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Scientists Uncover More About Anesthetic

Scientists Uncover More About Anesthetic

Scientists beginning to understand more about how anesthetic works…

Anesthetics are considered routine when it comes to visiting the dentist, but despite the regular application of such a practice scientists are only just beginning to understand how anesthetics really affect the brain and body.

Anesthetics were first discovered in the 18th century when a chemist named Humphry Davy stumbled upon the sedative effects of laughing gas. Davy shared the gas with a distinguished group of friends including Samuel Taylor Coleridge, James Watt, and Robert Southen, and these trails laid the foundation for the medical application of anesthetics.

The common view maintains that going under (induction) and coming back up (emergence) are the same process, just in reverse.

However researchers, led by Dr. Max Kelz at the University of Pennsylvania School of Medicine, observed that each process is in fact different.

us hospital corpsman performs local anesthetic

Scientists Uncover More About Anesthetic

Image Credit: U.S. Navy, 2010.

To explain these observations, the researchers have introduced a concept they call “neural inertia. Neural Inertia refers to the brain’s resistance to transitions between consciousness and unconsciousness, and figuring how exactly how it works could give provide a better understanding of the different states of consciousness, including comas and vegetative states.

According the current model, when anesthetic drugs reach the central nervous system the patient become unconscious. Over time the anesthetic slowly passes through the system and the patient wakes up. However, if this were true then the concentrations of anesthetic should be the same at induction and emergence.

Researchers realized they could easily test this theory by measuring the concentration of anesthetic in the brain when going under, and coming back from the anesthetized state.

Tests on fruit flies showed that levels of anesthetic were higher at emergence than when entering the anesthetized state, which indicates a delay in, or resistance to, returning to the waking state.

Observations in humans also provide some evidence for neural inertia. Patients with narcolepsy with cataplexy – a sleep disorder that causes intense daytime sleepiness and sudden losses of muscle tone – can take as long as 8 hours to emerge from general anesthetic, whereas typical patients take only minutes.

Narcolepsy with cataplexy is caused by reduced mounts of a protein called hypocretin, which help regulate wakefulness and REM sleep. Taking this knowledge, scientists performed a separate experiment on mice with mutations in the hypocretin gene causing sleep disorders similar to humans with narcolepsy. The mice also showed a delay in emerging from unconsciousness, but no difference entering into the anesthetized state. This indicates that only emergence is dependent on the hypocretin system.

A small percentage of patients report experiencing awareness during surgery—estimates are low (around 1 in 1000 cases). On the other end of the spectrum, patients with certain neurological conditions may not wake up for an extended period after general anesthesia. Researchers like anesthesiologist, Dr. Kelz hopes that the recent finding will led to understanding the key to neural inertia, and ultimately develop better anesthetics tailored to specific patients.

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  1. Stephen Dougherty: What Doctors Don’t Understand about Anesthesia. Scientific America, 28/02/2012.

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