Anesthesia is a medical treatment that prevents patients from feeling pain during procedures like surgery, certain screening and diagnostic tests, tissue sample removal (e.g., skin biopsies), and dental work. It allows people to have procedures that lead to healthier and longer lives.

To produce anesthesia, doctors use drugs called anesthetics. Scientists have developed a collection of anesthetic drugs with different effects. These drugs include general, regional, and local anesthetics. General anesthetics make patients unconscious during the procedure while local and regional anesthetics just numb part of the body and allow patients to remain awake.

Depending on the type of pain relief needed, doctors deliver anesthetics by injection, inhalation, topical lotion, spray, eye drops, or skin patch.

General anesthesia affects the whole body, making patients unconscious and unable to move. Surgeons use it when they operate on internal organs and for other invasive or time-consuming procedures such as back surgery. Without general anesthesia, many major, life-saving procedures would not be possible, including open-heart surgery, brain surgery, and organ transplants.

Doctors provide general anesthetics either directly into the bloodstream (intravenously) or as an inhaled gas. General anesthesia delivered intravenously will act quickly and disappear rapidly from the body. This allows patients to go home sooner after surgery. Inhaled anesthetics may take longer to wear off.

General anesthetics typically are very safe. But they can pose risks for some patients, such as the elderly or people with chronic illnesses such as diabetes. Also, side effects may linger for several days in some patients, especially the elderly and children.

Serious side effects—such as dangerously low blood pressure—are much less common than they once were. Still, as with any medical procedure, some risks exist. To minimize these risks, specialized doctors called anesthesiologists carefully monitor unconscious patients and can adjust the amount of anesthetic they receive.

Doctors use local and regional anesthetics to block pain in a part of the body. With these anesthetics, patients stay conscious and comfortable. Usually, patients may go home soon after surgery.

Local anesthetics affect a small part of the body, such as a single tooth. They are often used in dentistry, for eye surgeries such as cataract removal, and to remove small skin growths including warts and moles.

Regional anesthetics affect larger areas, such as an arm, a leg, or everything below the waist. For example, this sort of anesthesia is used for hand and joint surgeries, to ease the pain of childbirth, or during a C-section delivery.

Until recently, we knew very little about how anesthetics work. Scientists are now able to study how the drugs affect specific molecules within cells. Most researchers agree that the drugs target proteins in the membranes around nerve cells. Because inhaled anesthetics have different effects than intravenous ones, scientists suspect that the two types of drugs target different sets of proteins.

Every day, people undergo surgery. Some operations require going deep into the body. Some can take many hours to finish.

Many of these procedures are possible only because of anesthesia. Different types of anesthesia may be used depending on the procedure.

Local anesthesia numbs a small part of the body, such as a tooth. Regional anesthesia is used for larger areas of the body such as an arm, a leg, or everything below the waist. People remain awake during local and regional anesthesia, but pain is reduced or blocked.

General anesthesia uses drugs that make people unconscious and unable to feel pain or move. It’s used for long or invasive procedures. Every year, millions of people in the nation undergo general anesthesia.

“Doctors and nurses have used general anesthesia for over 170 years,” explains Dr. George Mashour, an NIH-funded anesthesia expert at the University of Michigan.

Since that time, new drugs and advances in how patients are monitored have helped make administering anesthesia safer. We know a lot about how general anesthesia affects the heart, lungs, and many other organs. Clinicians can use machines to track how these organs are functioning while people are unconscious. This lets them precisely adjust anesthesia doses to keep people as safe as possible.

But how general anesthesia affects the brain is still not fully understood. NIH-funded researchers are studying ways to track brain activity during anesthesia. This may help them better understand anesthesia’s effects on the brain in general. It may also help them develop safer and more effective drugs.

General anesthesia does come with some risks. A rare complication is awareness under anesthesia. This is when a person gains some awareness during surgery, when they should be unconscious. Most often, this awareness is only of sounds. But sometimes it can include pain.

A more common unwanted effect of surgery and anesthesia is delirium. In delirium, a person is confused and often unclear about what is happening to them. Many people over the age of 60 experience delirium in the days following surgery. It’s also common in children when they awake from anesthesia.

“Ideally, we want to ensure that we are providing enough anesthesia to the brain to suppress consciousness and memory. But we don’t want to provide so much that we induce unwanted effects on brain function after surgery,” says Mashour.

Mashour and his team recently used thin wires placed on the scalp to measure electrical activity in the brain during anesthesia. They saw several shifts in the way areas of the brain communicated while people were unconscious.

Different shifts were seen during different stages of anesthesia, such as going under and waking up. Understanding such brain activity patterns may help scientists develop a brain monitor for anesthesia, Mashour says. Studying anesthesia could also yield insight into consciousness itself and conditions where consciousness is impaired, such as sleep or coma.

If you’re afraid of having general anesthesia, talk with your doctor. They can give you more information about the drugs used. Some procedures can also be done with types of anesthesia where you remain awake.

Ask Your Doctor

Before going under anesthesia, ask:

• Which type of anesthesia will I have? Do I have more than one option?
• Do I need to stop taking any of my medications before anesthesia?
• Do I need to do anything special before I have anesthesia?
• Will I be awake or aware of what is happening during anesthesia?
• Will I feel any pain?
• How soon will I wake up after anesthesia?
• Will I have any side effects from the drugs used?
• How long will I need to stay in the hospital afterward?

Anesthesiologists are doctors who carefully monitor patients throughout surgery and during recovery. They use highly advanced electronic devices that constantly display patients’ blood pressure, blood oxygen levels, heart function, and breathing patterns. These devices have dramatically improved the safety of general anesthesia. They also make it possible to operate on many patients who used to be considered too sick to have surgery.

Anesthesiologists also provide pain relief for less invasive procedures, such as those used to examine blood vessels and internal organs (endoscopy) and during labor and delivery.

As experts in pain management, anesthesiologists may advise patients and their doctors on how to manage pain.

Like all medical doctors, anesthesiologists earn a college degree, often in a life sciences field, then a medical degree (M.D. or D.O.). After that, they complete a 4-year residency program in anesthesiology. Many also train for an additional year or more in a specialty such as pain management, pediatric anesthesiology, or critical care medicine.

When you face surgery, you might have many concerns. One common worry is about going under anesthesia. Will you lose consciousness? How will you feel afterward? Is it safe?

Every day about 60,000 people nationwide have surgery under general anesthesia. It’s a combination of drugs that’s made surgery more bearable for patients and doctors alike. General anesthesia dampens pain, knocks you unconscious and keeps you from moving during the operation.

“Prior to general anesthesia, the best ideas for killing pain during surgery were biting on a stick or taking a swig of whiskey,” says Dr. Emery Brown, an anesthesiologist at Massachusetts General Hospital in Boston. Things improved more than 150 years ago, when a dentist in Massachusetts publicly demonstrated that the anesthetic drug ether could block pain during surgery. Within just a few months, anesthesia was being used in Australia, Europe and then around the world.

“General anesthesia changed medicine practically overnight,” says Brown. Life-saving procedures like open-heart surgery, brain surgery or organ transplantation would be impossible without general anesthesia.

General anesthesia affects your entire body. Other types of anesthesia affect specific regions. Local anesthesia—such as a shot of novocaine from the dentist—numbs only a small part of your body for a short period of time. Regional anesthesia numbs a larger area—such as everything below the waist—for a few hours. Most people are awake during operations with local or regional anesthesia. But general anesthesia is used for major surgery and when it’s important that you be unconscious during a procedure.

General anesthesia has 3 main stages: going under (induction), staying under (maintenance) and recovery (emergence). NIH-funded scientists are working to improve the safety and effectiveness of all 3.

The drugs that help you go under are either breathed in as a gas or delivered directly into your bloodstream. Most of these drugs act quickly and disappear rapidly from your system, so they need to be given throughout the surgery. A specially trained anesthesiologist or nurse anesthetist gives you the proper doses and continuously monitors your vital signs—such as heart rate, body temperature, blood pressure and breathing.

“When patients are going under, they experience a series of deficits,” says Dr. Howard Nash, a scientist at NIH’s National Institute of Mental Health. “The first is an inability to remember things. A patient may be able to repeat words you say, but can’t recall them after waking up.”

Next, patients lose the ability to respond. “They won’t squeeze your fingers or give their name when asked,” Nash says. “Finally they go into deep sedation.”

Although doctors often say that you’ll be asleep during surgery, research has shown that going under anesthesia is nothing like sleep. “Even in the deepest stages of sleep, with prodding and poking we can wake you up,” says Brown. “But that’s not the case with general anesthesia. General anesthesia looks more like a coma—a reversible coma.” You lose awareness and the ability to feel pain, form memories and move.

Once you’ve become unconscious, the anesthesiologist uses monitors and medications to keep you that way. In rare cases, though, something can go wrong. About once in every 1,000 to 2,000 surgeries, patients may gain some awareness when they should be unconscious. They may hear the doctors talking and remember it afterward. Worse yet, they may feel pain but be unable to move or tell the doctors.

“It’s a real problem, although it’s quite rare,” says Dr. Alex Evers, an anesthesiologist at Washington University in St. Louis. “Anesthesia awareness can lead to post-traumatic stress disorder,” a severe anxiety disorder that can arise after a terrifying ordeal.

Scientists have developed strategies to identify and prevent anesthesia awareness. Small studies suggested that brain monitors might help. But in 2008, Evers and his colleagues reported the results of the largest study to compare different techniques. Brain monitoring did no better than standard monitoring in preventing anesthesia awareness.

Addiction to alcohol or drugs increases the risk for anesthesia awareness, but doctors can’t accurately predict who will be affected. A research team in Canada identified variations in a gene A stretch of DNA, a substance you inherit from your parents, that defines characteristics such as eye color, your risk for disease and your likely response to different medications. that may allow animals to form memories while under anesthesia. Ongoing studies are exploring whether this gene plays a role in anesthesia awareness in people.

Other researchers are searching for genes that may affect how anesthetic drugs are processed, or metabolized, by the body. Genetic differences might affect the proper dosage or the selection of drugs for each patient.

Nash and his colleagues have found that studies of the common fruit fly may offer clues to how genes affect anesthesia. When certain repeating segments—called copy number variations—are snipped from the fly’s genome, it affects the insect’s response to anesthesia. Copy number variations are known to affect human responses to other drugs. Nash suspects that these gene segments may also affect how patients react to anesthesia. “As researchers learn more, I expect genetic screening will become more common in the clinic,” says Nash.

After surgery, when anesthesia wears off, you may feel some pain and discomfort. How quickly you recover will depend on the medications you received and other factors like your age. About 40% of elderly patients and up to one-third of children have lingering confusion and thinking problems for several days after surgery and anesthesia.

Right now, the best cure for these side effects is time. Brown and his colleagues are working to develop drugs to help patients more quickly emerge and recover from general anesthesia.

Anesthesia is generally considered quite safe for most patients. “Anesthetics have gotten much safer over the years in terms of the things we’re most worried about, like the patient dying or having dangerously low blood pressure,” Evers says. By some estimates, the death rate from general anesthesia is about 1 in 250,000 patients. Side effects have become less common and are usually not as serious as they once were.

Don’t delay important surgery because of fear of anesthesia. If you have concerns, talk with your doctor. It might help to meet in advance with the person who will give you anesthesia. Ask what kind of anesthesia you will have. Ask about possible risks and side effects. Knowing more might help you feel less concerned about going under.

When You Go Under

General anesthesia has 5 major effects on your body. Researchers are working to develop drugs that target each of these characteristics:

• Lack of Consciousness. Keeps you from being aware of your surroundings.
• Analgesia. Blocks your ability to feel pain.
• Amnesia. Prevents formation of memories.
• Loss of Movement. Relaxes your muscles and keeps you still during surgery.
• Stable Body Functions. Stabilizes your heart rate, blood pressure, temperature, breathing and kidney function.

Scientists are learning more about how anesthetics work at the most basic level. They are also studying the short- and long-term effects of these drugs on specific groups of people, such as the elderly and cancer survivors. These studies will reveal whether certain anesthetics are better than others for members of those groups.

Research on how a person's genetic makeup affects how he or she responds to anesthetics will allow doctors to further tailor drugs for each patient. In the future, scientists hope to design anesthetics that are safer, more effective, and more personalized.

Knowing how anesthetics affect pain and consciousness could also lead to new treatments for conditions that affect consciousness, such as epilepsy or coma. Studies of anesthesia may even help us better understand the nature of consciousness itself.

Anesthesia helps many of us during our lives, whether we need a local painkiller at the dentist, numbing eye drops for laser vision correction or general anesthesia for major surgery. But even though anesthetics have been used in many procedures for more than 150 years, doctors and scientists still don't know exactly how these medicines work in the body.

Finding a Safe Way to Go Under

Before anesthesia, doctors and dentists operated on patients only in extreme circumstances and largely without the use of painkillers or sedatives.

Then, in 1846, dentist William T. G. Morton demonstrated the use of ether to put patients "to sleep" during surgery. The practice soon spread, but because doctors couldn't control the amount of ether inhaled, patients could wake up during surgery—or never wake again. Ether was also highly flammable.

The next few decades saw the introduction of less flammable anesthetic gases as well as the discovery of intravenous anesthetics with controllable dosage. Still, well into the 1950s, dangerous side effects were common and included heart rhythm abnormalities, breathing problems, lowered blood pressure, nausea and vomiting.

Modern anesthetic techniques allow millions of Americans to safely undergo surgery with fewer and less serious side effects. New inhaled and intravenous general anesthetics act quickly and dissipate rapidly when stopped, while local and regional anesthetics that block specific nerves provide an alternative to general anesthesia.

Researchers funded by the National Institutes of Health have helped identify and explore several components of general anesthesia—including sedation, unconsciousness, immobility, analgesia (lack of pain) and amnesia (lack of memory). And they have developed medicines that can provide one or more elements separately, allowing anesthesiologists to tailor painkiller regimens to individual procedures and patients.

An Anesthesiologist's Job Isn't Easy

Since anesthesia can still cause complications and have body-wide effects, anesthesiologists carefully monitor patients throughout surgery using a variety of devices that display blood pressure, blood oxygen levels, heart function and respiration. They adjust medications throughout the procedure to make sure each patient remains safe.

Anesthesiologists' jobs have expanded beyond the operating room as well, including caring for patients as they recover from surgery and providing anesthesia for nonsurgical procedures such as colonoscopy and childbirth. They also advise other specialists on how to manage pain.

"I think it is fair to say that most people have no idea how complex our jobs are and how attentive we must be," says Daniel Kohane, an anesthesiologist at Harvard Medical School and Children's Hospital Boston.

The Future of Anesthesiology

Advances in cell biology, genetics and molecular biology have spurred scientists to learn more about anesthesia and develop better anesthetics.

For instance, Max B. Kelz at the University of Pennsylvania found that the processes of going under and waking up from anesthesia are different. Knowing more about how the brain transitions between conscious and unconscious states could improve our understanding of sleep disorders and states of impaired consciousness such as comas. Daniel Sessler at the University of Louisville School of Medicine found that red-haired women need 20 percent more anesthetic than dark-haired women, and he may have pinpointed a genetic variant that explains why. And Kohane created a slow-release anesthetic that lasted several days in rats and didn't cause nerve damage or other side effects in the animals. This could be a step on the path to improved treatment for chronic pain.

The researchers' ultimate goal is to design anesthetics that are more targeted within the body and personalized to work safely and effectively in each patient. Plus, research into anesthesia could reveal more about pain, memory, conditions such as epilepsy and coma, and the nature of consciousness itself.

What is anesthesia?

Anesthesia is the use of medicines to prevent pain during surgery and other procedures. These medicines are called anesthetics. They may be given by injection, inhalation, topical lotion, spray, eye drops, or skin patch. They cause you to have a loss of feeling or awareness.

What is anesthesia used for?

Anesthesia may be used in minor procedures, such as filling a tooth. It could be used during childbirth or procedures such as colonoscopies. And it is used during minor and major surgeries.

In some cases, a dentist, nurse, or doctor may give you an anesthetic. In other cases, you may need an anesthesiologist. This is a doctor who specializes in giving anesthesia.

What are the types of anesthesia?

There are several different types of anesthesia:

• Local anesthesia numbs a small part of the body. It might be used on a tooth that needs to be pulled or on a small area around a wound that needs stitches. You are awake and alert during local anesthesia.
• Regional anesthesia is used for larger areas of the body such as an arm, a leg, or everything below the waist. You may be awake during the procedure, or you may be given sedation. Regional anesthesia may be used during childbirth, a Cesarean section(C-section), or minor surgeries.
• General anesthesia affects the whole body. It makes you unconscious and unable to move. It is used during major surgeries, such as heart surgery, brain surgery, back surgery, and organ transplants.

What are the risks of anesthesia?

Anesthesia is generally safe. But there can be risks, especially with general anesthesia, including:

• Heart rhythm or breathing problems
• An allergic reaction to the anesthesia
• Delirium after general anesthesia. Delirium makes people confused. They may be unclear about what is happening to them. Some people over the age of 60 have delirium for several days after surgery. It can also happen to children when they first wake up from anesthesia.
• Awareness when someone is under general anesthesia. This usually means that the person hears sounds. But sometimes they can feel pain. This is rare.