general anesthesia

Anesthesia, General

Definition

General anesthesia is the induction of a state of unconsciousness with the absence of pain sensation over the entire body, through the administration of anesthetic drugs. It is used during certain medical and surgical procedures.

Purpose

General anesthesia has many purposes including:

pain relief (analgesia)
blocking memory of the procedure (amnesia)
producing unconsciousness
inhibiting normal body reflexes to make surgery safe and easier to perform
relaxing the muscles of the body

Description

Anesthesia performed with general anesthetics occurs in four stages which may or may not be observable because they can occur very rapidly:

Stage One: Analgesia. The patient experiences analgesia or a loss of pain sensation but remains conscious and can carry on a conversation.
Stage Two: Excitement. The patient may experience delirium or become violent. Blood pressure rises and becomes irregular, and breathing rate increases. This stage is typically bypassed by administering a barbiturate, such as sodium pentothal, before the anesthesia.
Stage Three: Surgical Anesthesia. During this stage, the skeletal muscles relax, and the patient's breathing becomes regular. Eye movements slow, then stop, and surgery can begin.
Stage Four: Medullary Paralysis. This stage occurs if the respiratory centers in the medulla oblongata of the brain that control breathing and other vital functions cease to function. Death can result if the patient cannot be revived quickly. This stage should never be reached. Careful control of the amounts of anesthetics administered prevent this occurrence.

ANESTHETICS: HOW THEY WORK
Type	Name(s)	Administered	Affect
General	Halothane, Enflurane Isoflurane, Ketamine, Nitrous Oxide, Thiopental	Intravenously, Inhalation	Produces total unconsciousness affecting the entire body
Regional	Mepivacaine, Chloroprocaine, Lidocaine	Intravenously	Temporarily inter- rupts transmission of nerve impulses (temperature, touch, pain) and motor functions in a large area to be treated; does not produce unconsciousness
Local	Procaine, Lidocaine, Tetracaine, Bupivacaine	Intravenously	Temporarily blocks transmission of nerve impulses and motor functions in a specific area; does not produce unconsciousness
Topical	Benzocaine, Lidocaine Dibucaine, Pramoxine, Butamben, Tetracaine	Demal (Sprays, Drope, Ointments, Creams, Gels)	Temporarily blocks nerve endings in skin and mucous membranes; does not produce unconsciousness

Agents used for general anesthesia may be either gases or volatile liquids that are vaporized and inhaled with oxygen, or drugs delivered intravenously. A combination of inhaled anesthetic gases and intravenous drugs are usually delivered during general anesthesia; this practice is called balanced anesthesia and is used because it takes advantage of the beneficial effects of each anesthetic agent to reach surgical anesthesia. If necessary, the extent of the anesthesia produced by inhaling a general anesthetic can be rapidly modified by adjusting the concentration of the anesthetic in the oxygen that is breathed by the patient. The degree of anesthesia produced by an intravenously injected anesthesic is fixed and cannot be changed as rapidly. Most commonly, intravenous anesthetic agents are used for induction of anesthesia and then followed by inhaled anesthetic agents.

Key terms

Amnesia — The loss of memory.Analgesia — A state of insensitivity to pain even though the person remains fully conscious.Anesthesiologist — A medical specialist who administers an anesthetic to a patient before he is treated.Anesthetic — A drug that causes unconsciousness or a loss of general sensation.Arrhythmia — Abnormal heart beat.Barbiturate — A drug with hypnotic and sedative effects.Catatonia — Psychomotor disturbance characterized by muscular rigidity, excitement or stupor.Hypnotic agent — A drug capable of inducing a hypnotic state.Hypnotic state — A state of heightened awareness that can be used to modulate the perception of pain.Hypoxia — Reduction of oxygen supply to the tissues.Malignant hyperthermia — A type of reaction (probably with a genetic origin) that can occur during general anesthesia and in which the patient experiences a high fever, muscle rigidity, and irregular heart rate and blood pressure.Medulla oblongata — The lowest section of the brainstem, located next to the spinal cord. The medulla is the site of important cardiac and respiratory regulatory centers.Opioid — Any morphine-like synthetic narcotic that produces the same effects as drugs derived from the opium poppy (opiates), such as pain relief, sedation, constipation and respiratory depression.Pneumothorax — A collapse of the lung.Stenosis — A narrowing or constriction of the diameter of a passage or orifice, such as a blood vessel.General anesthesia works by altering the flow of sodium molecules into nerve cells (neurons) through the cell membrane. Exactly how the anesthetic does this is not understood since the drug apparently does not bind to any receptor on the cell surface and does not seem to affect the release of chemicals that transmit nerve impulses (neurotransmitters) from the nerve cells. It is known, however, that when the sodium molecules do not get into the neurons, nerve impulses are not generated and the brain becomes unconscious, does not store memories, does not register pain impulses from other areas of the body, and does not control involuntary reflexes. Although anesthesia may feel like deep sleep, it is not the same. In sleep, some parts of the brain speed up while others slow down. Under anesthesia, the loss of consciousness is more widespread.When general anesthesia was first introduced in medical practice, ether and chloroform were inhaled with the physician manually covering the patient's mouth. Since then, general anesthesia has become much more sophisticated. During most surgical procedures, anesthetic agents are now delivered and controlled by computerized equipment that includes anesthetic gas monitoring as well as patient monitoring equipment. Anesthesiologists are the physicians that specialize in the delivery of anesthetic agents. Currently used inhaled general anesthetics include halothane, enflurane, isoflurane, desfluorane, sevofluorane, and nitrous oxide.

Halothane (Fluothane) is a powerful anesthetic and can easily be overadministered. This drug causes unconsciousness but little pain relief so it is often used with other agents to control pain. Very rarely, it can be toxic to the liver in adults, causing death. It also has the potential for causing serious cardiac dysrhythmias. Halothane has a pleasant odor, and was frequently the anesthetic of choice for use with children, but since the introduction of sevofluorane in the 1990s, halothane use has declined.
Enflurane (Ethrane) is less potent and results in a more rapid onset of anesthesia and faster awakening than halothane. In addition, it acts as an enhancer of paralyzing agents. Enflurane has been found to increase intracranial pressure and the risk of seizures; therefore, its use is contraindicated in patients with seizure disorders.
Isoflurane (Forane) is not toxic to the liver but can cause some cardiac irregularities. Isofluorane is often used in combination with intravenous anesthetics for anesthesia induction. Awakening from anesthesia is faster than it is with halothane and enfluorane.
Desfluorane (Suprane) may increase the heart rate and should not be used in patients with aortic valve stenosis; however, it does not usually cause heart arrhythmias. Desflurane may cause coughing and excitation during induction and is therefore used with intravenous anesthetics for induction. Desflurane is rapidly eliminated and awakening is therefore faster than with other inhaled agents.
Sevofluorane (Ultane) may also cause increased heart rate and should not be used in patients with narrowed aortic valve (stenosis); however, it does not usually cause heart arrhythmias. Unlike desfluorane, sevofluorane does not cause any coughing or other related side effects, and can therefore be used without intravenous agents for rapid induction. For this reason, sevofluorane is replacing halothane for induction in pediatric patients. Like desfluorane, this agent is rapidly eliminated and allows rapid awakening.
Nitrous oxide (laughing gas) is a weak anesthetic and is used with other agents, such as thiopental, to produce surgical anesthesia. It has the fastest induction and recovery and is the safest because it does not slow breathing or blood flow to the brain. However, it diffuses rapidly into air-containing cavities and can result in a collapsed lung (pneumothorax) or lower the oxygen contents of tissues (hypoxia).

Commonly administered intravenous anesthetic agents include ketamine, thiopental, opioids, and propofol.

Ketamine (Ketalar) affects the senses, and produces a dissociative anesthesia (catatonia, amnesia, analgesia) in which the patient may appear awake and reactive, but cannot respond to sensory stimuli. These properties make it especially useful for use in developing countries and during warfare medical treatment. Ketamine is frequently used in pediatric patients because anesthesia and analgesia can be achieved with an intramuscular injection. It is also used in high-risk geriatric patients and in shock cases, because it also provides cardiac stimulation.
Thiopental (Pentothal) is a barbiturate that induces a rapid hypnotic state of short duration. Because thiopental is slowly metabolized by the liver, toxic accumulation can occur; therefore, it should not be continuously infused. Side effects include nausea and vomiting upon awakening.
Opioids include fentanyl, sufentanil, and alfentanil, and are frequently used prior to anesthesia and surgery as a sedative and analgesic, as well as a continuous infusion for primary anesthesia. Because opioids rarely affect the cardiovascular system, they are particularly useful for cardiac surgery and other highrisk cases. Opioids act directly on spinal cord receptors, and are freqently used in epidurals for spinal anesthesia. Side effects may include nausea and vomiting, itching, and respiratory depression.

Propofol (Diprivan) is a nonbarbiturate hypnotic agent and the most recently developed intravenous anesthetic. Its rapid induction and short duration of action are identical to thiopental, but recovery occurs more quickly and with much less nausea and vomiting. Also, propofol is rapidly metabolized in the liver and excreted in the urine, so it can be used for long durations of anesthesia, unlike thiopental. Hence, propofol is rapidly replacing thiopental as an intravenous induction agent. It is used for general surgery, cardiac surgery, neurosurgery, and pediatric surgery.

General anesthetics are given only by anesthesiologists, the medical professionals trained to use them. These specialists consider many factors, including a patient's age, weight, medication allergies, medical history, and general health, when deciding which anesthetic or combination of anesthetics to use. General anesthetics are usually inhaled through a mask or a breathing tube or injected into a vein, but are also sometimes given rectally.General anesthesia is much safer today than it was in the past. This progress is due to faster-acting anesthetics, improved safety standards in the equipment used to deliver the drugs, and better devices to monitor breathing, heart rate, blood pressure, and brain activity during surgery. Unpleasant side effects are also less common.

Recommended dosage

The dosage depends on the type of anesthetic, the patient's age and physical condition, the type of surgery or medical procedure being done, and other medication the patient takes before, during, or after surgery.

Precautions

Although the risks of serious complications from general anesthesia are very low, they can include heart attack, stroke, brain damage, and death. Anyone scheduled to undergo general anesthesia should thoroughly discuss the benefits and risks with a physician. The risks of complications depend, in part, on a patient's age, sex, weight, allergies, general health, and history of smoking, drinking alcohol, or drug use. Some of these risks can be minimized by ensuring that the physician and anesthesiologist are fully informed of the detailed health condition of the patient, including any drugs that he or she may be using. Older people are especially sensitive to the effects of certain anesthetics and may be more likely to experience side effects from these drugs.Patients who have had general anesthesia should not drink alcoholic beverages or take medication that slow down the central nervous system (such as antihistamines, sedatives, tranquilizers, sleep aids, certain pain relievers, muscle relaxants, and anti-seizure medication) for at least 24 hours, except under a doctor's care.

Special conditions

People with certain medical conditions are at greater risk of developing problems with anesthetics. Before undergoing general anesthesia, anyone with the following conditions should absolutely inform their doctor.ALLERGIES. Anyone who has had allergic or other unusual reactions to barbiturates or general anesthetics in the past should notify the doctor before having general anesthesia. In particular, people who have had malignant hyperthermia or whose family members have had malignant hyperthermia during or after being given an anesthetic should inform the physician. Signs of malignant hyperthermia include rapid, irregular heartbeat, breathing problems, very high fever, and muscle tightness or spasms. These symptoms can occur following the administration of general anesthesia using inhaled agents, especially halothane. In addition, the doctor should also be told about any allergies to foods, dyes, preservatives, or other substances.PREGNANCY. The effects of anesthetics on pregnant women and fetuses vary, depending on the type of drug. In general, giving large amounts of general anesthetics to the mother during labor and delivery may make the baby sluggish after delivery. Pregnant women should discuss the use of anesthetics during labor and delivery with their doctors. Pregnant women who may be given general anesthesia for other medical procedures should ensure that the treating physician is informed about the pregnancy.BREASTFEEDING. Some general anesthetics pass into breast milk, but they have not been reported to cause problems in nursing babies whose mothers were given the drugs.OTHER MEDICAL CONDITIONS. Before being given a general anesthetic, a patient who has any of the following conditions should inform his or her doctor:

neurological conditions, such as epilepsy or stroke
problems with the stomach or esophagus, such as ulcers or heartburn
eating disorders
loose teeth, dentures, bridgework
heart disease or family history of heart problems
lung diseases, such as emphysema or asthma
history of smoking
immune system diseases

arthritis or any other conditions that affect movement
diseases of the endocrine system, such as diabetes or thyroid problems

Side effects

Because general anesthetics affect the central nervous system, patients may feel drowsy, weak, or tired for as long as a few days after having general anesthesia. Fuzzy thinking, blurred vision, and coordination problems are also possible. For these reasons, anyone who has had general anesthesia should not drive, operate machinery, or perform other activities that could endanger themselves or others for at least 24 hours, or longer if necessary.Most side effects usually disappear as the anesthetic wears off. A nurse or doctor should be notified if these or other side effects persist or cause problems, such as:

Headache
vision problems, including blurred or double vision
shivering or trembling
muscle pain
dizziness, lightheadedness, or faintness
drowsiness
mood or mental changes
nausea or vomiting
sore throat
nightmares or unusual dreams

A doctor should be notified as soon as possible if any of the following side effects occur within two weeks of having general anesthesia:

severe headache
pain in the stomach or abdomen
back or leg pain
severe nausea
black or bloody vomit
unusual tiredness or weakness
weakness in the wrist and fingers
weight loss or loss of appetite
increase or decrease in amount of urine
pale skin
yellow eyes or skin

Interactions

General anesthetics may interact with other medicines. When this happens, the effects of one or both of the drugs may be altered or the risk of side effects may be greater. Anyone scheduled to undergo general anesthesia should inform the doctor about all other medication that he or she is taking. This includes prescription drugs, nonprescription medicines, and street drugs. Serious and possibly life-threatening reactions may occur when general anesthetics are given to people who use street drugs, such as cocaine, marijuana, phencyclidine (PCP or angel dust), amphetamines (uppers), barbiturates (downers), heroin, or other narcotics. Anyone who uses these drugs should make sure their doctor or dentist knows what they have taken.

Resources

Books

Dobson, Michael B. Anaesthesia at the District Hospital. 2nd ed. World Health Organization, 2000.

Periodicals

Adachi, Y.U., K. Watanabe, H. Higuchi, and T. Satoh. "The Determinants of Propofol Induction of Anesthesia Dose." Anesthesia and Analgesia 92 (2001): 656-661.

Other

Wenker, O. "Review of Currently Used Inhalation Anesthetics Part I." "The Internet Journal of Anesthesiology." 1999. http://www.ispub.com/journals/IJA/Vol3N2/inhal1.htm.

anesthesia

[an″es-the´ze-ah] 1. lack of feeling or sensation.2. artificially induced loss of ability to feel pain, done to permit the performance of surgery or other painful procedures. It may be produced by a number of agents (anesthetics) capable of bringing about partial or complete loss of sensation.(See accompanying table.)Patient Care. Interventions of the health care team will be individualized based on the type of procedure the patient has undergone and the type of anesthesia administered. Patients recovering from general anesthesia must be assessed constantly until they have reacted. The vital signs and blood pressure are checked regularly; any sudden change is reported immediately. They must be observed to see that the airway is clear at all times. The observation is in specialized recovery rooms called postanesthesia care units that are equipped with a variety of monitors to measure such variables as blood pressure, respiratory and pulse rates, cardiac output, body temperature, fluid balance, and oxygenation. When necessary, patients are initially managed with ventilators that inflate the lungs mechanically through endotracheal tubes. Changes in breathing pattern, eye movements, lacrimation, and muscle tone are indicators for the depth of anesthesia. Breathing patterns are the most sensitive of these.
When patients are awakening from general anesthesia they may be restless, attempting to get out of bed or even striking out at those around them because they are afraid and disoriented. This state is called emergence delirium and should be assessed, as it can indicate hypoxia. Retrograde amnesia may be associated with the administration of anesthesia and adjuncts, causing the patient to forget events occurring in the immediate postoperative period.ambulatory anesthesia anesthesia performed on an outpatient basis for ambulatory surgery.balanced anesthesia anesthesia that uses a combination of drugs, each in an amount sufficient to produce its major or desired effect to the optimum degree and to keep undesirable effects to a minimum.basal anesthesia a reversible state of central nervous system depression produced by preliminary medication so that the inhalation of anesthetic necessary to produce surgical anesthesia is greatly reduced.block anesthesia regional anesthesia.caudal anesthesia a type of regional anesthesia that was used in childbirth between the 1940s and the 1960s. The anesthetizing solution, usually procaine, was injected into the caudal area of the spinal canal through the lower end of the sacrum and affected the caudal nerve roots, rendering the cervix, vagina, and perineum insensitive to pain. Called also caudal block.central anesthesia lack of sensation caused by disease of the nerve centers.closed circuit anesthesia that produced by continuous rebreathing of a small amount of anesthetic gas in a closed system with an apparatus for removing carbon dioxide.compression anesthesia loss of sensation resulting from pressure on a nerve.crossed anesthesia loss of sensation on one side of the face and loss of pain and temperature sense on the opposite side of the body.dissociated anesthesia (dissociation anesthesia) loss of perception of certain stimuli while that of others remains intact.electric anesthesia anesthesia induced by passage of an electric current.endotracheal anesthesia anesthesia produced by introduction of a gaseous mixture through a tube inserted into the trachea.epidural anesthesia regional anesthesia produced by injection of the anesthetic agent into the epidural space. It may be performed by injection of the agent between the vertebral spines in the cervical, thoracic, or lumbar regions. An old method was anesthesia" >caudal anesthesia, which involved injecting the agent into the sacral hiatus. Called also epidural block.general anesthesia a state of unconsciousness produced by anesthestic agents, with absence of pain sensation over the entire body and a greater or lesser degree of muscular relaxation; the drugs producing this state can be administered by inhalation, intravenously, intramuscularly, or rectally, or via the gastrointestinal tract.gustatory anesthesia loss of the sense of taste.hysterical anesthesia loss of tactile sensation occurring as a symptom of conversion disorder, often recognizable by its lack of correspondence with nerve distributions.infiltration anesthesia local anesthesia produced by injection of the anesthetic solution directly into the area of terminal nerve endings. Called also infiltration analgesia.inhalation anesthesia anesthesia produced by the respiration of a volatile liquid or gaseous anesthetic agent.insufflation anesthesia anesthesia produced by introduction of a gaseous mixture into the trachea through a tube.local anesthesia that produced in a limited area, as by injection of a local anesthetic or by freezing with ethyl chloride.open anesthesia general inhalation anesthesia in which there is no rebreathing of the exhaled gases.paraneural anesthesia perineural block.paravertebral anesthesia regional anesthesia produced by the injection of a local anesthetic around the spinal nerves at their exit from the spinal column, and outside the spinal dura. Called also paravertebral block.perineural anesthesia perineural block.peripheral anesthesia lack of sensation due to changes in the peripheral nerves.rectal anesthesia anesthesia produced by introduction of the anesthetic agent into the rectum.refrigeration anesthesia cryoanesthesia.regional anesthesia insensibility caused by interrupting the sensory nerve conductivity of any region of the body; the two primary types are field block, the encircling of an operative field by means of injections of a local anesthetic and nerve block, the making of injections in close proximity to the nerves supplying the area. Called also block.saddle block anesthesia block" >saddle block.segmental anesthesia loss of sensation in a segment of the body due to a lesion of a nerve root.spinal anesthesia anesthesia due to a spinal lesion.regional anesthesia produced by injection of the agent beneath the membrane of the spinal cord. Called also spinal block.surgical anesthesia that degree of anesthesia at which operation may safely be performed.tactile anesthesia loss of the sense of touch" >touch.topical anesthesia that produced by application of a local anesthetic directly to the area involved.

gen·er·al an·es·the·si·a

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

general anesthesia

n. Anesthesia characterized by unconsciousness, muscle relaxation, and loss of sensation over the entire body, and resulting from the administration of a general anesthetic.

general anesthesia

Anesthesiology The administration of pharmacologic agents, via parenteal or inhalation routes, to establish a controlled state of unconsciousness, accompanied by a complete loss of protective reflexes–eg, inability to independently and continuously maintain an airway and regular breathing pattern and respond purposefully to physical stimulation or verbal commands and/or physical stimulation. Cf Conscious sedation, Local anesthesia.

gen·er·al an·es·the·si·a

(jenĕr-ăl anes-thēzē-ă) Loss of ability to perceive pain associated with loss of consciousness produced by intravenous or inhalation anesthetic agents.

gen·er·al an·es·the·si·a

(jenĕr-ăl anes-thēzē-ă) Loss of ability to perceive pain associated with loss of consciousness produced by intravenous or inhalation anesthetic agents.

general anesthesia

general anesthesia

General Anesthesia

general anesthesia

Anesthesia, General

REFERENCES

general anesthesia

Anesthesia, General

Definition

Purpose

Description

Key terms

Recommended dosage

Precautions

Special conditions

Side effects

Interactions

Resources

Books

Periodicals

Other

anesthesia

gen·er·al an·es·the·si·a

general anesthesia

general anesthesia

gen·er·al an·es·the·si·a

gen·er·al an·es·the·si·a

general anesthesia

Synonyms for general anesthesia

noun a state of total unconsciousness resulting from anesthetic drugs (as for a major surgical operation)

Synonyms

Related Words