How anesthesia affects your brain and body

Millions of Americans undergo anesthesia each year. Since 1846, doctors have used a variety of drugs to make patients unconscious for surgery, but even though the medications have changed, there's one thing that remains the same- it works. But how exactly? We don't know every detail about what's going on when we administer anesthesia, but then again, we also don't know exactly how consciousness works either. What we do know is that anesthesia interrupts our brain's neural pathways so we don't feel pain. Anesthesiologist Jill Fong explains how it works. Following is a transcript of the video.

Narrator: When you go to sleep, if I pinched you, you'd be up. If I shook you, you'd be up, right? But under anesthesia, I'm gonna pinch you and do a full operation and you're not up. So it's really further on the spectrum of unconsciousness.

Narrator: When you wake up after being put under with general anesthesia you barely feel like any time has passed. You could have been out for an hour or a day and you wouldn't know the difference.

Fong: When you go to a natural sleep, people call your name, your alarm goes off, you wake up, right? This is not what is gonna happen during general anesthesia. You're gonna be unconscious.

Narrator: You're closer to being in a coma than being asleep.

Anesthesia was first used during surgery in 1846. The drug provided at that time was ether. Now anesthesiologists more commonly use a combination of drugs like propofol and fentanyl which interrupt neural pathways so you don't feel pain and you don't remember the surgery.

Fong: Three things that you need for general anesthesia are you need amnesia so that they don't remember, analgesia so they have pain relief and then operating conditions for the surgeon. Some surgeries you need the patient to be very relaxed so you would use a muscle relaxant. Other surgeries the patient just needs to be asleep and anesthetized but they don't need relaxation so how they do that varies upon the different medications that you're using. Some will depress excitatory neurons and some will enhance inhibitory neurons.

Narrator: Excitatory neurons, for example, get excited and send signals to other neurons to fire. Depressing them means less signals telling your brain you're in pain. Inhibitory neurons do the opposite. They make it harder for neurons to generate these electrical signals. In either case this means fewer active neurons overall which is important because when your body is being poked and prodded, neurons would typically fire to tell your brain you're in pain. If those neurons aren't firing, your brain doesn't know that your body is, well, being cut open.

Fong: Basically it interrupts the pathways and the communication between your neural networks. We're aiming for them to be not in pain by looking at their vital signs, their heart rate, their blood pressure. Then we want to make sure that they're unconscious.

Narrator: Without anesthesia, many important surgeries wouldn't be possible because they'd be way too traumatic.

Fong: Surgery didn't move forward, really, until anesthesia moved forward. You know, you watch those old movies. They give you a swig of alcohol, they put a tourniquet and they hack your leg off. People don't do well with that, right? If you had a bad heart, that would be the end of that.

Narrator: After the procedure is complete the doctors stop administering the meds and the most powerful effects of the drugs wear off but even though you're conscious again you might continue to experience some of the drugs side effects.