Reduciendo al mínimo el uso de anestesia se protege al cerebro
Los estudios que realiza en el MIT podrían ayudar a despertar a personas que se encuentran en coma.
Aunque desde mediados del siglo 19 se viene usando la anestesia general en forma creciente en el mundo, hasta el día de hoy los especialistas que la aplican reconocen que ignoran sus efectos. Sólo ahora se sabe que al estar anestesiada, la persona está en un estado similar al coma o, incluso, al sueño.
“Sabemos que quien recibe anestesia general va a quedar inconsciente, sin dolor ni recuerdos”, explica a “El Mercurio” el doctor Emery Brown, del Massachusetts Institute of Technology (MIT), quien visitó nuestro país y expuso en el 39° Congreso Chileno de Anestesiología.
“Con el mayor conocimiento de cómo funciona el cerebro gracias a la resonancia magnética, estamos elaborando nuevas técnicas de anestesia y buscando reducir las dosis al mínimo para evitar los efectos secundarios”, agrega este investigador.
Cuidar a los niños
Hoy, además, existe la sospecha de que las drogas anestésicas tienen cierta toxicidad en el sistema nervioso de las personas.
“Esto nos preocupa en el contexto de una población mundial que va envejeciendo, y en que la anestesia puede deteriorar las capacidades intelectuales de los mayores”, dice Brown.
Otra inquietud surge de los estudios con animales, que demuestran que los anestésicos favorecen la muerte de neuronas. “En este caso, investigamos para proteger a los niños que por algún problema de salud deben someterse a numerosas cirugías a temprana edad”, detalla.
Una sorpresa que ha aportado este campo de la investigación es la ketamina, una droga que con una dosis mínima produce un alivio inmediato de la depresión severa. Como hoy los antidepresivos demoran uno o dos meses en funcionar a plenitud, este anestésico puede ser una droga de transición para una crisis depresiva.
Por último, Brown considera que los avances en esta disciplina permitirán a futuro despertar a quienes se encuentren en coma, algo que hoy sucede en forma espontánea y excepcional.
You Won’t Feel A Thing: Your Brain On Anesthesia | WBUR & NPR 25 Apr www.wbur.org/…/you-wont-feel-a-thing-your-brain-on-anesthesia – En caché
Emery Brown, Ph.D., M.D. hms.harvard.edu
You Won’t Feel A Thing: Your Brain On Anesthesia
- April 25, 2011, 8:57 AM
If you’ve gone in for surgery, it’s likely that your anesthesiologist has told you to count backward from 100 — and that you’ll wake up after a nice deep sleep.
But that’s not exactly true.
“Sleep is not the state you’re going in, nor would it be the state in which someone could perform an operation on you,” explains Dr. Emery Brown. “What we need to do in order to be able to operate on you — to perform a procedure which is, indeed, very invasive — is to put you in a state which is effectively a coma which we can readily reverse.”
Brown, a professor of anesthesia at Harvard Medical School and a practicing anesthesiologist at Massachusetts General Hospital, recently co-authored a study in The New England Journal of Medicine outlining what scientists know and don’t know about anesthesia. Unlocking its many mysteries, he says, will help scientists better understand consciousness and sleep — and could lead to new treatments for pain, depression and sleep disorders.
Anesthesia And The Brain
One of medicine’s biggest questions is how anesthesia — which knocks patients unconscious, renders them immune to pain and keeps them immobile during procedures — actually works in the brain. Brown’s team has been conducting imaging studies on volunteers under anesthesia to see how different parts of the brains change activity levels as the volunteers lose and then regain consciousness.
“We would like to understand, when the drugs are given, what areas are turned off and turned on in what sequence to get some sense of how the drugs work,” Brown tells Fresh Air‘s Terry Gross. “We know a lot about the properties of the drugs — in terms of how they’re metabolized by the body and certain behavioral effects they might have. We also know a lot about certain receptors they bind to, but these receptors are all over the brain and central nervous system. But the state of anesthesia is this very complex behavioral state. So to decipher it, we are at first order using the imaging where it is happening. Then, from there, we can start asking other questions: Is this the way we want to do it? Are there other ways to achieve the same state which might be better for our patients?”
So far, researchers have learned that different drugs create different patterns in the brain, Brown says. For example, propofol — one of the most widely used anesthetics — is a very potent drug and initially puts the brain into a state of excitation.
“It doesn’t really cause a state of sedation or anesthesia [initially],” Brown says. “Then what we actually see next is the brain start to slow. [So first you see] a period where the brain is active, and then [when you give] a higher dose, the brain starts to slow.”
In contrast, the drug ketamine — which is used in conjunction with anesthesia to make certain drugs work better — puts the brain into a state of excitation even at higher doses.
“The state of unconsciousness you get with ketamine is created by making the brain active,” Brown says. “As you transition through this active state, you very frequently hallucinate. It’s this hallucination or sense of euphoria or dissociative state that people who are using it as a drug of abuse are seeking.”
Depression And The Brain
Recent studies conducted by scientists at the National Institute of Mental Health have indicated that administering extremely low doses of ketamine can help treat patients with chronic depression. Brown says he is excited by these findings.
“If this turns out to be reproducible, it could change tremendously how chronic depression is managed,” Brown says. “For 70 to 80 percent of patients [in the study who received low doses of ketamine], they felt better almost immediately. This is an exciting finding, because right now there is no way to make a chronically depressed patient feel better immediately. So this is an exciting finding, and if it’s shown to hold, I think it may change tremendously the way chronic depression is treated.”
Defining general anesthesia
“It has five components. You’re supposed to be unconscious. You’re not supposed to have pain. You’re not supposed to remember. And we want you to not move while someone is operating on you. And we want you to be stable physiologically — stable heart rate, stable blood pressure, temperature, breathing. The anesthesiologist takes over the physiology of the patient and controls it for the duration of the time that the patient is having surgery. Then by titrating very carefully the way the medications are given, when the surgery is over, we can reverse the coma.”
On waking up during surgery
“Does it happen, despite our best efforts sometimes? Yes, I think that’s the case. What typically happens more predictably is usually in emergency settings — someone who is coming in to have an emergency cesarean section, and there is concern about how to titrate the level of anesthesia so you can take care of mother as well as the baby. Or another case is someone comes in with massive trauma from a car accident, maybe a gunshot wound. And again, you’re trying to balance the side effects of the anesthetic on the heart and lungs against trying to give the person appropriate levels of anesthetic so he or she can tolerate the surgery that’s necessary. There’s one situation historically where there had been a fair amount of recall or awareness under anesthesia, and that was with heart surgery, because up until a few years ago, it was done primarily using large doses of opioids. Even though patients were quite comfortable and there was no evidence of stress overtly, they’d report having recall or having been aware of parts of the surgery.”
On having his patients count down from 100 before surgery
“I’ve been using it to demonstrate to the residents how quickly people lose consciousness under anesthesia and to give them a sense of how profoundly it occurs. So it sounds like something you see in the movies, but I actually do it because it’s fairly impressive. People rarely get beyond 90. … You get a sense of how the drugs are affecting the brain. Some people start counting 100, 99, 98, 97 um, um, 95, 94, 90. So they’ll stop remembering. If you think about it, we think of counting as a very simple process, but it’s actually fairly complex because you have to remember what you just said and then remember what the next number in sequence is.”
Emery Brown: ‘Aspects of anaesthesia are consistent with patients in a coma’
Patients under anaesthetic have more in common with coma victims than somebody sleeping, which has medical implications
Dr Emery Neal Brown, 54, is a professor of anaesthesia at Harvard Medical School. He has published more than 150 scholarly papers and recently, in a paper in the New England Journal of Medicine, he outlined the differences between general anaesthesia, sleep and coma. He continues to practise at Massachusetts General Hospital, and is also a professor of computational neuroscience and health sciences and technology at MIT, where he works on developing statistical methods for neuroscience analysis.
Tell me about your research.
Since 2004 we have been doing experiments on animals and humans to understand how the brain works under anaesthesia. So we record the EEGs [brain waves] of patients who are having general anaesthesia, or volunteer subjects, to see and understand what happens in the brain.
And what have you found out?
The main thing is that general anaesthesia is not just about the brain being turned off. Certain parts of the brain are turned off, but in other parts transmission becomes noisier, and in some parts transmission becomes hypersynchronised. All those things can help you be unconscious.
If the brain is turned off, it is easy to understand why a person is unconscious, and that is typical when someone is in a stroke. But have you ever seen someone having a seizure? They are conscious, they lose consciousness as the seizure starts, they come back. If you look at the brain it is highly active in a very synchronous way, and this hypersynchronous state can make a person lose consciousness. It is like having a loud hum down your phone line – you can’t communicate.
We’ve also found many aspects of an EEG of anaesthesia are really consistent with patients who are in a coma. The key difference is that anaesthesia is reversible.
You say a brain under general anaesthesia more closely resembles a brain in coma than asleep. Is the distinction clear?
Your brain is in a completely different state in sleep compared with being in a coma or general anaesthesia, and the differences are not subtle. It is apples and oranges.
Think about it. If you are deeply asleep, I can eventually shake you awake. In a state of general anaesthesia that won’t happen.
Surgery is invasive and traumatic and you need to be in a state that is like a coma to tolerate it. General anaesthesia goes beyond simply controlling pain. It has four components. You are supposed to be unconscious. You are not supposed to remember – having open heart surgery is not an experience you want to remember. Third you must not feel pain and fourth you should not be about to move about. Plus you need to be physiologically stable: heart rate, lungs, blood flow, and body temperature.
And yet we still talk about putting people to sleep…
If you came in for an operation and I told you I was going to put you into a coma, you would probably get up and run away! The idea of being put to sleep is a euphemism. But I think it is important to be honest. We need to educate the public more. For your surgery you need to be in a state of general anaesthesia, not sleep, for the reasons above – I can put you in, I can bring you out.
Before your research, is it true to say that there was little enquiry into how anaesthesia worked? Practitioners were just satisfied that it did work…
I think that attitude is pervasive in our field. There were people looking at how anaesthetics work, but what is different about our work is that we are explicitly saying you have to use neuroscience to do it. What has led research in the past has been pharmacology and receptors [drug binding sites] – to describe how the drugs work. But if the bulk of the effect of the drugs is in the brain and the nervous system, you have to ask what parts of the brain they are working in. Because you can have the same receptor in one area that causes an excitatory effect that in another causes an inhibitory effect.
So do you see anaesthesiology becoming a branch of neuroscience?
Absolutely. It already is! Probably nobody manipulates the brain more than anaesthesiologists. In the US, between 60,000 and 90,000 patients have general anaesthesia daily. That is a lot of expertise accruing about brain neuroscience.
What is the potential of your research?
The possibilities are limitless. Insomnia is a big problem, for example. A lot of insomnia drugs work like low doses of anaesthetic drugs – they create sedation, not sleep. The goal of treating insomnia is to promote natural sleep, but sleep is a cycle, as your brain moves between REM and non-REM sleep, and it can be very active. How can one drug induce a cycle? That is why people who take a sedative may wake up and still feel groggy. They haven’t been through the natural stages of sleep necessary for the body to recover. If we work from what we now know – that anaesthesia isn’t sleep – then we can help.
Can you explain stories of people being aware under anaesthetic?
These are horrible cases and usually occur in emergency, medically complex situations. But it is avoidable. If certain patterns are visible on the EEG, I can feel 100% sure that you’re not going to be aware.
Can you do the same – in reverse – for someone in a coma and see whether they are aware?
Yes, and this is an active area of research by others. We are realising that our ability to communicate with someone in a “coma” may only be limited by our ability to understand how they can respond. So let’s say someone was a tennis player, and we know that tennis players, when they think about a serve, activate a particular part of their brain. You say to the person, “If you are hearing me, pretend you are doing a tennis serve”, and you see the person activate that area of their brain. They are not locked in. If you know how to communicate with them, they can respond. –