General anaesthesia
Encyclopedia
General anaesthesia is a state of unconsciousness
Unconsciousness
Unconsciousness is the condition of being not conscious—in a mental state that involves complete or near-complete lack of responsiveness to people and other environmental stimuli. Being in a comatose state or coma is a type of unconsciousness. Fainting due to a drop in blood pressure and a...

 and loss of protective reflexes resulting from the administration of one or more general anaesthetic
General anaesthetic
A general anaesthetic is a drug that brings about a reversible loss of consciousness. These drugs are generally administered by an anaesthesia provider to induce or maintain general anaesthesia to facilitate surgery...

 agents. A variety of medications may be administered, with the overall aim of ensuring hypnosis
Sleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...

, amnesia
Amnesia
Amnesia is a condition in which one's memory is lost. The causes of amnesia have traditionally been divided into categories. Memory appears to be stored in several parts of the limbic system of the brain, and any condition that interferes with the function of this system can cause amnesia...

, analgesia
Analgesic
An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....

, relaxation of skeletal muscle
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...

s, and loss of control of reflex
Reflex
A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...

es of the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

. The optimal combination of these agents for any given patient and procedure is typically selected by an anaesthesiologist
Anesthesiologist
An anesthesiologist or anaesthetist is a physician trained in anesthesia and peri-operative medicine....

 or another provider such as an anaesthesiologist assistant or nurse anaesthetist
Nurse anesthetist
A nurse anesthetist is a nurse who specializes in the administration of anesthesia.In the United States, a Certified Registered Nurse Anesthetist is an advanced practice registered nurse who has acquired graduate-level education and board certification in anesthesia...

, in consultation with the patient and the medical or dental practitioner
Practitioner
A practitioner is someone who engages in an occupation, profession, religion, or way of life.Practitioner may refer to:* Medical practitioner* Justice practitioner* Solitary practitioner, in Wicca and Paganism...

 performing the operative procedure.

History

Attempts at producing a state of general anesthesia can be traced throughout recorded history
Recorded history
Recorded history is the period in history of the world after prehistory. It has been written down using language, or recorded using other means of communication. It starts around the 4th millennium BC, with the invention of writing.-Historical accounts:...

 in the writings of the ancient Sumer
Sumer
Sumer was a civilization and historical region in southern Mesopotamia, modern Iraq during the Chalcolithic and Early Bronze Age....

ians, Babylonia
Babylonia
Babylonia was an ancient cultural region in central-southern Mesopotamia , with Babylon as its capital. Babylonia emerged as a major power when Hammurabi Babylonia was an ancient cultural region in central-southern Mesopotamia (present-day Iraq), with Babylon as its capital. Babylonia emerged as...

ns, Assyria
Assyria
Assyria was a Semitic Akkadian kingdom, extant as a nation state from the mid–23rd century BC to 608 BC centred on the Upper Tigris river, in northern Mesopotamia , that came to rule regional empires a number of times through history. It was named for its original capital, the ancient city of Assur...

ns, Egyptians
Ancient Egypt
Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

, Greeks
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

, Romans
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

, Indians
Indus Valley Civilization
The Indus Valley Civilization was a Bronze Age civilization that was located in the northwestern region of the Indian subcontinent, consisting of what is now mainly modern-day Pakistan and northwest India...

, and Chinese. During the Middle Ages
Middle Ages
The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

, which correspond roughly to what is sometimes referred to as the Islamic Golden Age
Islamic Golden Age
During the Islamic Golden Age philosophers, scientists and engineers of the Islamic world contributed enormously to technology and culture, both by preserving earlier traditions and by adding their own inventions and innovations...

, scientists and other scholars made significant advances in science and medicine in the Muslim world
Muslim world
The term Muslim world has several meanings. In a religious sense, it refers to those who adhere to the teachings of Islam, referred to as Muslims. In a cultural sense, it refers to Islamic civilization, inclusive of non-Muslims living in that civilization...

 and Eastern world
Eastern world
__FORCETOC__The term Eastern world refers very broadly to the various cultures or social structures and philosophical systems of Eastern Asia or geographically the Eastern Culture...

, while their European counterparts also made important advances.

The European Renaissance
Renaissance
The Renaissance was a cultural movement that spanned roughly the 14th to the 17th century, beginning in Italy in the Late Middle Ages and later spreading to the rest of Europe. The term is also used more loosely to refer to the historical era, but since the changes of the Renaissance were not...

 saw significant advances in anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...

 and surgical technique
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...

. However, despite all this progress, surgery remained a treatment of last resort. Largely because of the associated pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...

, many patients with surgical disorders chose certain death rather than undergo surgery. Although there has been a great deal of debate as to who deserves the most credit for the discovery of general anesthesia, it is generally agreed that certain scientific discoveries in the late 18th and early 19th centuries were critical to the eventual introduction and development of modern anesthetic techniques.

Two "quantum leaps" occurred in the late 19th century, which together allowed the transition to modern
Modernity
Modernity typically refers to a post-traditional, post-medieval historical period, one marked by the move from feudalism toward capitalism, industrialization, secularization, rationalization, the nation-state and its constituent institutions and forms of surveillance...

 surgery. An appreciation of the germ theory of disease
Germ theory of disease
The germ theory of disease, also called the pathogenic theory of medicine, is a theory that proposes that microorganisms are the cause of many diseases...

 led rapidly to the development and application of antiseptic
Antiseptic
Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...

 techniques in surgery. Antisepsis, which soon gave way to asepsis
Asepsis
Asepsis is the state of being free from disease-causing contaminants or, preventing contact with microorganisms. The term asepsis often refers to those practices used to promote or induce asepsis in an operative field in surgery or medicine to prevent infection...

, reduced the overall morbidity and mortality
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...

 of surgery to a far more acceptable rate than in previous eras. Concurrent with these developments were the significant advances in pharmacology
Pharmacology
Pharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function...

 and physiology
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

 which led to the development of general anesthesia and the control of pain.

In the 20th century, the safety and efficacy of general anesthesia was improved by the routine use of tracheal intubation
Tracheal intubation
Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic or rubber tube into the trachea to maintain an open airway or to serve as a conduit through which to administer certain drugs...

 and other advanced airway management
Airway management
In cardiopulmonary resuscitation, anaesthesia, emergency medicine, intensive care medicine and first aid, airway management is the process of ensuring that:# there is an open pathway between a patient’s lungs and the outside world, and...

 techniques. Significant advances in monitoring
Medical monitor
A medical monitor or physiological monitor or display, is an electronic medical device used in medical monitoring that displays the monitored data, and may or may not have the ability to transmit the data on a monitoring network...

 and new anesthetic agents with improved pharmacokinetic
Pharmacokinetics
Pharmacokinetics, sometimes abbreviated as PK, is a branch of pharmacology dedicated to the determination of the fate of substances administered externally to a living organism...

 and pharmacodynamic
Pharmacodynamics
Pharmacodynamics is the study of the biochemical and physiological effects of drugs on the body or on microorganisms or parasites within or on the body and the mechanisms of drug action and the relationship between drug concentration and effect...

 characteristics also contributed to this trend. Finally, standardized training programs for anesthesiologists and nurse anesthetist
Nurse anesthetist
A nurse anesthetist is a nurse who specializes in the administration of anesthesia.In the United States, a Certified Registered Nurse Anesthetist is an advanced practice registered nurse who has acquired graduate-level education and board certification in anesthesia...

s emerged during this period.

Purpose

General anaesthesia has many purposes including:
  1. Analgesia — loss of response to pain,
  2. Amnesia — loss of memory,
  3. Immobility — loss of motor reflexes,
  4. Hypnosis — loss of consciousness,
  5. Skeletal muscle relaxation.

Biochemical mechanism of action

The biochemical
Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

 mechanism of action of general anaesthetics is not yet well understood. To induce unconsciousness, anaesthetics affect the GABA
Gamma-aminobutyric acid
γ-Aminobutyric acid is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays a role in regulating neuronal excitability throughout the nervous system...

 and NMDA systems. For example, halothane
Halothane
Halothane is an inhalational general anesthetic. Its IUPAC name is 2-bromo-2-chloro-1,1,1-trifluoroethane. It is the only inhalational anesthetic agent containing a bromine atom; there are several other halogenated anesthesia agents which lack the bromine atom and do contain the fluorine and...

 is a GABA agonist
Agonist
An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...

, and ketamine
Ketamine
Ketamine is a drug used in human and veterinary medicine. Its hydrochloride salt is sold as Ketanest, Ketaset, and Ketalar. Pharmacologically, ketamine is classified as an NMDA receptor antagonist...

 is an NMDA receptor antagonist
Receptor antagonist
A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...

.

Preanaesthetic evaluation

Prior to planned operation or procedure, the anaesthetist reviews the medical record and/or interviews the patient to determine the best combination of drugs and dosages and the degree to which monitoring
Medical monitor
A medical monitor or physiological monitor or display, is an electronic medical device used in medical monitoring that displays the monitored data, and may or may not have the ability to transmit the data on a monitoring network...

 will be required to ensure a safe and effective procedure. Key factors of this evaluation are the patient's age, body mass index
Body mass index
The body mass index , or Quetelet index, is a heuristic proxy for human body fat based on an individual's weight and height. BMI does not actually measure the percentage of body fat. It was invented between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing...

, medical and surgical history, current medications, and fasting time. Thorough and accurate answering of the questions is important so that the anaesthetist can select the proper anaesthetic drug
Drug
A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

s and procedures. For example, a patient who consumes significant quantities of alcohol or illicit drugs
Recreational drug use
Recreational drug use is the use of a drug, usually psychoactive, with the intention of creating or enhancing recreational experience. Such use is controversial, however, often being considered to be also drug abuse, and it is often illegal...

 could be undermedicated if s/he fails to disclose this fact. This in turn could then lead to anaesthesia awareness
Anesthesia awareness
Anesthesia awareness, or unintended intra-operative awareness occurs during general anesthesia, on the operating table, when the patient has not been given enough of the general anesthetic or analgesic to render the patient unconscious during general anesthesia...

 or dangerously high blood pressure. Commonly used medications (e.g., sildenafil
Sildenafil
Sildenafil citrate, sold as Viagra, Revatio and under various other trade names, is a drug used to treat erectile dysfunction and pulmonary arterial hypertension . It was originally developed by British scientists and then brought to market by the US-based pharmaceutical company Pfizer...

) can interact with anaesthesia drugs; failure to disclose such usage can also increase the risk to the patient. There are some situations (where patients are on a certain medication and must undergo a given procedure) in which local anaesthesia
Local anesthesia
Local anesthesia is any technique to induce the absence of sensation in part of the body, generally for the aim of inducing local analgesia, that is, local insensitivity to pain, although other local senses may be affected as well. It allows patients to undergo surgical and dental procedures with...

 or regional anaesthesia
Regional anaesthesia
Regional anaesthesia is anaesthesia affecting only a large part of the body, such as a limb or the lower half of the body. Regional anaesthetic techniques can be divided into central and peripheral techniques. The central techniques include so called neuraxial blocks...

 can be given, but instead general anaesthesia is chosen, though this is not extremely common due to the fact that general anaesthesia is by nature more dangerous and the agents used react with many more medications.

An important aspect of the preanaesthetic evaluation is that of the patient's airway, involving inspection of the mouth opening and visualisation of the soft tissues of the pharynx
Human pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

. The condition of teeth and location of dental crowns and caps are checked, neck flexibility and head extension observed. If a tracheal tube
Tracheal tube
A tracheal tube is a catheter that is inserted into the trachea in order for the primary purpose of establishing and maintaining a patent airway and to ensure the adequate exchange of oxygen and carbon dioxide. Many different types of tracheal tubes are available, suited for different specific...

 is indicated and airway management is deemed difficult, then alternative methods of tracheal intubation
Tracheal intubation
Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic or rubber tube into the trachea to maintain an open airway or to serve as a conduit through which to administer certain drugs...

, such as fibreoptic intubation, may be required as part of the anaesthetic management.

Premedication

Anaesthesiologists may prescribe or administer a premedication prior to administration of a general anaesthetic. Anaesthetic premedication consists of a drug or combination of drugs that serve to complement or otherwise improve the quality of the anaesthetic.

One example of this is the preoperative administration of clonidine
Clonidine
Clonidine is a sympatholytic medication used to treat medical conditions, such as high blood pressure, some pain conditions, ADHD and anxiety/panic disorder...

, an alpha-2 adrenergic agonist. Clonidine premedication reduces the need for anaesthetic induction agents, as well as the need for volatile anaesthetic agents during maintenance of general anaesthesia, and the need for postoperative analgesics. Clonidine premedication also reduces postoperative shivering, postoperative nausea and vomiting
Postoperative nausea and vomiting
Postoperative nausea and vomiting is an unpleasant complication affecting about a third of the 10% of the population undergoing general anaesthesia each year. This equates to about two million people in the United Kingdom annually.-Impact:...

 and emergence delirium
Delirium
Delirium or acute confusional state is a common and severe neuropsychiatric syndrome with core features of acute onset and fluctuating course, attentional deficits and generalized severe disorganization of behavior...

. In children, clonidine
Clonidine
Clonidine is a sympatholytic medication used to treat medical conditions, such as high blood pressure, some pain conditions, ADHD and anxiety/panic disorder...

 premedication is at least as effective as benzodiazepine
Benzodiazepine
A benzodiazepine is a psychoactive drug whose core chemical structure is the fusion of a benzene ring and a diazepine ring...

s, in addition to having a more favourable side effect profile. It also reduces the incidence of post-operative delirium associated with sevoflurane
Sevoflurane
Sevoflurane , also called fluoromethyl hexafluoroisopropyl ether, is a sweet-smelling, nonflammable, highly fluorinated methyl isopropyl ether used for induction and maintenance of general anesthesia. Together with desflurane, it is replacing isoflurane and halothane in modern anesthesiology...

 anaesthesia. As a result clonidine has become a popular agent for anaesthetic premedication. Drawbacks of oral clonidine include the fact that it can take up to 45 minutes to take full effect, hypotension
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...

 and bradycardia
Bradycardia
Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...

.

Midazolam
Midazolam
Midazolam is a short-acting drug in the benzodiazepine class developed by Hoffmann-La Roche in the 1970s. The drug is used for treatment of acute seizures, moderate to severe insomnia, and for inducing sedation and amnesia before medical procedures. It possesses profoundly potent anxiolytic,...

, a benzodiazepine characterized by a rapid onset and short duration relative to other benzodiazepines, is effective in reducing preoperative anxiety, including separation anxiety
Separation anxiety disorder
Separation anxiety disorder is a psychological condition in which an individual experiences excessive anxiety regarding separation from home or from people to whom the individual has a strong emotional attachment...

 associated with separation of children from their parents and induction of anaesthesia. Dexmedetomidine
Dexmedetomidine
Dexmedetomidine is a sedative medication used by intensive care units and anesthetists. It is relatively unique in its ability to provide sedation without causing respiratory depression...

 and certain atypical antipsychotic
Atypical antipsychotic
The atypical antipsychotics are a group of antipsychotic tranquilizing drugs used to treat psychiatric conditions. Some atypical antipsychotics are FDA approved for use in the treatment of schizophrenia...

 agents are other drugs that are used in particular in very uncooperative children.

Melatonin
Melatonin
Melatonin , also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes...

 has been found to be effective as an anaesthetic premedication in both adults and children due to its hypnotic
Hypnotic
Hypnotic drugs are a class of psychoactives whose primary function is to induce sleep and to be used in the treatment of insomnia and in surgical anesthesia...

, anxiolytic
Anxiolytic
An anxiolytic is a drug used for the treatment of anxiety, and its related psychological and physical symptoms...

, sedative, antinociceptive
Nociception
Nociception is defined as "the neural processes of encoding and processing noxious stimuli." It is the afferent activity produced in the peripheral and central nervous system by stimuli that have the potential to damage tissue...

, and anticonvulsant
Anticonvulsant
The anticonvulsants are a diverse group of pharmaceuticals used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of bipolar disorder, since many seem to act as mood stabilizers, and in the treatment of neuropathic pain. The goal of an...

 properties. Unlike midazolam, melatonin does not impair psychomotor skills
Psychomotor learning
Psychomotor learning is the relationship between cognitive functions and physical movement. Psychomotor learning is demonstrated by physical skills such as movement, coordination, manipulation, dexterity, grace, strength, speed; actions which...

 or adversely affect the quality of recovery. Recovery is more rapid after melatonin premedication than with midazolam, and there is also a reduced incidence of post-operative agitation
Psychomotor agitation
Psychomotor agitation is a series of unintentional and purposeless motions that stem from mental tension and anxiety of an individual. This includes pacing around a room, wringing one's hands, pulling off clothing and putting it back on and other similar actions...

 and delirium. Melatonin premedication also reduces the required induction dose of propofol
Propofol
Propofol is a short-acting, intravenously administered hypnotic agent. Its uses include the induction and maintenance of general anesthesia, sedation for mechanically ventilated adults, and procedural sedation. Propofol is also commonly used in veterinary medicine...

 and thiopental
Sodium thiopental
Sodium thiopental, better known as Sodium Pentothal , thiopental, thiopentone sodium, or Trapanal , is a rapid-onset short-acting barbiturate general anaesthetic...

.

Another example of anaesthetic premedication is the preoperative administration of beta adrenergic antagonists
Adrenergic beta-antagonist
Adrenergic beta-receptor blockaders are "drugs that bind to but do not activate beta-adrenergic receptors thereby blocking the actions of beta-adrenergic agonists...

 to reduce the incidence of postoperative hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...

, cardiac dysrhythmia
Cardiac dysrhythmia
Cardiac dysrhythmia is any of a large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart. The heart beat may be too fast or too slow, and may be regular or irregular.Some arrhythmias are life-threatening medical emergencies that can result in cardiac...

 or myocardial infarction
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...

. One may choose to administer an antiemetic
Antiemetic
An antiemetic is a drug that is effective against vomiting and nausea. Antiemetics are typically used to treat motion sickness and the side effects of opioid analgesics, general anaesthetics, and chemotherapy directed against cancer....

 agent such as droperidol
Droperidol
Droperidol is an antidopaminergic drug used as an antiemetic and antipsychotic...

 or dexamethasone
Dexamethasone
Dexamethasone is a potent synthetic member of the glucocorticoid class of steroid drugs. It acts as an anti-inflammatory and immunosuppressant...

 to reduce the incidence of postoperative nausea and vomiting, or subcutaneous heparin
Heparin
Heparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...

 or enoxaparin to reduce the incidence of deep vein thrombosis
Deep vein thrombosis
Deep vein thrombosis is the formation of a blood clot in a deep vein. Deep vein thrombosis commonly affects the leg veins or the deep veins of the pelvis. Occasionally the veins of the arm are affected...

. Other commonly used premedication agents include opioid
Opioid
An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...

s such as fentanyl or sufentanil
Sufentanil
Sufentanil is a powerful synthetic opioid analgesic drug, approximately 5 to 10 times more potent than its analog, fentanyl. Sufentanil is marketed for use by specialist centres under different trade names, such as Sufenta and Sufentil...

, gastrokinetic
Prokinetic agent
A gastroprokinetic agent, gastrokinetic, or prokinetic, is a type of drug which enhances gastrointestinal motility by increasing the frequency of contractions in the small intestine or making them stronger, but without disrupting their rhythm...

 agents such as metoclopramide
Metoclopramide
Metoclopramide is an antiemetic and gastroprokinetic agent. It is commonly used to treat nausea and vomiting, to facilitate gastric emptying in people with gastroparesis, and as a treatment for the gastric stasis often associated with migraine headaches.-Medical uses:Metoclopramide is commonly...

, and histamine antagonist
Histamine antagonist
A histamine antagonist, commonly referred to as antihistamine, is a pharmaceutical drug that inhibits action of histamine by blocking it from attaching to histamine receptors.- Clinical effects :...

s such as famotidine
Famotidine
Famotidine is a histamine H2-receptor antagonist that inhibits stomach acid production, and it is commonly used in the treatment of peptic ulcer disease and gastroesophageal reflux disease . It is commonly marketed by Johnson & Johnson/Merck under the trade names Pepcidine and Pepcid and by...

.

Non-pharmacologic preanaesthetic interventions include playing relaxing music, massage
Massage
Massage is the manipulation of superficial and deeper layers of muscle and connective tissue to enhance function, aid in the healing process, and promote relaxation and well-being. The word comes from the French massage "friction of kneading", or from Arabic massa meaning "to touch, feel or handle"...

, and reducing ambient light and noise levels in order to maintain the sleep-wake cycle
Circadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...

. These techniques are particularly useful for paediatric
Pediatrics
Pediatrics or paediatrics is the branch of medicine that deals with the medical care of infants, children, and adolescents. A medical practitioner who specializes in this area is known as a pediatrician or paediatrician...

 and mentally retarded
Intellectual disability
Intellectual disability is a broad concept encompassing various intellectual deficits, including mental retardation , deficits too mild to properly qualify as MR, various specific conditions , and problems acquired later in life through acquired brain injuries or neurodegenerative diseases like...

 patients. Other options for children who refuse or cannot tolerate pharmacologic premedication include interventions by clowns and child life specialist
Child life specialist
Child life specialists are pediatric health care professionals who work with patients, their family and others involved in the child’s care in order to help them manage stress and understand medical and various procedures...

s. Minimizing sensory stimulation or distraction by video games may also help to reduce anxiety prior to or during induction of general anaesthesia.

Stages of anaesthesia

The four stages of anaesthesia were described in 1937. Despite newer anaesthetic agents and delivery techniques, which have led to more rapid onset and recovery from anaesthesia, with greater safety margins, the principles remain.

Stage 1: Stage 1 anaesthesia, also known as the "induction", is the period between the initial administration of the induction agents and loss of consciousness. During this stage, the patient progresses from analgesia without amnesia to analgesia with amnesia. Patients can carry on a conversation at this time.
Stage 2: Stage 2 anaesthesia, also known as the "excitement stage", is the period following loss of consciousness and marked by excited and delirious activity. During this stage, respirations and heart rate may become irregular. In addition, there may be uncontrolled movements, vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...

, breath holding, and pupillary dilation. Since the combination of spastic movements, vomiting, and irregular respirations may lead to airway compromise, rapidly acting drugs are used to minimize time in this stage and reach stage 3 as fast as possible.
Stage 3: Stage 3, "surgical anaesthesia". During this stage, the skeletal muscles relax, and the patient's breathing becomes regular. Eye movements slow, then stop, and surgery can begin. It has been divided into 4 planes:
  1. eyes initially rolling, then becoming fixed
  2. loss of corneal and laryngeal reflexes
  3. pupils dilate and loss of light reflex
  4. intercostal paralysis, shallow abdominal respiration, dilated pupils

Stage 4: Stage 4 anaesthesia, also known as "overdose", is the stage where too much medication has been given relative to the amount of surgical stimulation and the patient has severe brain stem or medullary depression. This results in a cessation of respiration and potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support.

Induction

Induction of general anaesthesia is usually conducted in a medical facility
Medical facility
A medical facility is, in general, any location at which medicine is practiced regularly. Medical facilities range from small clinics and doctor's offices to urgent care centers and large hospitals with elaborate emergency rooms and trauma centers. The number and quality of medical facilities in a...

, most commonly in an operating room. However, general anaesthesia may also be conducted in many other locations, such as an endoscopy
Endoscopy
Endoscopy means looking inside and typically refers to looking inside the body for medical reasons using an endoscope , an instrument used to examine the interior of a hollow organ or cavity of the body. Unlike most other medical imaging devices, endoscopes are inserted directly into the organ...

 suite, radiology
Radiology
Radiology is a medical specialty that employs the use of imaging to both diagnose and treat disease visualized within the human body. Radiologists use an array of imaging technologies to diagnose or treat diseases...

 or cardiology
Cardiology
Cardiology is a medical specialty dealing with disorders of the heart . The field includes diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology...

 department, emergency department
Emergency department
An emergency department , also known as accident & emergency , emergency room , emergency ward , or casualty department is a medical treatment facility specialising in acute care of patients who present without prior appointment, either by their own means or by ambulance...

, ambulance
Ambulance
An ambulance is a vehicle for transportation of sick or injured people to, from or between places of treatment for an illness or injury, and in some instances will also provide out of hospital medical care to the patient...

, or at the site of a disaster
Disaster
A disaster is a natural or man-made hazard that has come to fruition, resulting in an event of substantial extent causing significant physical damage or destruction, loss of life, or drastic change to the environment...

 where extrication of the patient may be impossible or impractical.

Anaesthetic agents may be administered by various routes, including inhalation
Inhalation
Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....

, injection
Injection (medicine)
An injection is an infusion method of putting fluid into the body, usually with a hollow needle and a syringe which is pierced through the skin to a sufficient depth for the material to be forced into the body...

 (intravenous
Intravenous therapy
Intravenous therapy or IV therapy is the infusion of liquid substances directly into a vein. The word intravenous simply means "within a vein". Therapies administered intravenously are often called specialty pharmaceuticals...

, intramuscular
Intramuscular injection
Intramuscular injection is the injection of a substance directly into a muscle. In medicine, it is one of several alternative methods for the administration of medications . It is used for particular forms of medication that are administered in small amounts...

 or subcutaneous
Subcutaneous tissue
The hypodermis, also called the hypoderm, subcutaneous tissue, or superficial fascia is the lowermost layer of the integumentary system in vertebrates. Types of cells that are found in the hypodermis are fibroblasts, adipose cells, and macrophages...

), oral
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....

, and rectal
Rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...

. After administration by one or more of these routes, the agents gain access to the blood. Once in the circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

, they are transported to their biochemical sites of action
Active site
In biology the active site is part of an enzyme where substrates bind and undergo a chemical reaction. The majority of enzymes are proteins but RNA enzymes called ribozymes also exist. The active site of an enzyme is usually found in a cleft or pocket that is lined by amino acid residues that...

 in the central
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 and autonomic
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

 nervous systems, where they exert their pharmacologic
Pharmacology
Pharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function...

 effects.

Most general anaesthetics today are induced either with a needle, by intravenous
Intravenous therapy
Intravenous therapy or IV therapy is the infusion of liquid substances directly into a vein. The word intravenous simply means "within a vein". Therapies administered intravenously are often called specialty pharmaceuticals...

 injection, or by breathing a volatile anaesthetic through an anaesthetic circuit (inhalational induction). Onset of anaesthesia is faster with intravenous injection than with inhalation, taking about 10–20 seconds to induce total unconsciousness. This has the advantage of avoiding the excitatory phase of anaesthesia (see above), and thus reduces complications related to induction of anaesthesia. Commonly used intravenous induction agents include propofol
Propofol
Propofol is a short-acting, intravenously administered hypnotic agent. Its uses include the induction and maintenance of general anesthesia, sedation for mechanically ventilated adults, and procedural sedation. Propofol is also commonly used in veterinary medicine...

, sodium thiopental
Sodium thiopental
Sodium thiopental, better known as Sodium Pentothal , thiopental, thiopentone sodium, or Trapanal , is a rapid-onset short-acting barbiturate general anaesthetic...

, etomidate
Etomidate
Etomidate is a short acting intravenous anaesthetic agent used for the induction of general anaesthesia and for sedation for short procedures such as reduction of dislocated joints, tracheal intubation and cardioversion...

, and ketamine
Ketamine
Ketamine is a drug used in human and veterinary medicine. Its hydrochloride salt is sold as Ketanest, Ketaset, and Ketalar. Pharmacologically, ketamine is classified as an NMDA receptor antagonist...

. An inhalational induction may be chosen by the anaesthesiologist where intravenous access is difficult to obtain, where difficulty maintaining the airway is anticipated, or due to patient preference (e.g., children). Sevoflurane
Sevoflurane
Sevoflurane , also called fluoromethyl hexafluoroisopropyl ether, is a sweet-smelling, nonflammable, highly fluorinated methyl isopropyl ether used for induction and maintenance of general anesthesia. Together with desflurane, it is replacing isoflurane and halothane in modern anesthesiology...

 is currently the most commonly used agent for inhalational induction, because it is less irritating to the tracheobronchial tree
Tracheobronchial tree
The tracheobronchial tree is the structure from the trachea, bronchi, and bronchioles that forms the airways that supply air to the lungs. It is within the neck and the chest. The structure looks like a tree because the trachea splits into the right and left mainstem bronchi, which "branch" into...

 than other volatile anaesthetic agents.

Physiologic monitoring

Monitoring involves the use of several technologies to allow for a controlled induction of, maintenance of and emergence from general anaesthesia.
  1. Continuous Electrocardiography (ECG): The placement of electrodes that monitor heart rate and rhythm. This may also help the anaesthetist to identify early signs of heart ischaemia
    Ischemia
    In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...

    .
  2. Continuous pulse oximetry
    Pulse oximetry
    Pulse oximetry is a non-invasive method allowing the monitoring of the oxygenation of a patient's hemoglobin.A sensor is placed on a thin part of the patient's body, usually a fingertip or earlobe, or in the case of an infant, across a foot....

     (SpO2): The placement of this device (usually on one of the fingers) allows for early detection of a fall in a patient's haemoglobin
    Hemoglobin
    Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

     saturation with oxygen (hypoxaemia
    Hypoxia (medical)
    Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

    ).
  3. Blood Pressure Monitoring (NIBP or IBP): There are two methods of measuring the patient's blood pressure. The first, and most common, is called non-invasive blood pressure (NIBP) monitoring. This involves placing a blood pressure cuff around the patient's arm, forearm or leg. A blood pressure machine takes blood pressure readings at regular, preset intervals throughout the surgery. The second method is called invasive blood pressure (IBP) monitoring. This method is reserved for patients with significant heart or lung disease, the critically ill, major surgery such as cardiac or transplant surgery, or when large blood losses are expected. The invasive blood pressure monitoring technique involves placing a special type of plastic cannula in the patient's artery - usually at the wrist or in the groin.
  4. Agent concentration
    Concentration
    In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...

     measurement - Common anaesthetic machine
    Anaesthetic machine
    The anaesthetic machine is used by anaesthesiologists and nurse anaesthetists to support the administration of anaesthesia...

    s have monitors to measure the per cent of inhalational anaesthetic
    Inhalational anaesthetic
    An inhalational anaesthetic is a chemical compound possessing general anaesthetic properties that can be delivered via inhalation. They are administered by anaesthetists through an anaesthesia mask, laryngeal mask airway or tracheal tube connected to some type of anaesthetic vaporiser and an...

     agent used (e.g. sevoflurane
    Sevoflurane
    Sevoflurane , also called fluoromethyl hexafluoroisopropyl ether, is a sweet-smelling, nonflammable, highly fluorinated methyl isopropyl ether used for induction and maintenance of general anesthesia. Together with desflurane, it is replacing isoflurane and halothane in modern anesthesiology...

    , isoflurane
    Isoflurane
    Isoflurane is a halogenated ether used for inhalational anesthesia. Together with enflurane and halothane, it replaced the flammable ethers used in the pioneer days of surgery. Its name comes from being a structural isomer of enflurane, hence they have the same empirical formula...

    , desflurane
    Desflurane
    Desflurane is a highly fluorinated methyl ethyl ether used for maintenance of general anesthesia. Like halothane, enflurane and isoflurane, it is a racemic mixture of and optical isomers...

    , halothane
    Halothane
    Halothane is an inhalational general anesthetic. Its IUPAC name is 2-bromo-2-chloro-1,1,1-trifluoroethane. It is the only inhalational anesthetic agent containing a bromine atom; there are several other halogenated anesthesia agents which lack the bromine atom and do contain the fluorine and...

     etc.). The monitors also usually measure nitrous oxide and oxygen percentages and could give a MAC level.
  5. Low oxygen
    Oxygen
    Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

     alarm - Almost all circuits have a backup alarm in case the oxygen delivery to the patient becomes compromised. This warns if the fraction of inspired oxygen drops lower than minimum alarm setting and allows the anaesthetist to take immediate remedial action.
  6. Circuit disconnect alarm or low pressure alarm indicates failure of circuit to achieve a given pressure during mechanical ventilation
    Mechanical ventilation
    In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows...

    .
  7. Carbon dioxide
    Carbon dioxide
    Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

     measurement (capnography
    Capnography
    Capnography is the monitoring of the concentration or partial pressure of carbon dioxide in the respiratory gases. Its main development has been as a monitoring tool for use during anaesthesia and intensive care. It is usually presented as a graph of expiratory plotted against time, or, less...

    )- measures the amount of carbon dioxide expired by the patient's lungs in per cent or mmHg, mmHg is usually used to allow the anaesthesia provider to see more subtle changes in CO2. It allows the anaesthetist to assess the adequacy of ventilation
    Ventilation (physiology)
    In respiratory physiology, ventilation is the rate at which gas enters or leaves the lung. It is categorized under the following definitions:-Sample values:...

  8. Temperature measurement to discern hypothermia
    Hypothermia
    Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...

     or fever
    Fever
    Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...

    , and to aid early detection of malignant hyperthermia
    Malignant hyperthermia
    Malignant hyperthermia or malignant hyperpyrexia is a rare life-threatening condition that is usually triggered by exposure to certain drugs used for general anesthesia; specifically, the volatile anesthetic agents and the neuromuscular blocking agent, succinylcholine...

    .
  9. EEG or other system to verify depth of anaesthesia may also be used. This reduces the likelihood that a patient will be mentally awake, although unable to move because of the paralytic agents. It also reduces the likelihood of a patient receiving significantly more amnesic drugs than actually necessary to do the job.

Airway management

With the loss of consciousness caused by general anaesthesia, there is loss of protective airway reflexes (such as coughing), loss of airway patency and sometimes loss of a regular breathing pattern due to the effect of anaesthetics, opioid
Opioid
An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...

s, or muscle relaxant
Muscle relaxant
A muscle relaxant is a drug which affects skeletal muscle function and decreases the muscle tone. It may be used to alleviate symptoms such as muscle spasms, pain, and hyperreflexia. The term "muscle relaxant" is used to refer to two major therapeutic groups: neuromuscular blockers and spasmolytics...

s. To maintain an open airway and regulate breathing within acceptable parameters, some form of "breathing tube
Tracheal tube
A tracheal tube is a catheter that is inserted into the trachea in order for the primary purpose of establishing and maintaining a patent airway and to ensure the adequate exchange of oxygen and carbon dioxide. Many different types of tracheal tubes are available, suited for different specific...

" is inserted in the airway after the patient is unconscious. To enable mechanical ventilation
Mechanical ventilation
In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows...

, an endotracheal tube is often used (intubation
Intubation
Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic or rubber tube into the trachea to maintain an open airway or to serve as a conduit through which to administer certain drugs...

), although there are alternative devices such as face masks or laryngeal mask airway
Laryngeal mask airway
The laryngeal mask airway is a supraglottic airway device invented by Archie Brain, a British anaesthetist.-Description:Laryngeal masks consist of a tube with an inflatable cuff that is inserted into the pharynx. Laryngeal mask airways come in a variety of sizes ranging from large adult to infant...

s.

Neuromuscular blockade

"Paralysis" or temporary muscle relaxation with a neuromuscular blocker is an integral part of modern anaesthesia. The first drug used for this purpose was curare
Curare
Curare is a common name for various arrow poisons originating from South America. The three main types of curare are:* tubocurare...

, introduced in the 1940s, which has now been superseded by drugs with fewer side effects and generally shorter duration of action. Muscle relaxation allows surgery
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...

 within major body cavities
Body cavity
By the broadest definition, a body cavity is any fluid-filled space in a multicellular organism. However, the term usually refers to the space located between an animal’s outer covering and the outer lining of the gut cavity, where internal organs develop...

, e.g. abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 and thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...

 without the need for very deep anaesthesia, and is also used to facilitate endotracheal intubation. Acetylcholine, the natural neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

 substance at the neuromuscular junction
Neuromuscular junction
A neuromuscular junction is the synapse or junction of the axon terminal of a motor neuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscle's surface, ultimately causing the muscle to contract...

, causes muscles to contract when it is released from nerve endings. Muscle relaxants work by preventing acetylcholine from attaching to its receptor. Paralysis of the muscles of respiration
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...

, i.e. the diaphragm and intercostal
Intercostal
Intercostal means "between the ribs". It can refer to:* Intercostal muscle* Highest intercostal vein* Intercostal arteries* Intercostal space...

 muscles of the chest requires that some form of artificial respiration be implemented. As the muscles of the larynx
Larynx
The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...

 are also paralysed, the airway
Airway
The pulmonary airway comprises those parts of the respiratory system through which air flows, conceptually beginning at the nose and mouth, and terminating in the alveoli...

 usually needs to be protected by means of an endotracheal tube. Monitoring of paralysis is most easily provided by means of a peripheral nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...

 stimulator. This device intermittently sends short electrical pulses through the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

 over a peripheral nerve while the contraction of a muscle supplied by that nerve is observed. The effects of muscle relaxants are commonly reversed at the termination of surgery by anticholinesterase drugs. Examples of skeletal muscle relaxants in use today are pancuronium
Pancuronium
Pancuronium is a muscle relaxant with various purposes. It is the second of three drugs administered during most lethal injections in the United States.- Mode of action :...

, rocuronium
Rocuronium
Rocuronium is an aminosteroid non-depolarizing neuromuscular blocker or muscle relaxant used in modern anaesthesia, to facilitate endotracheal intubation and to provide skeletal muscle relaxation during surgery or mechanical ventilation.Introduced in 1994, rocuronium has...

, vecuronium
Vecuronium
Vecuronium is a muscle relaxant in the category of non-depolarizing blocking agents. Vecuronium bromide is indicated as an adjunct to general anesthesia, to facilitate endotracheal intubation and to provide skeletal muscle relaxation during surgery or mechanical ventilation...

, atracurium
Atracurium
Atracurium besylate is a neuromuscular-blocking drug or skeletal muscle relaxant in the category of non-depolarizing neuromuscular-blocking drugs, used adjunctively in anesthesia to facilitate endotracheal intubation and to provide skeletal muscle relaxation during surgery or mechanical...

, mivacurium
Mivacurium
Mivacurium chloride is a short-duration non-depolarizing neuromuscular-blocking drug or skeletal muscle relaxant in the category of non-depolarizing neuromuscular-blocking drugs, used adjunctively in anesthesia to facilitate endotracheal intubation and to provide skeletal muscle relaxation during...

, and succinylcholine.

Maintenance

The duration of action of intravenous induction agents is in general 5 to 10 minutes, after which time spontaneous recovery of consciousness will occur. In order to prolong anaesthesia for the required duration (usually the duration of surgery), anaesthesia must be maintained. Usually this is achieved by allowing the patient to breathe a carefully controlled mixture of oxygen, nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...

, and a volatile anaesthetic agent or by having a carefully controlled infusion of medication, usually propofol
Propofol
Propofol is a short-acting, intravenously administered hypnotic agent. Its uses include the induction and maintenance of general anesthesia, sedation for mechanically ventilated adults, and procedural sedation. Propofol is also commonly used in veterinary medicine...

, through an intravenous catheter
Peripheral venous catheter
In medicine, a peripheral venous catheter is a catheter placed into a peripheral vein in order to administer medication or fluids...

. The inhalation agents are transferred to the patient's brain via the lungs and the bloodstream, and the patient remains unconscious. Inhaled agents are frequently supplemented by intravenous anaesthetics, such as opioids (usually fentanyl or a fentanyl derivative) and sedative-hypnotics (usually propofol or midazolam), though, for a propofol-based anaesthetic, supplementation by inhalation agents is not required. At the end of surgery, the volatile or intravenous anaesthetic is discontinued. Recovery of consciousness occurs when the concentration of anaesthetic in the brain drops below a certain level (usually within 1 to 30 minutes, depending upon the duration of surgery). In the 1990s, a novel method of maintaining anaesthesia was developed in Glasgow, UK. Called TCI (target controlled infusion), this involves using a computer-controlled syringe driver (pump) to infuse propofol throughout the duration of surgery, removing the need for a volatile anaesthetic, and allowing pharmacologic principles to more precisely guide the amount of infusion of the drug. Purported advantages include faster recovery from anaesthesia, reduced incidence of post-operative nausea and vomiting, and absence of a trigger for malignant hyperthermia
Malignant hyperthermia
Malignant hyperthermia or malignant hyperpyrexia is a rare life-threatening condition that is usually triggered by exposure to certain drugs used for general anesthesia; specifically, the volatile anesthetic agents and the neuromuscular blocking agent, succinylcholine...

. At present, TCI is not permitted in the United States. Other medications will occasionally be given to anaesthetized patients to treat side-effects or prevent complications. These medications include antihypertensives to treat high blood pressure, drugs like ephedrine
Ephedrine
Ephedrine is a sympathomimetic amine commonly used as a stimulant, appetite suppressant, concentration aid, decongestant, and to treat hypotension associated with anaesthesia....

 and phenylephrine
Phenylephrine
Phenylephrine is a selective α1-adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil, and to increase blood pressure...

 to treat low blood pressure, drugs like salbutamol
Salbutamol
Salbutamol or albuterol is a short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease. It is marketed as Ventolin among other brand names....

 to treat asthma or laryngospasm
Laryngospasm
In medicine, laryngospasm is an uncontrolled/involuntary muscular contraction of the laryngeal cords. The condition typically lasts less than 60 seconds, and causes a partial blocking of breathing in, while breathing out remains easier. It may be triggered when the vocal cords or the area of the...

/bronchospasm
Bronchospasm
Bronchospasm or a bronchial spasm is a sudden constriction of the muscles in the walls of the bronchioles. It is caused by the release of substances from mast cells or basophils under the influence of anaphylatoxins...

, and drugs like epinephrine
Epinephrine
Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...

 or diphenhydramine
Diphenhydramine
Diphenhydramine hydrochloride is a first-generation antihistamine possessing anticholinergic, antitussive, antiemetic, and sedative properties which is mainly used to treat allergies. Like most other first-generation antihistamines, the drug also has a powerful hypnotic effect, and for this reason...

 to treat allergic reactions. Sometimes glucocorticoids or antibiotics are given to prevent inflammation and infection, respectively.

Emergence

Emergence is the process of return to baseline physiologic function of all organ systems after the cessation of administration of general anaesthetic agent(s). This stage of general anaesthesia may be accompanied by certain unusual but temporary neurologic phenomena, such as delirium
Delirium
Delirium or acute confusional state is a common and severe neuropsychiatric syndrome with core features of acute onset and fluctuating course, attentional deficits and generalized severe disorganization of behavior...

 (acute mental confusion), aphasia
Aphasia
Aphasia is an impairment of language ability. This class of language disorder ranges from having difficulty remembering words to being completely unable to speak, read, or write....

 (impaired production or comprehension of speech), or focal impairment in sensory or motor function. Shivering
Shivering
Shivering is a bodily function in response to early hypothermia in warm-blooded animals. When the core body temperature drops, the shivering reflex is triggered to maintain homeostasis. Muscle groups around the vital organs begin to shake in small movements in an attempt to create warmth by...

 is also fairly common and can be clinically significant since it results in an increase in oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 consumption, carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 production, cardiac output
Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...

, heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....

, and systemic blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

. The proposed mechanism is based on the observation that the spinal cord recovers at a faster rate than the brain. This results in uninhibited spinal reflexes manifested as clonic activity (shivering). This theory is supported by the fact that doxapram
Doxapram
Doxapram hydrochloride is a respiratory stimulant. Administered intravenously, doxapram stimulates an increase in tidal volume, and respiratory rate.-Mode of action:...

, a CNS
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 stimulant, is somewhat effective in abolishing postoperative shivering. Cardiovascular events such as increased
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...

 or decreased
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...

 blood pressure, rapid heart rate
Tachycardia
Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...

 or other cardiac dysrhythmia
Cardiac dysrhythmia
Cardiac dysrhythmia is any of a large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart. The heart beat may be too fast or too slow, and may be regular or irregular.Some arrhythmias are life-threatening medical emergencies that can result in cardiac...

s are also common during emergence from general anaesthesia, as are respiratory symptoms such as dyspnoea
Dyspnea
Dyspnea , shortness of breath , or air hunger, is the subjective symptom of breathlessness.It is a normal symptom of heavy exertion but becomes pathological if it occurs in unexpected situations...

.

Postoperative care

The anaesthesia should conclude with a pain-free awakening and a management plan for postoperative pain relief. This may be in the form of regional analgesia
Regional analgesia
Regional analgesia blocks passage of pain impulses through a nerve by depositing an analgesic drug close to the nerve trunk, cutting off sensory innervation to the region it supplies. The drug is normally injected at a site where the nerve is unprotected by bone.-See also:*Local...

, oral, transdermal
Transdermal
Transdermal is a route of administration wherein active ingredients are delivered across the skin for systemic distribution. Examples include transdermal patches used for medicine delivery, and transdermal implants used for medical or aesthetic purposes....

, or parenteral
Parenteral
Parenteral is a route of administration that involves piercing the skin or mucous membrane. Parenteral nutrition refers to providing nutrition via the veins.-Etymology:...

 medication. Minor surgical procedures are amenable to oral pain relief medications such as paracetamol
Paracetamol
Paracetamol INN , or acetaminophen USAN , is a widely used over-the-counter analgesic and antipyretic . It is commonly used for the relief of headaches and other minor aches and pains and is a major ingredient in numerous cold and flu remedies...

 and NSAIDs such as ibuprofen
Ibuprofen
Ibuprofen is a nonsteroidal anti-inflammatory drug used for relief of symptoms of arthritis, fever, as an analgesic , especially where there is an inflammatory component, and dysmenorrhea....

. Moderate levels of pain require the addition of mild opiates such as tramadol
Tramadol
Tramadol hydrochloride is a centrally acting synthetic opioid analgesic used in treating moderate pain. The drug has a wide range of applications, including treatment for restless legs syndrome and fibromyalgia...

. Major surgical procedures may require a combination of modalities to confer adequate pain relief. Parenteral methods include patient-controlled analgesia (PCA) involving a strong opiate such as morphine, fentanyl, or oxycodone. Here, to activate a syringe device, the patient presses a button and receives a preset dose or "bolus" of the drug (e.g., one milligram of morphine). The PCA device then "locks out" for a preset period, e.g. 5 minutes, to allow the drug to take effect. If the patient becomes too sleepy or sedated, he or she make no more morphine requests. This confers a fail-safe aspect that is lacking in continuous-opiate infusion techniques. Shivering is a frequent occurrence in the post-operative period. Apart from causing discomfort and exacerbating post-operative pain, shivering has been shown to increase oxygen consumption, catecholamine release, cardiac output, heart rate, blood pressure, and intra-ocular pressure. There is a number of techniques used to reduce this occurrence, such as increasing the ambient temperature in theatre, using conventional or forced warm air blankets, and using warmed intravenous fluids.

In many cases, opioids used in general anaesthesia can cause post-operative ileus
Ileus
Ileus is a disruption of the normal propulsive ability of the gastrointestinal tract.Ileus is commonly defined simply as bowel obstruction. However, authoritative sources define it as decreased motor activity of the GI tract due to non-mechanical causes...

 even in non-abdominal surgery. Administration of a μ-opioid antagonist
Antagonist
An antagonist is a character, group of characters, or institution, that represents the opposition against which the protagonist must contend...

 such as alvimopan
Alvimopan
Alvimopan is a drug which behaves as a peripherally acting μ-opioid antagonist. With limited ability to cross the blood-brain barrier, many of the undesirable side-effects of the opioid agonists such as constipation are minimized without affecting analgesia or precipitating withdrawals...

 immediately after recovery can help reduce the severity and duration of ileus.

Perioperative mortality

Most perioperative mortality
Perioperative mortality
Perioperative mortality is mortality in relation to surgery, often defined as death within two weeks of a surgical procedure. An important consideration in the decision to perform any surgical procedure is to weigh the benefits against the risks...

 is attributable to complications
Complication (medicine)
Complication, in medicine, is an unfavorable evolution of a disease, a health condition or a medical treatment. The disease can become worse in its severity or show a higher number of signs, symptoms or new pathological changes, become widespread throughout the body or affect other organ systems. A...

 from the operation (such as haemorrhage
Bleeding
Bleeding, technically known as hemorrhaging or haemorrhaging is the loss of blood or blood escape from the circulatory system...

, sepsis
Sepsis
Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...

, and failure of vital organs. This also may include memory loss or slowing down of the thought processes) or pre-existing medical conditions
Comorbidity
In medicine, comorbidity is either the presence of one or more disorders in addition to a primary disease or disorder, or the effect of such additional disorders or diseases.- In medicine :...

. Most current estimates of perioperative mortality range from 1 death in 53 anaesthetics to 1 in 5,417 anaesthetics. However, a 1997 Canadian retrospective review
Retrospective cohort study
A retrospective cohort study, also called a historic cohort study, generally means to take a look back at events that already have taken place...

 of 2,830,000 oral surgical
Oral Surgery
Oral Surgery is a recognized international specialty in dentistry. It includes the diagnosis, surgical and related treatment of diseases, injuries and defects involving both the functional and esthetic aspects of the hard and soft tissues of the head, mouth, teeth, gums, jaws and neck.It involves,...

 procedures in Ontario between 1973–1995 reported only four deaths in cases in which either an oral and maxillofacial surgeon
Oral and maxillofacial surgery
Oral and maxillofacial surgery is surgery to correct a wide spectrum of diseases, injuries and defects in the head, neck, face, jaws and the hard and soft tissues of the oral and maxillofacial region. It is an internationally recognized surgical specialty...

 or a dentist
Dentistry
Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...

 with specialized training in anaesthesia administered the general anaesthetic or deep sedation. The authors calculated an overall mortality rate of 1.4 per 1,000,000. The largest and most recent study of postoperative mortality was published in 2010. In this review of 3.7 million elective
Choice
Choice consists of the mental process of judging the merits of multiple options and selecting one of them. While a choice can be made between imagined options , often a choice is made between real options, and followed by the corresponding action...

 open surgical procedures performed on inpatients at 102 hospitals in the Netherlands during 1991–2005, postoperative mortality from all causes was observed in 67,879 patients, for an overall rate of 1.85%. The wide disparity between the results of these studies may be the result of differences in operational definitions and reporting sources.

Mortality directly related to anaesthetic management is significantly less common, and may include such causes as pulmonary aspiration
Pulmonary aspiration
Pulmonary aspiration is the entry of material from the oropharynx or gastrointestinal tract into the larynx and lower respiratory tract...

 of gastric contents, asphyxia
Asphyxia
Asphyxia or asphyxiation is a condition of severely deficient supply of oxygen to the body that arises from being unable to breathe normally. An example of asphyxia is choking. Asphyxia causes generalized hypoxia, which primarily affects the tissues and organs...

tion and anaphylaxis
Anaphylaxis
Anaphylaxis is defined as "a serious allergic reaction that is rapid in onset and may cause death". It typically results in a number of symptoms including throat swelling, an itchy rash, and low blood pressure...

. These in turn may result from malfunction of anaesthesia-related equipment or more commonly, human error
Human reliability
Human reliability is related to the field of human factors engineering and ergonomics, and refers to the reliability of humans in fields such as manufacturing, transportation, the military, or medicine...

. A 1978 study found that 82% of preventable anaesthesia mishaps were the result of human error. In a 1954 review of 599,548 surgical procedures at 10 hospitals in the United States between 1948–1952, 384 deaths were attributed to anaesthesia, for an overall mortality rate
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...

 of 0.064%. In 1984, after a television programme highlighting anaesthesia mishaps aired in the United States, American anaesthesiologist Ellison C. Pierce appointed a committee called the Anesthesia Patient Safety and Risk Management Committee of the American Society of Anesthesiologists
American Society of Anesthesiologists
The American Society of Anesthesiologists is an association of physicians, primarily anesthesiologists, that share a common goal of raising the standard of the medical specialty of anesthesiology and the improvement of patient care by fostering and encouraging education through research and...

. This committee was tasked with determining and reducing the causes of peri-anaesthetic morbidity and mortality. An outgrowth of this committee, the Anesthesia Patient Safety Foundation was created in 1985 as an independent, nonprofit corporation with the vision that "that no patient shall be harmed by anesthesia". As with perioperative mortality rates in general, the current mortality attributable to the management of general anaesthesia is controversial. The incidence of perioperative mortality that is directly attributable to anaesthesia ranges from 1 in 6,795 to 1 in 200,200 anaesthetics.

External links

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