What is general anesthesia?

Date: Sep-05-2013General anesthesia is the administration of general anesthetic agents that make a person unconscious and unable to feel pain - often used during operative procedures.

The combination of these anesthetic agents - intravenous drugs and inhaled gasses - is intended to induce:

analgesia - loss of response to pain
amnesia - loss of memory
immobility - loss of motor reflexes
unconsciousness
relaxation of skeletal muscles

Local anesthesia, on the other hand, involves numbing a specific part of the body to prevent any feeling of pain during surgical procedures by applying anesthetic drugs.

Anesthesiologists (doctors who specialize in anesthesia) as well as certified registered nurse anesthetists (CRNA) are typically in charge of ensuring that an optimal combination of these agents are given to the patient during surgery.

Attempts to make a general anesthetic were common in ancient Egypt, China and Babylonia.

But it was not until major scientific advancements were made in the late 19th century and the discovery of the germ theory of disease that antiseptic techniques began to develop.

Gradually a better understanding of pharmacology and physiology eventually led to more effective means of controlling of pain and the development of general anesthesia.

According to Medilexicon's medical dictionary1, general anesthesia is:

"loss of ability to perceive pain associated with loss of consciousness produced by intravenous or inhalation anesthetic agents; may include amnesia and muscle relaxation."

The device behind the doctor measures the
awareness of a patient under anesthesia.
How does general anesthesia work?

Even though the biochemical mechanism of action of anesthetics is not very well understood, it is thought that they are able to induce unconsciousness by affecting various sites of the central nervous system (CNS).

However, it is known that general anesthesia affects or interrupts the function of the cerebral cortex, thalamus, reticular activating system, and spinal cord.

The majority of general anesthetics nowadays are administered with a needle, by intravenous injection, or even inhaled in some cases.

Patients who are given general anesthesia have to be very carefully monitored for any changes in blood pressure, pulse, or breathing.

In some cases a tube may be inserted into the patients windpipe to protect the lungs and make breathing easier.

A study carried out by a team from Harvard Medical School, Weill Cornell Medical college and the Massachusetts Institute of Technology found that undergoing general anesthesia is more like a coma than a deep sleep2.
What is general anesthesia used for?

For small areas of the body that need to be numbed, applying local anesthesia is normally sufficient.

Procedures that typically require the administration of general anesthesia include those that:

Cause a lot of blood loss
Take a long time
Affect breathing
Induce anxiety
Are too painful

General anesthesia is considered to be relatively safe because of modern safety standards and equipment. Complications are not that common although they can occur.

GRMC nurse anesthetist Alexzandra Anderson describes the process of placing a patient under anesthesia.
Stages of anesthesia

In 1937 Arthur Ernest Guedel classified the four stages of anesthesia:

Stage 1 "induction" - patients can talk in this stage but they begin to slowly lose consciousness.

Stage 2 "excitement stage" - the patient completely loses consciousness and may experience an irregular heart rate, there may also be uncontrolled movements.

Stage 3 "surgical anesthesia" - the skeletal muscles begin to relax and eye movement stops. The patient is unconscious and ready for surgery at this point.

Stage 4 "overdose" - at this stage too much medication has been administered and the patient experiences severe brain stem or medullary depression - which can be fatal without support.
Risks and complications

For the most part, healthy adults should not have any issues with general anesthesia apart from some mild and temporary symptoms. There is a very small risk of long-term complications occurring and the risk depends on the form of surgery the patient is undergoing. Rarely, general anesthesia can cause lung infections, stroke, heart attack, and even death.

Health conditions or factors that increase the risk of complications, include:

Smoking
Obesity
Diabetes
High blood pressure
Drug allergies
Alcohol abuse
Heart conditions
Sleep apnea - patients with sleep apnea undergoing total joint replacement have 17% fewer complications under regional anesthesia3 compared to general anesthesia, researchers at the Hospital for Special Surgery, New York City, reported in the journal Regional Anesthesia and Pain Medicine.

Researchers at the University of Bordeaux, France, reported that elderly people who undergo general anesthesia have a 35% higher risk of eventually developing dementia4.

The Mayo Clinic reported that children who undergo general anesthesia many times are more likely to develop ADHD5 (attention-deficit hyperactivity disorder).

Anesthesia awareness

Very few people who receive general anesthesia undergo what is known as anesthesia awareness - where they are aware of their surroundings, but do not feel any pain.

Up to 2 in every 1,000 patients under general anesthesia wake up during their operation6, German researchers reported in the journal Deutsches Ärzteblatt International.

In extremely rare cases people can feel pain during surgery, this phenomenon is called unintended intraoperative awareness. The pain is usually unbearable, but because because of muscle relaxants that are given to the patient before surgery, they are not able to tell the surgeon about their distress.

People who experience unintended intraoperative awareness may go on to develop psychological problems, such as post-traumatic stress disorder.

Written by Joseph Nordqvist

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