[00:06] If you've had surgery,
[00:07] you might remember starting to count
backwards from ten,
[00:11] nine,
[00:12] eight,
[00:13] and then waking up with the surgery
already over before you even got to five.
[00:18] And it might seem like you were asleep,
but you weren't.
[00:21] You were under anesthesia,
[00:23] which is much more complicated.
[00:25] You were unconscious,
[00:26] but you also couldn't move,
[00:28] form memories,
[00:29] or, hopefully, feel pain.
[00:32] Without being able to block all those
processes at once,
[00:35] many surgeries would be 
way too traumatic to perform.
[00:39] Ancient medical texts from Egypt,
Asia and the Middle East
[00:42] all describe early anesthetics
[00:44] containing things like opium poppy,
[00:46] mandrake fruit,
[00:48] and alcohol.
[00:49] Today, anesthesiologists often combine
[00:52] regional, inhalational 
and intravenous agents
[00:56] to get the right balance for a surgery.
[00:58] Regional anesthesia blocks pain signals
from a specific part of the body
[01:03] from getting to the brain.
[01:04] Pain and other messages travel through
the nervous system as electrical impulses.
[01:10] Regional anesthetics work by setting up
an electrical barricade.
[01:14] They bind to the proteins 
in neurons' cell membranes
[01:18] that let charged particles in and out,
[01:20] and lock out positively charged particles.
[01:23] One compound that does this is cocaine,
[01:26] whose painkilling effects 
were discovered by accident
[01:29] when an ophthalmology intern
got some on his tongue.
[01:33] It's still occasionally used 
as an anesthetic,
[01:37] but many of the more common
regional anesthetics
[01:39] have a similar chemical structure
and work the same way.
[01:43] But for major surgeries where you need
to be unconscious,
[01:46] you'll want something that acts
on the entire nervous system,
[01:49] including the brain.
[01:51] That's what inhalational anesthetics do.
[01:54] In Western medicine, diethyl ether
was the first common one.
[01:58] It was best known as a recreational drug
[02:01] until doctors started to realize that
people sometimes didn't notice
[02:05] injuries they received 
under the influence.
[02:08] In the 1840s, they started sedating
patients with ether
[02:12] during dental extractions and surgeries.
[02:15] Nitrous oxide became popular
in the decades that followed
[02:19] and is still used today.
[02:20] although ether derivatives, 
like sevoflurane, are more common.
[02:25] Inhalational anesthesia is usually 
supplemented with intravenous anesthesia,
[02:30] which was developed in the 1870s.
[02:32] Common intravenous agents include
sedatives, like propofol,
[02:36] which induce unconsciousness,
[02:37] and opioids, like fentanyl, 
which reduce pain.
[02:42] These general anesthetics 
also seem to work
[02:44] by affecting electrical signals
in the nervous system.
[02:47] Normally, the brain's electrical signals
are a chaotic chorus
[02:51] as different parts of the brain
communicate with each other.
[02:55] That connectivity keeps you awake
and aware.
[02:58] But as someone becomes anesthetized,
[03:00] those signals become calmer
and more organized,
[03:03] suggesting that different 
parts of the brain
[03:05] aren't talking to each other anymore.
[03:08] There's a lot we still don't know
about exactly how this happens.
[03:12] Several common anesthetics bind to
the GABA-A receptor in the brain's neurons.
[03:18] They hold the gateway open,
[03:20] letting negatively charged particles
flow into the cell.
[03:25] Negative charge builds up
and acts like a log jam,
[03:28] keeping the neuron from transmitting
electrical signals.
[03:31] The nervous system has lots
of these gated channels,
[03:35] controlling pathways for movement,
[03:37] memory,
[03:38] and consciousness.
[03:39] Most anesthetics probably 
act on more than one,
[03:42] and they don't act on 
just the nervous system.
[03:45] Many anesthetics also affect the heart,
[03:47] lungs,
[03:48] and other vital organs.
[03:50] Just like early anesthetics,
[03:52] which included familiar poisons like
hemlock and aconite,
[03:55] modern drugs can 
have serious side effects.
[03:58] So an anesthesiologist has to mix
just the right balance of drugs
[04:02] to create all the features of anesthesia,
[04:04] while carefully monitoring
the patient's vital signs,
[04:08] and adjusting the drug mixture as needed.
[04:10] Anesthesia is complicated,
[04:13] but figuring out how to use it
[04:14] allowed for the development 
of new and better surgical techniques.
[04:18] Surgeons could learn how to routinely
and safely perform C-sections,
[04:23] reopen blocked arteries,
[04:25] replace damaged livers and kidneys,
[04:27] and many other life-saving operations.
[04:30] And each year, new anesthesia techniques
are developed
[04:33] that will ensure more and more patients
survive the trauma of surgery.