General anesthesia: uses, risks and side effects


General anesthesia: uses, risks and side effects

General anesthetics bring about a reversible loss of consciousness and analgesia in order for surgeons to operate on a patient. Their usage is commonplace, but how they produce their effect is still not fully understood.

General anesthetics have been widely used in surgery since 1842, when Crawford Long administered diethyl ether to a patient and performed the first painless operation.

In this article, we will cover a number of topics, including the potential side effects of general anesthesia, associated risks and some theories regarding their mode of action.

Here are some key points about general anesthesia. More detail and supporting information is in the main article.

  • General anesthetic was first used in an operation in 1842
  • An anesthesiologist normally administers the general anesthetic prior to an operation
  • There are a large number of known general anesthetic compounds
  • If a procedure is likely to be particularly lengthy, general anesthetic will often be used
  • There are some risks associated with taking general anesthetics, but they are relatively safe when administered correctly
  • Individuals with drug and alcohol addictions have elevated risks of negative health outcomes
  • Very rarely, a patient may experience unintended intraoperative awareness
  • Side effects of general anesthesia can include dizziness and nausea
  • The mechanisms by which anesthesia works are still only partially understood.

What is general anesthesia?

General anesthesia is, essentially, a medically induced coma, not sleep. Drugs render a patient unresponsive and unconscious.

General anesthetics are normally administered intravenously (IV) or inhaled. Under general anesthesia, the patient is unable to feel pain and may also have amnesia.

The drugs will be administered by an anesthesiologist, a specially trained doctor who will also monitor a patient's vital signs and rate of breathing during the procedure.

Stages of general anesthesia

Guedel's classification, designed by Arthur Ernest Guedel in 1937, describes the four stages of anesthesia. Modern anesthetics and updated delivery methods have improved the speed of onset, general safety and recovery, but the four stages remain essentially the same:

General anesthesia is similar to a comatose state and different from sleep.

  • Stage 1 (induction): this phase occurs between the administration of the drug and the loss of consciousness. The patient moves from analgesia without amnesia to analgesia with amnesia
  • Stage 2 (excitement stage): the period following a loss of consciousness, characterized by excited and delirious activity. Breathing and heart rate becomes erratic, and nausea, pupil dilation and breath holding might occur. Because of irregular breathing and a risk of vomiting, there is a real danger of choking; modern, fast-acting drugs aim to limit the time spent in stage 2 of anesthesia
  • Stage 3 (surgical anesthesia): muscles relax, vomiting stops and breathing is depressed. Eye movements slow and then cease. The patient is ready to be operated on
  • Stage 4 (overdose): too much medication has been administered, leading to brain stem or medullary suppression; this results in respiratory and cardiovascular collapse.

The anesthetist's priority is to take the patient to stage 3 of anesthesia as quickly as possible and keep them there for the duration of the surgery.

Reasons for using general anesthetic

There are a number of reasons why general anesthesia may be chosen over local anesthesia (affecting only one part of the body and maintaining consciousness). In some instances, the patient is asked to make a choice between general and local anesthetic.

The main reasons for opting for general anesthetic are:1

  • The procedure is likely to take a long time
  • There is a likelihood of significant blood loss
  • Breathing may be affected - in an operation on the chest, for example
  • The procedure will make the patient feel uncomfortable.

The purpose of general anesthetic is to induce:

  • Analgesia - remove natural response to pain
  • Amnesia - memory loss
  • Immobility - removal of motor reflexes
  • Unconsciousness
  • Skeletal muscle relaxation.

Risks of general anesthesia

Overall, general anesthesia is very safe. Even particularly ill patients can be safely anesthetized; it is the surgical procedure itself which offers the most risk.

Modern general anesthesia is an incredibly safe intervention.

However, older adults and those undergoing lengthy procedures are most at risk of negative outcomes. These outcomes can include postoperative confusion, heart attack, pneumonia and stroke.

Some specific conditions increase the risk to the patient undergoing general anesthetic:

  • Obstructive sleep apnea - a condition where individuals stop breathing while asleep
  • Seizures
  • Existing heart, kidney or lung conditions
  • High blood pressure
  • Alcoholism
  • Smoking
  • History of reactions to anesthesia
  • Medications that can increase bleeding - aspirin, for example
  • Drug allergies
  • Diabetes
  • Obesity or overweight.

Death due to general anesthetic does occur, but only very rarely - roughly 1 in every 100,000-200,000.


On the next page, we look at another risk of general anesthesia, pre-surgical evaluation, side effects and how general anesthetics work.

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Is Surgical Anesthesia Safe? (Video Medical And Professional 2020).

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