General anaesthesia and airway management

• General anaesthesia is a drug-induced state of unconsciousness, analgesia, muscle relaxation and loss of protective reflexes that allows surgery without pain, movement or awareness.
• A safe general anaesthetic combines several drugs with different jobs: an induction agent, an opioid, a neuromuscular blocker and an inhalational agent used in measured doses.
• The airway must be assessed before every anaesthetic, and the team must have a plan for the expected difficulty and for the unexpected difficulty.
• If intubation fails, oxygenation stays the priority: three attempts, then a supraglottic airway, then waking the patient, and in a cannot-intubate-cannot-oxygenate emergency, scalpel cricothyroidotomy.
• Malignant hyperthermia and severe postoperative nausea are both treatable emergencies: give dantrolene early for one, and reduce the anaesthetic triggers and give antiemetics for the other.

By the end of this page you should be able to:

1. Name the stages of general anaesthesia and the role of each drug group.
2. Induce anaesthesia with propofol and a neuromuscular blocker, and state the doses, routes and precautions of the common agents.
3. Carry out a preoperative airway assessment and explain which features predict difficult mask ventilation or laryngoscopy.
4. Perform or assist at a rapid sequence induction, including cricoid pressure and preoxygenation.
5. Describe the Difficult Airway Society 2015 plan for unanticipated difficult intubation and the American Society of Anesthesiologists 2022 guidance on difficult airway management.
6. Recognise and treat malignant hyperthermia and postoperative nausea and vomiting.

This page is a procedure reference for the whole of general anaesthesia and airway management rather than a single operation. It sets out how a modern anaesthetic is assembled, how the patient is assessed, how the airway is secured, how the patient is monitored, and how the common emergencies are managed. It is written for a medical student meeting the topic for the first time. ^[3] Doses are typical adult doses; check your local formulary and the patient before giving any drug. Low-resource notes are given because many readers will work in places without videolaryngoscopy, capnography or dantrolene.

The editions named below are the ones used for the statements in this page: the Difficult Airway Society 2015 guidelines for unanticipated difficult intubation in adults (DAS 2015), the 2022 American Society of Anesthesiologists Practice Guidelines for Management of the Difficult Airway (ASA 2022), and the StatPearls chapters on general anaesthesia, malignant hyperthermia, postoperative nausea and airway assessment. Single-drug doses come from the manufacturer product labels.

General anaesthesia is used when a patient needs to be completely unaware and unresponsive during an operation or procedure, and when regional or local techniques alone are not suitable. Common indications include major body cavity surgery, operations where the airway is shared with the surgeon (head and neck, thoracic, upper gastro-intestinal), situations in which patient cooperation cannot be obtained, and patients whose medical condition makes neuraxial or regional blockade unsafe. It is also used for some imaging and for cardioversion in children.

There are few absolute contraindications to general anaesthesia itself, because the decision is one of overall risk, not of one drug. Common relative contraindications and cautions include a known or suspected personal or family history of malignant hyperthermia, uncontrolled cardiorespiratory disease, a difficult airway that has not been planned for, severe hypovolaemia, and patient refusal. Known hypersensitivity to a specific agent rules out that agent, not all anaesthesia.

The airway has to be understood in terms of what can block it and what can be reached. From the lips to the cricoid cartilage, the larynx sits in front of the oesophagus with the epiglottis as a shared flap. The vocal cords are the narrowest visible adult airway. The cricoid cartilage is the only complete ring below the vocal cords and is the landmark for cricoid pressure and for emergency cricothyroidotomy. The mandible, maxilla, hyoid, tongue and soft palate determine how easily the jaw can be lifted and how much space there is in the oropharynx. The neck length, cervical spine mobility and any swelling or lesion (mass, infection, angioedema, haematoma) determine both intubation difficulty and the possibility of a surgical airway. ^[1]

• Operating room with oxygen, suction, working ventilator and vaporiser.
• Monitoring: three-lead or five-lead ECG, pulse oximetry, non-invasive blood pressure, end-tidal carbon dioxide capnography, temperature, and neuromuscular monitoring (peripheral nerve stimulator). Cerebral monitors such as the bispectral index are optional.
• Airway: bag-valve-mask with face masks in several sizes, oropharyngeal and nasopharyngeal airways, laryngoscopes (direct and videolaryngoscope), tracheal tubes in a range of sizes, a gum-elastic bougie, a stylet, forceps and a laryngeal mask or other supraglottic airway device (second-generation if available).
• Drugs: induction agent, opioid, neuromuscular blocker, volatile agent, vasoactive drugs, dantrolene for malignant hyperthermia where the trigger is used.
• Rescue: a prepared difficult airway trolley or bag with the equipment for the DAS 2015 plan, including cricothyroidotomy equipment.
• A stylet or bougie, suction, and capnography must be working before induction. A continuous capnography waveform with appropriate inspired and end-tidal values of carbon dioxide is the gold standard for confirming that the tube is in the trachea.^[1]

Explain the anaesthetic in terms the patient can understand, take consent, confirm fasting (standard local fasting times, usually a longer fast for solid food than for clear fluids), assess aspiration risk and note the indications for rapid sequence induction. Insert a large-bore intravenous cannula, give premedication if used, and re-check the patient on the operating table. Preoperative airway assessment should be performed routinely, and the staff should discuss the strategy before induction in the team brief and at sign-in. Assess the risk of aspiration: fasting, gastric drainage by nasogastric tube where appropriate, and a decision about cricoid pressure.^[1]

Airway assessment is imperfect: no bedside test predicts every difficult airway, and every anaesthetist should approach every patient as if a difficult airway is possible.^[1] Useful elements are history (previous difficult intubation, obstructive sleep apnoea, stridor, hoarseness, rheumatoid arthritis, obesity, pregnancy), examination (mouth opening, neck mobility, mandibular prominence, teeth, interdental distance, thyromental distance, neck circumference and any swelling, tumour or infection) and, where indicated, imaging.

The Mallampati score (also called the modified Mallampati classification) grades how much of the posterior pharynx can be seen when the patient opens the mouth and protrudes the tongue: Class I shows the full tonsillar pillars, Class II shows the soft palate and part of the uvula, Class III shows only the soft palate, and Class IV shows only the hard palate. Higher classes are associated with more difficult intubation, but the score is a predictor, not a diagnosis. A difficult airway also means different things in different patients: difficult mask ventilation, difficult supraglottic airway placement and difficult front-of-neck access each need their own assessment.^[6]

Classically, general anaesthesia passes through four stages: analgesia, with consciousness present but sensation blunted; excitement, with irregular breathing and possible movement as consciousness is lost; surgical anaesthesia, the safe plateau in which the patient is unconscious, does not move and has adequate reflex depression; and overdose, recognised by increasing cardiorespiratory depression and requiring reversal or reduction of doses. In modern practice the stages are compressed by combinations of drugs and by continuous monitoring, but the concepts remain clinically relevant, especially during induction and emergence.

A modern general anaesthetic is "balanced": several drug groups are combined so that each is used in a smaller dose than would be needed on its own. These components are unconsciousness or hypnosis (an induction agent and then usually a volatile or infusion), analgesia (an opioid or regional block), muscle relaxation where needed (a neuromuscular blocker), and abolition or suppression of the autonomic response to surgery (depth of anaesthesia, opioid and sometimes vasodilator or vasopressor). Antiemetics, anxiolytics and antibiotics are added as routine components rather than as anaesthetic agents.

The common routes into general anaesthesia are an intravenous induction or an inhalational induction. In adults an intravenous induction is almost always used; inhalational induction is more common in children without intravenous access and in some adults who refuse or cannot receive an intravenous cannula.

Propofol is the most widely used induction agent. It suppresses laryngeal reflexes and gives better conditions for airway management than other agents.^[1] Typical doses from the product label are shown in the table. ^[7]

Alternatives include thiopental, ketamine and etomidate. Ketamine preserves airway reflexes and haemodynamics and is useful in hypovolaemia, shock and in children; etomidate is chosen when haemodynamic stability is the priority; thiopental is largely replaced by propofol. Nitrous oxide and the volatile agents can be used for inhalational induction, particularly in children, at concentrations titrated to effect. Where ketamine is used, be aware of the risk of emergence delirium and raised intracranial pressure. None of these alternatives replaces propofol as the default in healthy adults in most units; the choice is determined by the patient, not by habit.

The volatile agents in modern practice are sevoflurane, desflurane and isoflurane; nitrous oxide is a gas with lower potency that is added to reduce the dose of the volatile agent. Halothane is now largely abandoned because it triggers malignant hyperthermia and hepatitis, but it remains a known trigger and historical comparator. Potency is expressed as minimum alveolar concentration (MAC), the end-tidal concentration that prevents movement in response to a surgical stimulus in half of patients. Sevoflurane has a MAC of 2.1% in oxygen for a 40-year-old adult, and this falls with age; its blood-gas partition coefficient of 0.63 to 0.69 explains the rapid induction and emergence. ^[10] Nitrous oxide and isoflurane or desflurane speeds induction and recovery because of low solubility. The choice between volatiles is made on speed of emergence, airway irritancy (desflurane is more pungent), organ function and cost. Maintenance concentrations and carrier gas mixtures are adjusted to the patient and the surgery and are guided by depth of anaesthesia monitoring where available. ^[7]

Neuromuscular blockers may be depolarising or non-depolarising. Suxamethonium is the only commonly used depolarising agent. It acts rapidly and has a short duration, which is why it has traditionally been the agent of choice for rapid sequence induction. The label dose is an average of 0.6 mg/kg intravenously for adults, with an optimum range of 0.3 to 1.1 mg/kg; for infants and small children 2 mg/kg, and for older children and adolescents 1 mg/kg. ^[8] Onset is less than one minute and single-dose duration approximately four to six minutes. ^[8] Suxamethonium releases potassium and is contraindicated after the acute phase of burns, major trauma, extensive denervation or upper motor neuron injury; it can trigger malignant hyperthermia in susceptible patients. ^{[8] [1]}

Non-depolarising agents include rocuronium, vecuronium, atracurium, cisatracurium, mivacurium and pancuronium. Rocuronium at 1.2 mg/kg gives onset and intubating conditions that are comparable to suxamethonium in many studies, and its effect can be reversed rapidly with sugammadex. ^[1] The drugs differ in onset, duration, elimination (organ-dependent or Hofmann elimination) and side effects such as histamine release or hypotension, so the choice follows the patient's cardiac, hepatic and renal function rather than a single rule.

Reversal is checked with a peripheral nerve stimulator, ideally train-of-four monitoring, even when a reversal drug has been given. Sugammadex reverses rocuronium and vecuronium: 2 mg/kg when there are two twitches to train-of-four stimulation, 4 mg/kg when there are 1 to 2 post-tetanic counts with no twitch response, and 16 mg/kg if reversal is needed approximately three minutes after a single dose of 1.2 mg/kg rocuronium. ^[11] Neostigmine with glycopyrrolate remains a common reversal agent for non-depolarising block; atropine is used where vagal effects need control. Neostigmine does not reverse suxamethonium and should not be given while phase one block is present.

Rapid sequence induction is the technique used to secure the airway in a patient with a full stomach or a high risk of aspiration. The aim is to move from consciousness to a cuffed tracheal tube without bag-mask ventilation, so that the airway is protected during the vulnerable interval. Steps:

1. Preoxygenate until the end-tidal oxygen fraction reaches 0.87 to 0.9. In healthy adults the apnoea time without desaturation is 1 to 2 minutes on room air but can be extended to 8 minutes with proper preoxygenation; high-flow nasal oxygen at up to 15 L/min and humidified high-flow at up to 70 L/min extend this further in high-risk patients. ^[1]
2. Position the patient head-up 20 to 25 degrees where practical and preoxygenate in that position. ^[1]
3. Give a pre-calculated rapid-onset induction agent and a rapid-onset neuromuscular blocker, usually suxamethonium or rocuronium 1.2 mg/kg, after induction. ^[1]
4. Apply cricoid pressure with 10 N awake and 30 N as consciousness is lost, then, if ventilation becomes difficult, release it under direct vision. ^[1]
5. Ventilate gently with cricoid pressure in place if needed, intubate as soon as the neuromuscular block is deep, and confirm the position by visualising the tube through the cords plus a continuous carbon dioxide waveform.
6. If intubation fails, follow the difficult airway plan below rather than repeating the same manoeuvre.

Gentle mask ventilation after cricoid pressure and before intubation prolongs the time to desaturation and may be the safer choice in poor respiratory reserve, sepsis or high metabolic demand. It also gives an early sign of how easy ventilation will be. ^[1]

Unanticipated difficult intubation should be managed with a single, rehearsed algorithm rather than with improvised steps. The DAS 2015 guideline provides that algorithm and recommends a maximum of three attempts at laryngoscopy, with a fourth attempt by a more experienced colleague; the same algorithm covers routine intubation and rapid sequence induction. ^[1] The ASA 2022 guidelines present an updated, multi-society consensus report on the management of the difficult airway and are the reference most commonly used alongside DAS 2015. ^[2]

Key points from DAS 2015 that are easy to forget: plan for failed intubation before induction, especially for urgent surgery; emphasise assessment, positioning, preoxygenation, maintenance of oxygenation and minimising trauma; blind passage of bougies or tubes through supraglottic airways is superseded by video- or fibre-optically guided intubation; when both tracheal intubation and supraglottic airway insertion have failed, waking the patient is the default; and if face-mask oxygenation is impossible in the presence of muscle relaxation, cricothyroidotomy should follow immediately. ^[1] Repeat intubation attempts without changing something are only likely to increase trauma. ^[1]

The ASA 2022 algorithm organises assessment, preparation, intubation strategy and rescue in a similar way, with more emphasis on awake (topicalised) techniques, on flexible scope intubation as a first or rescue technique, and on human factors. The two guidelines differ in detail and in emphasis; the ASA document is endorsed by a long list of airway societies, while DAS 2015 is a single, very short, single-page algorithm that is easy to rehearse. Both are worth knowing. ^{[1] [2]}

Monitoring during a general anaesthetic should follow the standards of the unit you work in. As a minimum, continuous ECG, pulse oximetry and capnography plus intermittent non-invasive blood pressure are used in almost all settings; temperature, neuromuscular block and depth of anaesthesia are added when needed; and an arterial line and central line are added when the operation or the patient requires them. Keep the patient warm: inadvertent hypothermia worsens coagulation, drug metabolism, wound infection and recovery. Pressure areas, eyes and peripheral nerves need protection for procedures that outlast a few minutes. Documentation should record depth of anaesthesia and any awareness during critical periods. Postoperative monitoring continues until the patient is fit to leave the recovery area.

Malignant hyperthermia is a hereditary pharmacogenetic disorder of skeletal muscle that presents as a hypermetabolic response to halogenated anaesthetic agents or to the depolarising muscle relaxant succinylcholine. The classic signs are an early onset of hyperthermia, hypercarbia, muscle rigidity and acidosis after exposure to a trigger, with potential complications of rhabdomyolysis, acute kidney injury, coagulopathy and multi-organ failure. ^{[4] [10]} RYR1 and CACNA1S variants are associated with susceptibility. ^[10]

Management is to stop the trigger, give 100% oxygen, hyperventilate, cool the patient, correct acidosis and hyperkalaemia, give fluids and dantrolene intravenously. ^[1] Dantrolene is given as a continuous rapid intravenous push, starting at a minimum dose of 1 mg/kg and continuing until symptoms subside or a cumulative maximum of 10 mg/kg is reached; the prophylactic dose before anticipated anaesthesia in a known susceptible patient is 2.5 mg/kg infused over about one hour. ^[9] Dantrolene must be available wherever triggers are used; rapid administration can be lifesaving. ^{[4] [9]} Genetic susceptibility testing and referral of the patient and family are appropriate after any suspected episode.

Postoperative nausea and vomiting is common after general anaesthesia and causes patient dissatisfaction and measurable harm: raised heart rate and blood pressure, wound dehiscence in some settings, aspiration, delayed discharge and readmission. The reported frequency is up to 80% in high-risk populations and up to 30% of the general population. ^[5] Risk factors include female sex, a history of postoperative nausea or vomiting or motion sickness, non-smoking, younger age, opioid analgesia, volatile anaesthetics, long operations, laparoscopic and gynaecological surgery and a higher baseline risk score such as the Apfel score. The most useful protective measures are reducing or avoiding volatile agents and opioids where pain control allows (for example by using a regional block), giving prophylactic antiemetics in moderate and high risk, and, for high risk patients, using more than one drug from different classes (a 5-HT3 antagonist, a corticosteroid, an NK1 antagonist, a dopamine antagonist or an anticholinergic, following local protocol). Give treatment early rather than late, and check for reversible causes such as hypotension, opioid overdose or gastric distension.

Recovery begins when the patient is safe to leave the operating room: airway patent, breathing adequate, circulation stable, temperature normalising, pain addressed and nausea treated. Position the patient in a recovery position until awake, give oxygen, and continue capnographic or at least clinical monitoring. Assess the patient regularly in the post-anaesthesia care unit, including airway patency, pain, nausea, surgical site and drain output, then discharge to the ward or home with written instructions. Do not accept a patient onto a ward until fitness for discharge criteria are met. Reversal of neuromuscular block should be documented by train-of-four monitoring rather than assumed. Nerve blocks and Patient-Controlled Analgesia pumps require secure arrangements before the patient leaves theatre.

Complications of general anaesthesia range from minor and common (sore throat, postoperative nausea, shivering) to severe (hypoxia, aspiration, dental injury, laryngeal or tracheal trauma, anaphylaxis to drugs, malignant hyperthermia, awareness, major cardiovascular events and neurological injury). Most severe complications are rare, and many are preventable by systematic preparation: checking the anaesthetic machine, preparing the airway, assessing the fasting state, maintaining adequate depth of anaesthesia with appropriate monitoring and responding to change early. When something goes wrong, call for help, declare the problem clearly, and follow the relevant guideline or checklist rather than improvising alone.

In children, airway anatomy, drug dosing and risk of emergence delirium differ, and smooth induction with the child in the parent's presence is common. In pregnancy, airway oedema, aspiration risk and the physiology of the second and third trimesters alter both assessment and management. In older adults, drug sensitivity and organ function require dose reduction and slower titration. Patients with obesity need ramped positioning, preoxygenation in the sitting or head-up position and shorter apnoea times. Patients with neuromuscular disease need care with depolarising blockers and avoidance of succinylcholine. Cultural and low-resource settings: adapt every step to available monitors, drugs and rescue devices, but do not drop the universal steps of preoxygenation, suction, capnographic confirmation of tube position where possible, and a rehearsed failed-intubation plan.

No verified MedGrasp topics are linked yet; relevant future topics will include anaesthetic pharmacology, consent and pre-assessment, paediatric anaesthesia, pharmacology of opioids and postoperative analgesia, and the pharmacology of neuromuscular blockade. These will be linked as plain text titles rather than Topics links, as the current task requires.

• General anaesthesia combines unconsciousness, analgesia, muscle relaxation and autonomic control as separate, titrated components.
• Preoxygenate everyone before induction, aiming for an end-tidal oxygen fraction of 0.87 to 0.9; healthy adults then have up to 8 minutes of apnoea time without desaturation, rather than 1 to 2 minutes on room air.
• Assessment predicts difficulty but does not eliminate it; always have a plan for unexpected difficulty.
• Rapid sequence induction uses a rapid-onset hypnotic and either suxamethonium or rocuronium 1.2 mg/kg with cricoid pressure at 10 N awake and 30 N after loss of consciousness. ^[1]
• Propofol is the default induction agent for most healthy adults, at 2 to 2.5 mg/kg; reduce the dose in elderly, frail, ASA-PS III or IV and cardiac patients. ^[7]
• Capped attempts: DAS 2015 recommends a maximum of three laryngoscopy attempts, a fourth by a more experienced colleague, then a supraglottic airway, then waking or a scalpel cricothyroidotomy in CICO.
• Confirm the tube with a continuous capnography waveform and visualise the cords.
• Managing malignant hyperthermia is stopping the trigger, supporting the patient, and giving dantrolene from 1 mg/kg intravenously up to a cumulative 10 mg/kg; prophylaxis is 2.5 mg/kg.
• Postoperative nausea and vomiting affects up to 80% of high-risk patients and up to 30% of all patients; reduce triggers and give prophylactic antiemetics in moderate and high risk.
• Both DAS 2015 and ASA 2022 should be familiar, but the algorithm that is rehearsed locally is the one that saves lives in a crisis.