MADDIE SOFIA: This is Science Friday. I’m Maddie Sofia.

JOHN DANKOSKY: And I’m John Dankosky.

If you’ve ever had surgery, you’ve probably wondered about how anesthesia works. Or maybe even you’ve lied awake at night, anxious about going under. I know I have.

Now, if you’ve ever been there, I’m sure you remember it. It’s right before surgery. You get rolled into the operating room. The anesthesiologist tells you to start counting down from 10. And then the next thing you know, you’re awake in the recovery room. You don’t remember anything that just happened to you.

How exactly did the anesthesiologist manage to get you safely into that state and then back out again?

Joining me now to give us a crash course in anesthesia are my guests. Dr. Louise Sun is a professor of anesthesiology, perioperative, and pain medicine at Stanford University Health, based in Stanford, California. And Dr. Gunisha Kaur is an anesthesiologist and director of the Human Rights Impact Lab and medical director of Weill Cornell Center for Human Rights at Weill Cornell Medicine, based in New York, New York.

Welcome to Science Friday, both of you.

LOUISE SUN: Thank you.

GUNISHA KAUR: Thanks for having us.

JOHN DANKOSKY: And I should let you know that this program was taped on Zoom in advance. And so we’re going to hear a lot of great questions from our audience.

Dr. Kaur, I want to start with you. And, you know, we typically think about it, when we talk about anesthesia, about going to sleep. So first of all, what’s the difference between going to sleep and going under anesthesia?

GUNISHA KAUR: It’s a great question and one that we receive a lot from our patients. There are some critical differences between receiving anesthesia and going to sleep. When you go to sleep, you have the ability to form memories, to wake up, to feel pain. If, for example, while you’re sleeping your dog scratches your leg or your cat scratches your leg or a child wakes you up, you will remember that. You can wake yourself up. You might remember that you feel thirsty or you have to go to the bathroom. And you will wake yourself up and you’ll do those things and you’ll fall back asleep.

Under anesthesia, you don’t form memories in the same way. You don’t remember things in that same way. And you shouldn’t feel pain in that same way. So there are critical differences between sleep and anesthesia.

JOHN DANKOSKY: OK. So why is that? Why don’t I feel pain? Why don’t I remember things? What are you giving me exactly?

GUNISHA KAUR: Well, anesthesia isn’t like a pill that’s given or a machine that’s turned on and off. There are several different anesthetics that are given that are carefully titrated to a person’s individual needs. During a procedure, we monitor and sometimes control a person’s breathing or their heart rate or rhythm, looking at an EKG, their blood pressure. Their blood oxygen and carbon dioxide levels we monitor by pulse oximeter. We look at concentrations of anesthetic gases in the body fluid levels and the body temperature, and sometimes brain activity even.

We give several different medications that affect each of those things. So it’s a combination of medications that really helps provide all of the things that you need to be under anesthesia.

JOHN DANKOSKY: So Dr. Sun, then, what exactly do you do when you’re making this mix? How do you decide how much of this agent and how much of this are we going to use to get this person into exactly the state that we need them to arrive at?

LOUISE SUN: That’s what we term balanced anesthesia. And so what that means is that the cocktail could differ slightly from person to person. And we do want to tailor what we give according to the person’s age, that person’s physiology, pain or stimulation level that we anticipate with the type of surgery that they’re going to undergo. So we tailor all those things to achieve what we call amnesia. So in other words, they don’t have a memory or recall the event; analgesia, which is achieving a painless state, so that they’re comfortable undergoing surgery without overdoing it with the drug dosages, and also that they’re basically immobile for the surgery.

JOHN DANKOSKY: And the doses, as you say, would be different depending on your age. But they could also vary depending on, say, if you take drugs, if you smoke, if you are on some sort of drug regimen for some other health issue, right?

LOUISE SUN: Exactly. Yeah. People, for instance, who drink alcohol or people who are on, say, a cannabis or an opioid medication chronically will have a different tolerance level or threshold for the medications that we give. There are drug-to-drug interactions to consider as well.

There are some interactions that can be deemed to be synergistic, meaning we have to reduce the dosages of certain medications we give, versus there are medications that really don’t interact well and could produce some very dangerous side effects that we have to watch out for. So [INAUDIBLE] pharmacology as well.

JOHN DANKOSKY: I think that we’ve all had the experience of a doctor, during a regular physical exam, asking a question about how much we drink over the week. And we think, should I tell my doctor how much I drink over the week? But this is an example, Dr. Kaur, that really you should. You should tell people, OK, here’s other medications I’m on. Here are some things you need to know about me. Because it’s going to be harder for you to do your job if I don’t.

GUNISHA KAUR: I think there is sometimes a fear of telling your doctor the truth. We all want to present our best selves to our doctors. But I think it’s really critical that your physician knows what medications you’ve been taking. It’s not a problem if, let’s say, you are a smoker, that your surgery is necessarily going to be canceled. That’s not necessarily a problem if you use marijuana recreationally. But those are things that we need to know so that we can provide you the best care.

JOHN DANKOSKY: And then, of course, Dr. Sun, there are different surgeries that are very different. For instance, many people know that during brain surgery there’s a portion of the procedure that you are out for. But there’s another portion of certain procedures where the physician, the surgeon, will want you to be awake during what’s happening.

LOUISE SUN: Those procedures you are referring to in the realm of neurosurgery are called awake craniotomies. Those are surgeries where they’re going around very sensitive motor and speech areas, for instance, where we really want to have a real-time testing of your brain function. So in that case, the anesthesiologist would need to blend their cocktails carefully so that they’re relieving the patient’s anxiety, and the medication will be short-acting enough so that they could be deep asleep when they need to and they can wake up when they need to.

JOHN DANKOSKY: I will say, one of the big fears– and I’m sure that some of our listeners to this program will have some of these same questions– is that people are worried, Dr. Kaur, that they’re going to be knocked out, unable to move, but they’ll still be able to feel what’s going on. First of all, is that possible? Does that ever happen? How often does it happen, if it does?

GUNISHA KAUR: It’s a great question, and I’m so glad you asked it. Because I do get that question a lot from patients, especially if they’ve watched that horror movie, called Awake. Which I have not seen myself, for good reason.

JOHN DANKOSKY: I’m not really interested in watching that, thanks very much.

GUNISHA KAUR: I don’t think you should. This is not a recommendation. This is an anti-recommendation.

[LAUGHTER]

JOHN DANKOSKY: OK.

GUNISHA KAUR: The chances of being awake during anesthesia or having awareness under anesthesia are exceedingly low. There’s a lot of fear because of movies and media. But in reality, awareness under anesthesia occurs in less than 0.1% to 0.2% of cases. So it would probably be more dangerous to walk across the street.

The surgical procedure can be associated with lighter anesthesia depth. So for example, trauma surgeries or emergency surgeries or cardiac surgery with bypass might contribute to that 0.1% to 0.2% number, but it’s still, again, exceedingly rare.

There’s a lot of monitoring that anesthesiologists do in this day and age to ensure that somebody is not awake, not forming memories, and not feeling pain. Which are really critical components of anesthesia for surgical care.

JOHN DANKOSKY: Dr. Sun, I guess I’ll tell a personal story here. I’m one of those anesthesia-phobic people. Because I had a couple rough experiences. I remember one time I came out of surgery– fairly simple surgery for a hernia– I felt drugged for days. It was terrible. I was throwing up forever. And then there was another one where I woke up and I was thrashing side to side. There were orderlies and nurses holding me down. What do you think causes that?

LOUISE SUN: Yeah. And sorry, John, to hear about those experiences. I think it just really speaks to the variability between people, in terms of how their bodies receive the anesthesia medications, and also, really, how anxious you are before you receive general anesthesia. So for instance, what we observe is that patients who are younger, healthier, and extremely anxious before they are put under can wake up quite anxious as well. So I wonder if that partially explains the second circumstance because you had a bad experience the first time around.

And speaking to how the body handles side effects of medications, some people are more prone to be nauseous afterwards and also things like getting confused afterwards and feeling very groggy afterwards. It’s dose dependent, but it’s also person and genetics dependent as well.

JOHN DANKOSKY: This is Science Friday, from WNYC Studios. If you’re just joining us, I’m talking with anesthesiologist Dr. Gunisha Kaur and Dr. Louise Sun, about how anesthesia works.

And now we’re going to take a few of your questions. Suzanne is with us. And Suzanne has a question about people’s age in relation to anesthesia. Suzanne, go ahead.

SUZANNE: Thank you for taking this question. My mother-in-law is about to have surgery. She’s 90 years old and very concerned about going under anesthetic. She’s worried about her brain. She’s worried about waking up. She’s worried about all kinds of things. So the question is, do risks and side effects increase as people age? Thank you.

JOHN DANKOSKY: It’s a great question, Suzanne.

Dr. Kaur, would you like to take that first?

GUNISHA KAUR: Sure. Thank you for the question, and I hope that she does well. We provide anesthesia safely to people of all ages, people who have many comorbidities, who might have heart disease or kidney disease. We can do that safely. And I think talking through those preexisting conditions with your anesthesiologist is going to be a critical component of providing safe anesthesia.

One of the things that we know about anesthesia is that the doses necessary to provide surgical anesthesia change with patient-specific conditions. We know that by each decade of life, anesthetic requirements change. And so that’s something that is well known in anesthesiology, that we can actually shift as we care for her.

JOHN DANKOSKY: Suzanne, thanks so much for that question, and best of luck to you. I really appreciate you asking it.

Terry has a question for us about our brain’s long-term reactions to anesthesia. Go ahead, Terry. You’re on the show.

TERRY: Hi there. Thanks for doing this. I’m just curious, because some of us have had brain injuries and concussions, and then, when we have surgery– I’m actually kind of worried about my brain. I had a shoulder replacement in October. And then, three months later, I had to have knee arthroscopic surgery. So my brain handled the shoulder replacement fairly well. It was kind of mushy and stuff, but it recovered. But boy, after the second one, my brain is just mush. And they have to redo the knee and I’m just terrified. So how does that kind of impact work with the anesthesiology?

JOHN DANKOSKY: That’s a great question, Terry. And I’m glad we’ve got some experts here to help you through that. Dr. Sun, why don’t you try to help Terry through that.

LOUISE SUN: Thanks for the question, Terry. And I really hope your second knee surgery goes well.

Of course, the previous traumatic brain injury is a good consideration for our administration of anesthetic medications and also in terms of the hemodynamic or blood pressure goals that we want to maintain during surgery. One of the things that we really want to be cognizant of is to make sure that the brain gets enough blood supply, and also sometimes in avoidance of being very heavy handed with certain classes of sedation medications that may make people a little more prone to being confused or delirious during the perioperative period.

Of course, all of those have to be balanced out with the need to provide you with the best painkiller regimen that we can for that type of surgery. Because it is a procedure where we don’t want you to be in pain afterwards, which means doctors are probably more likely to employ what they call a multi-modal pain management type of regimen.

JOHN DANKOSKY: Now, we’ve been getting this question from a few folks who submitted before this event. And they’re all asking, why does it seem like no time has passed after waking up from anesthesia, Dr. Kaur?

GUNISHA KAUR: So while we don’t know the exact– like we talked about earlier– molecular mechanism specifically of general anesthetics. We do know in some ways how this anesthesia works and we know a lot about how memory formation is disrupted under general anesthesia. The communication, essentially, between nerves at the synapse is disrupted. So you’re just not forming memories. You’re not processing time. You’re not remembering things in the same way as when you’re awake or when you’re sleeping, like we talked about earlier.

If you’re under general anesthesia, and if it’s sedation, you may be in and out of the anesthesia. So I think both memory formation and the processing of time can be confusing to a person. It might not be what it seems. So if somebody says I was aware under anesthesia, one of the first questions I’d have is, was it general anesthesia or was it sedation? With sedation, particularly light sedation, we would expect that you might be hearing things. You’re not completely asleep. And so time and memory formation are shifted.

JOHN DANKOSKY: Dr. Sun, to close things out– we’ve talked about this a little bit– but there are going to be some people, some of the folks, who ask questions– me, for one– who might be nervous about an upcoming surgery. So what should they make sure to discuss with their anesthesiologist beforehand? What can you tell them to put their mind at ease about the process?

LOUISE SUN: What I often tell our patients is that we’ve done a few of those procedures here before. Which is a bit of a joke. Because we grossly understate the amount of expertise that is required to do the job and to do it well. Some of the things that we discuss, of course, patients are always entitled to ask about the degree of risk they’re taking in pursuing surgery under certain anesthesia techniques. For some procedures, it might be safer to do a sedation rather than a general anesthesia or a nerve block rather than a general anesthesia. There are some cases where general anesthesia might actually be safer than the other modalities of anesthesia.

So I think patients should always be open to talking about the risks and benefits of different anesthesia procedures and also just really come in with an open mind. I let patients have a free shot at asking me anything. And so, over the years, I’ve received many different types of questions and I’ve always been very happy to address them.

JOHN DANKOSKY: Well, I’d like to thank you both very much for addressing all these questions from us. Dr. Louise Sun is a professor of anesthesiology, perioperative, and pain medicine at Stanford University Health, based in Stanford, California. Dr. Gunisha Kaur is an anesthesiologist and director of the Human Rights Impact Lab and medical director of Weill Cornell Center for Human Rights at Weill Cornell Medicine. She’s based in New York, New York.

I’d like to thank you both so much for doing this. Thanks for answering all these questions. I feel like I know a lot more than I did before.

LOUISE SUN: Thanks so much for having us.

GUNISHA KAUR: Thank you.

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