For over 150 years, doctors have relied on anaesthetics to sedate patients while performing invasive surgery. The feat was first performed by William T. G. Morton in 1846 and has been commonplace in hospitals ever since. That said, while anaesthetics will usually knock a patient out cold, there is a chance they could wake up while under the knife.
Cases of anaesthetic awareness are extremely rare, with experts estimating that just 0.005% of patients experience a state of consciousness. New research published in the journal Anesthesiology explores the concept further and suggests that while anaesthetised patients may not be completely alert, their brains aren't entirely comatose. Instead, they slip into a "sleeping state" that can actively dream, process thoughts and react to external stimuli.
"The state of consciousness induced by anaesthetics can be similar to natural sleep. While sleeping, people dream and the brain observes the occurrences and stimuli in their environment subconsciously," explains Antti Revonsuo, a psychology professor at Finland's University of Turku.
Sleeping vs sedated
To explore the brain's capacity for consciousness while anaesthetised Revonsuo and his team analysed electrical activity changes in the brain of healthy volunteers. They used a mix of dexmedetomidine and propofol, two commonly used sedatives, to lull the patients into an unresponsive state. While sedated, the volunteers were played a series of pre-recorded sentences, including peculiar statements like "The night sky was filled with shimmering tomatoes." The researchers noted that while the irrational sentences were noticed by the brain during the electroencephalograms, the information wasn't retained.
"The responses in the EEG showed that the brain cannot differentiate between normal and bizarre sentences when under anaesthesia," says Katja Valli, a fellow Turku professor. "When we used dexmedetomidine, also the expected words created a significant response, meaning that the brain was trying to interpret the meaning of the words. However, after the participants woke from the anaesthesia, they did not remember the sentences they had heard and the results were the same with both drugs."
So, while the brain doesn't slip into a full state of unconsciousness while under the influence of anaesthesia, it doesn't feel pain or actively record the experience which makes drugs like dexmedetomidine and propofol perfectly suitable for surgery.
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