly. However, test-tube experiments suggested that anaesthetics could bind to proteins in the absence of cell membranes. This led to the assumption that the solubility of anaesthetics in oil affected how easily they reached protein receptors.
Scientists believe that they have found an explanation for how local anaesthetics work. Local anaesthetics block the nerves that connect to a particular region in the brain to prevent the transmission of pain signals along those nerves. These anaesthetics work by moving into nerve cells and binding to sodium channels, blocking the influx of sodium ions. Local anaesthetics  are broken down readily by the body’s defence mechanisms, meaning that the drugs don’t stay in the body for very long for any associated symptoms to persist after the surgery.

Scientists are less sure about how general anaesthetics work. It has been suggested that general anaesthetics dissolve some of the fat found in brain cells and change the cells’ activities. The precise mechanisms are not known. However, a study using propofol, a general anaesthetic, found that the drug did something more significant to the patients’ brains than simply put them to sleep. 

Researchers at the University of Queensland found that propofol inhibited the movement of a key protein- syntaxin1A- needed at the synapses of all neurons, which resulted in decreased communication between neurons in the brain. From this study, we may argue that propofol affects the communication between neurons across the entire brain in a systematic way which differs from just being asleep. To some extent, this discovery also explains why people tend to be confused and groggy after an operation and why certain members of the population are vulnerable to anaesthetics (including children whose brains are still developing and people with Alzheimer’s/Parkinson’s disease).

Negative consequences of using anaesthesia:
Prior to administering anaesthetics, doctors conduct a pre-surgery assessment, which takes into account patients' BMIs, medical histories, current medications and ages. They will also have to consider potential risk factors associated with anaesthesia including emergency surgery, cesarean section, daily alcohol use and anesthesiologist error. The anaesthetist must then find out the optimum dosage for the patient: if an inadequate amount of anaesthetic is used, it will leave a patient aware of pain; an excessive amount will kill the patient. Ultimately, this procedure is tough because “consciousness is not something we can measure”.

If the correct dosage of anaesthetic is not used, the patient will experience side-effects which include a dramatic increase in blood pressure, heart attack, stroke, pneumonia and unintended intraoperative awareness. Perhaps the least known side-effect is unintended intraoperative awareness, which refers to the fact that some patients are aware of pain during an operation- even though an anaesthetic should have removed all sensation. Since muscle relaxants are given alongside anaesthetics, patients are not able to alert medics that they are still aware of pain and so, patients can go on to suffer long-term psychological problems after their operations.

By Kumaran Rajaratnam

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