The Networking World Anesthesia Convention (NWAC) takes place next week in Vancouver, BC, bringing together clinicians and researchers working in this vital medical field. It is worth remembering that without adequate anesthesia, modern medicine and surgery would be stuck in the quick and dirty field of “getting it over with fast”: read Fanny Burney’s account of a conscious mastectomy to get a feel for uncensored steel (note: not for the faint of heart).
Quite simply put, anesthesia makes a lot of modern medicine possible. From regional or local to full-immersion general anesthesia, the power of the drugs and the skill of the anesthetist smooth the way for both patient and clinician.
But how does it work—how does anesthesia take the unpleasantness away?
Local anesthetics, the ones used to freeze a patch of skin or gum, or injected around the spinal cord as an epidural, act on nerve conduction by interfering with ion channels. Without sensory nerve transmission, there is no painful sensation of being cut, poked, prodded or gouged.
However, general anesthesia is different. Not only does it take away the pain, but it also knocks the patient out so effectively that they have no memory of the procedure when they wake up.1 And it does all this without turning off the areas of the brain that maintain vital functions such as respiration and circulation.2
The best general anesthetics, either volatile gas for inhalation or injectable agents, tend to be highly fat-soluble, suggesting that they act via the cell membrane, a lipid-rich environment. There is a whole slew of pharmacokinetic data on these agents, mostly pointing to altered neurotransmitter release in the brain, with a side serving of interaction with protein receptors. But it doesn’t explain completely how they induce unconsciousness or stop memories from being made.
Currently, neuroscience has not identified a discrete site within the brain that controls consciousness; there is no simple switch for on or off. Instead, neuroscientists think that consciousness is a widespread phenomenon, explained by a global workspace theory. In this model, the different signals evoked within the brain from external and internal stimuli integrate into a working memory and central processing unit.
The global workspace pulls everything that is happening—real, imaginary and abstract—together, so that we can not only respond to the environment but also draw on memories to interpret events, conjecture and predict into the future. It’s how we can simultaneously look at a bunch of tulips, remember how nice it was the last time someone brought us a bunch of flowers and perhaps plot how to guilt them into buying again. Or chocolates. (Or both…)
Since general anesthetics prevent the propagation of signalling around the brain, researchers think that maybe this is how they switch off consciousness. But they aren’t sure.
Although the pharmacokinetic investigations continue, what’s important to note is that practising clinicians come together at conferences such as NWAC to learn more about safe and effective practice. This way, when you next slip under the influence, you can concentrate on how you’re in safe hands, and you won’t be thinking, “My anesthetist doesn’t know how this works!”…will you?
Networking World Anesthesia Convention (NWAC)
Apr 29–May 2 at the Vancouver Convention Centre
Further reading:
- Ku, Seung-Woo, UnCheol Lee , Gyu-Jeong Noh, In-Gu Jun, and George A. Mashour. 2011. “Preferential Inhibition of Frontal-to-Parietal Feedback Connectivity Is a Neurophysiologic Correlate of General Anesthesia in Surgical Patients.” PLoS ONE 6(10): e25155. doi:10.1371/journal.pone.0025155.
- Noirhomme, Quentin, Andrea Soddu, Rémy Lehembre, Audrey Vanhaudenhuyse, Pierre Boveroux, Mélanie Boly, and Steven Laureys. 2010 “Brain Connectivity in Pathological and Pharmacological Coma.” Frontiers in Systems Neuroscience.
doi:10.3389/fnsys.2010.00160. - Perkins, Bill. 2005. “How Does Anesthesia Work?” Scientific American.
[1] In the best-case scenario, the patient has no recollection of events while under general anesthesia. However, a tiny proportion of people do experience accidental awareness during general anesthesia. Conference delegates will have the opportunity to find out what UK anesthetists learned during a national audit into this phenomenon.
[2] Of course, this is where the skill of the anesthetist comes in, to prevent overdose suppressing these vital functions.