General anaesthesia: induction, maintenance and emergence

What it is

General anaesthesia runs in three phases. Induction takes the patient from awake to anaesthetised, usually with an intravenous hypnotic after preoxygenation, or by breathing a volatile agent (inhalational induction, common in children); an opioid is often added and a neuromuscular blocker when the airway will be intubated, and the airway is then secured with a supraglottic device or a tracheal tube. Maintenance keeps the patient anaesthetised for as long as surgery needs, with a volatile agent in oxygen and air or with a continuous intravenous infusion (total intravenous anaesthesia), plus analgesia, muscle relaxation when required, fluids, temperature control and continuous monitoring. Emergence begins when the agents are stopped: the drugs are washed out, neuromuscular block is reversed and its recovery confirmed, spontaneous breathing and airway reflexes return, and the airway device is removed before the patient goes to recovery. The classic stages described by Guedel with ether (analgesia, excitement, surgical anaesthesia, overdose) are seen far less clearly with modern drugs but still explain why patients are vulnerable while passing through the excitement stage at induction and on emergence: breath-holding, coughing, laryngospasm, vomiting and movement are most likely then. Like the take-off and landing of a flight, induction and emergence carry most of the airway and cardiovascular events.

Key points

• Preoxygenation before induction fills the lungs with oxygen and buys time if the airway is difficult.
• Intravenous induction is fast; inhalational induction avoids a needle in a frightened child and keeps spontaneous breathing.
• Rapid-sequence induction is used when the stomach may be full, to secure the airway as fast as possible.
• Most induction agents cause vasodilation and myocardial depression, so blood pressure falls after induction, especially in the elderly or hypovolaemic.
• Emergence can be awake (protective reflexes back) or, in selected patients, with the airway removed while still deeply anaesthetised to avoid coughing.

Components

• Induction: preoxygenation, hypnotic, often an opioid, a neuromuscular blocker if intubating, then airway securing and confirmation with capnography.
• Maintenance: hypnotic (volatile or intravenous), analgesia, muscle relaxation if needed, ventilation, fluids, warming, positioning and monitoring.
• Emergence: stop the agents, reverse the block, restore spontaneous breathing, remove the airway, hand over in recovery.

How it works

• Volatile agents reach the brain through the lungs: their effect depends on the alveolar concentration, and they are cleared the same way at emergence.
• Intravenous agents act within one arm-to-brain circulation time; their effect ends by redistribution and then metabolism.
• Loss of consciousness removes airway tone and protective reflexes and depresses breathing, which is why the airway must be managed.
• Surgical stimulation raises the anaesthetic needed; too little leads to movement, a stress response or awareness, too much to hypotension.

Step by step

1. Check the patient, consent, fasting, the machine and drugs, and attach the monitors — a safe start depends on all of them.
2. Preoxygenate with a tight-fitting mask — the oxygen reserve delays desaturation if the airway is difficult.
3. Give the induction agent, then confirm loss of consciousness and ventilate by mask — this proves ventilation is possible before paralysis.
4. Secure the airway and confirm the tracheal tube with a sustained capnography trace — clinical signs alone can miss oesophageal intubation.
5. Maintain anaesthesia and analgesia, adjusting to surgical stimulation — depth must follow the operation, not stay fixed.
6. Near the end, plan analgesia and nausea prophylaxis, then stop the agents — so the patient wakes comfortable.
7. Reverse and confirm recovery from neuromuscular block before removing the airway — residual block causes hypoxaemia and aspiration.
8. Remove the airway when reflexes and breathing are adequate, give oxygen and hand over in recovery — emergence problems are common in the first minutes.

Guedel's stages of anaesthesia (described with ether; less distinct with modern drugs)

Next step

• Before induction, run through the airway plan and its backups aloud with the team.
• Treat post-induction hypotension promptly and look for the cause; in frail or hypovolaemic patients choose drugs and pace to avoid it.
• Call a senior anaesthetist at once for difficult ventilation, persistent desaturation or laryngospasm on emergence.
• Do not extubate until neuromuscular recovery is confirmed and the patient breathes adequately with protective reflexes.
• In recovery, monitor breathing, oxygen saturation, pain, nausea and temperature, and discharge only when the unit's criteria are met.

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Elsewhere in DurgiPedia

• Bag-mask ventilation
• Postoperative care on the ward: the first 24–48 hours

Connections

← All of anaesthesia

Educational content; it does not replace supervised training, your institution's protocols or the anaesthetist's or intensivist's decision. It contains no doses and no ventilator or infusion settings.

Sources: Anesthesia Stages (StatPearls (NCBI Bookshelf), 2023); General Anesthesia for Surgeons (StatPearls (NCBI Bookshelf), 2023).

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Representative model, for educational purposes only.