01Core principlesThe concepts and mechanisms needed to understand the subject.
General anaesthesia is not a single injection or vapour concentration. It is a sequence of controlled transitions in consciousness, airway tone, ventilation, circulation and nociceptive response. Hypnotic agents produce unconsciousness and amnesia; opioids, regional blocks and non-opioid analgesics attenuate pain; neuromuscular blockers create immobility and facilitate airway or surgery but provide neither anaesthesia nor analgesia. Volatile agents or intravenous infusions maintain hypnosis. Each component is titrated to the person, procedure, physiological response and monitoring rather than inferred from immobility alone.
Preparation prevents predictable crises. Review the surgical plan, urgency, expected duration, position, stimulation, blood loss and postoperative needs. Confirm allergies and previous anaphylaxis, airway and anaesthetic history, fasting and aspiration factors, comorbidity, medicines, pregnancy possibility where relevant, consent and resuscitation or escalation decisions. Check oxygen supplies, breathing system, suction, ventilator, infusion devices, airway and rescue equipment, monitoring and emergency drugs. A dedicated trained assistant must be immediately available wherever anaesthesia care is delivered.
Induction deliberately removes protective reflexes and often spontaneous ventilation. Apply monitors first, establish reliable IV access, preoxygenate or otherwise provide continuous oxygen, position the patient and brief the team. Select an induction method that fits cardiovascular reserve, aspiration risk, airway strategy and surgical need. Confirm effective facemask ventilation where appropriate, ensure adequate neuromuscular block before intubation when a blocker is used, and confirm any tracheal tube with visual passage plus sustained waveform capnography. A flat trace is an emergency signal, not a reason to wait for desaturation.
Maintenance has four parallel tasks. Deliver enough hypnotic and analgesic effect for the changing stimulus; ventilate and oxygenate without excessive pressure or volume; maintain perfusion, temperature, glucose and fluid balance; and protect the patient from positioning, pressure, eye, nerve and device injury. The anaesthetist remains present and continually assesses the patient. Alarms are set to patient-specific values and remain audible. Monitoring adds information but never replaces observation of the patient, surgical field, reservoir bag, airway and equipment.
Technique-specific monitoring closes predictable blind spots. During inhalational anaesthesia, monitor inspired and end-tidal agent concentration and age-adjusted MAC. With mechanical ventilation, monitor airway pressure, tidal volume and respiratory rate. With any neuromuscular blocker, use quantitative monitoring from before blockade to objective recovery above 0.9. With TIVA plus neuromuscular block, add processed EEG from before induction until recovery from block; also inspect infusion access and pumps because disconnection may not create a vapour alarm.
Emergence and recovery are high-risk transitions. Plan analgesia and antiemesis before stimulation ends, restore normothermia and physiological stability, and reverse neuromuscular block according to the actual quantitative measurement. Extubate only when the airway strategy, oxygenation, ventilation, consciousness and protective reflexes support it. Continue monitoring through transfer. Give a formal handover covering procedure, anaesthetic, airway, allergies, medicines, fluids and blood, analgesia, antiemetics, complications, current observations and the escalation plan.
The RCoA 2025 adult elective and urgent-care standard keeps anaesthetic responsibility into recovery until discharge or named handover. Care is one-to-one until the patient maintains their airway, communicates and has respiratory and cardiovascular stability. Recovery staff require appropriate competence, oxygen, suction, monitoring and rapid access to airway-skilled help. A patient who remains unstable needs continued anaesthetic assessment and a destination capable of the necessary support.
Key points
- General anaesthesia is a titrated state combining unconsciousness, amnesia, analgesia and immobility while preserving oxygen delivery, ventilation and organ perfusion; the required balance changes throughout the operation.
- Before induction, confirm identity, consent and procedure, fasting and aspiration risk, allergies, medicines, airway plan, equipment checks, monitoring, IV access, positioning, blood-loss plan and postoperative destination.
- Core monitoring in all cases includes ECG, non-invasive blood pressure, pulse oximetry and temperature, measured before anaesthesia and every 30 minutes until surgery ends. General anaesthesia adds inspired and expired oxygen and waveform capnography; add agent concentration if inhalational anaesthesia is used, pressure-volume-rate monitoring during mechanical ventilation, quantitative monitoring whenever neuromuscular block is used, and processed EEG for TIVA with neuromuscular block.
- Waveform capnography should run uninterrupted from induction and airway insertion through maintenance, transfer and emergence until an artificial airway is removed and verbal contact is restored.
- Whenever a neuromuscular blocking drug is used, quantitative monitoring starts before blockade and continues until a train-of-four ratio above 0.9 is documented before awakening and extubation.
- Recovery is active anaesthetic care: formal handover, continuous observation, airway and physiological stability, treatment of pain and nausea, and a clear escalation or discharge destination are required.
02Mechanisms and patternsImportant relationships and how to distinguish them.
Movement, lacrimation, sweating, tachycardia or hypertension may reflect stimulation, but also hypovolaemia, hypoxia, hypercapnia or equipment failure; interpret signs with technique and monitoring.
Changed capnogram, airway pressure, expired volume, chest movement, reservoir-bag behaviour or oxygen saturation may reveal disconnection, obstruction, leak, displacement or bronchospasm.
Hypotension after induction can result from vasodilation, reduced preload, myocardial depression, anaphylaxis or bleeding; treat the physiology and cause rather than a monitor number alone.
Weak breathing, airway obstruction, impaired swallow or low tidal volume may persist despite apparent movement; qualitative twitch or clinical tests cannot replace a quantitative train-of-four ratio.
Consider ongoing anaesthetic or opioid effect, residual paralysis, hypothermia, hypoglycaemia, hypercapnia, electrolyte disturbance, organ dysfunction and neurological injury in a structured sequence.
Obstruction, laryngospasm, hypoventilation, bleeding, hypotension, arrhythmia, severe pain, agitation or reduced consciousness requires immediate ABCDE review and anaesthetic help.
03Interpreting evidenceInformation, measurements and their limitations.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Waveform capnography - Why
- Confirm airway ventilation and follow patency and alveolar ventilation continuously.
- Interpretation and limitations
- A sustained waveform after intubation supports tracheal ventilation. A flat capnogram indicates oesophageal intubation until excluded; abrupt later loss prompts immediate assessment for disconnection, displacement, obstruction or absent circulation.
- 02
Core physiological monitoring - Why
- Track oxygenation, circulation and temperature throughout anaesthesia and recovery.
- Interpretation and limitations
- ECG, pulse oximetry, NIBP and temperature are core monitoring in all cases. Measure temperature before anaesthesia and every 30 minutes until surgery ends; measure NIBP at least every five minutes during anaesthesia, with shorter intervals or invasive assessment when physiology demands.
- 03
Quantitative neuromuscular monitoring - Why
- Measure onset, depth and recovery whenever a neuromuscular blocking drug is administered.
- Interpretation and limitations
- Apply before blockade and use through all phases; document train-of-four ratio above 0.9 before awakening and extubation rather than relying on head lift or visible twitch.
- 04
Agent and processed EEG monitoring - Why
- Identify inadequate or excessive hypnotic delivery and detect infusion interruption where appropriate.
- Interpretation and limitations
- Use age-adjusted MAC with volatile agents. Use processed EEG with TIVA plus neuromuscular blockade and consider it for high-risk patients or other techniques; interpret values with drug delivery and clinical context.
- 05
Blood gas, haemoglobin and glucose - Why
- Answer specific questions about ventilation, oxygen delivery, bleeding or metabolic disturbance during higher-risk care.
- Interpretation and limitations
- Use results with trends and sampling context. Blood gas analysis and haemoglobin measurement should be accessible; treated diabetes requires at least hourly glucose measurement under the monitoring guideline.
04Applied reasoningWorked examples connecting principles to decisions.
01Worked case: uncomplicated adult general anaesthesiaElective laparoscopic procedure from induction to recoveryA stable adult has completed preoperative assessment and is scheduled for an elective operation requiring general anaesthesia and tracheal intubation.+
- 1Confirm patient, procedure, consent, allergies, fasting, aspiration and airway plan, comorbidity and medicine instructions; brief the trained assistant, check machine, circuit, suction, airway rescue equipment, infusions and postoperative destination.
- 2Attach ECG, pulse oximetry and NIBP, measure temperature, establish IV access, start inspired and expired oxygen monitoring and waveform capnography, preoxygenate and optimise position and haemodynamics before induction.
- 3Induce with a technique selected for physiology and aspiration risk, ensure adequate anaesthetic depth and neuromuscular blockade where used, perform the planned airway manoeuvre and confirm tracheal ventilation visually and with a sustained capnogram.
- 4Maintain hypnosis, analgesia, oxygenation, ventilation, perfusion and temperature; monitor agent delivery, airway pressure, tidal volume, respiratory rate and quantitative neuromuscular function as applicable, and reassess after positioning or surgical changes.
- 5Plan emergence before closure, establish analgesia and antiemesis, confirm train-of-four ratio above 0.9 after any neuromuscular blocker, and extubate only when ventilation, oxygenation, airway protection and the rescue plan are satisfactory.
- 6Continue appropriate monitoring during transfer, provide a structured recovery handover, and retain responsibility until stable discharge from recovery or explicit transfer to another named clinician.
02Absent carbon-dioxide traceFlat capnogram after tracheal intubationThe tracheal tube appears to pass through the cords, but ventilation produces no sustained waveform capnogram.+
- 1Treat the flat trace as oesophageal intubation until excluded, call for help, deliver oxygen and assess the patient, tube, capnography sampling system and breathing circuit without waiting for saturation to fall.
- 2If tracheal placement cannot be promptly established with reliable evidence, remove the misplaced or unconfirmed tube and restore facemask oxygenation using the adult difficult-airway strategy as required.
- 3Reattempt airway management only after oxygenation, equipment function, position, operator and the next technique have been optimised, then require visual and capnographic confirmation again.
03Neuromuscular recoverySafe reversal and extubationA neuromuscular blocking drug has been used and the operation is finishing.+
- 1Use the quantitative monitor throughout anaesthesia and identify the actual depth and trend of block before choosing the timing and method of reversal.
- 2Continue ventilation, anaesthesia and observation while recovery occurs; do not substitute sustained head lift, tidal volume or qualitative fade for objective measurement.
- 3Confirm and document train-of-four ratio above 0.9 before awakening and extubation, then continue to observe ventilation and airway patency in recovery.
04Recovery deteriorationReduced consciousness and hypoventilationIn PACU an adult remains drowsy with shallow breathing and declining oxygen saturation after general anaesthesia.+
- 1Call the anaesthetist and perform an immediate ABCDE assessment, opening the airway, delivering oxygen and supporting ventilation while reviewing capnography and neuromuscular data.
- 2Check for obstruction, residual block, opioid or hypnotic effect, hypercapnia, hypothermia, hypoglycaemia, bleeding and haemodynamic or neurological causes, treating the identified cause with monitored support.
- 3Continue one-to-one care and do not transfer onward until the patient maintains their airway, communicates appropriately and has respiratory and cardiovascular stability or is moved to an appropriate higher-acuity destination.
05Checking understandingVerify the reasoning, revisit uncertainties and apply feedback.
- An anaesthetist remains present throughout general anaesthesia. In all cases use clinical observation with ECG, pulse oximetry, NIBP and temperature; measure temperature before anaesthesia and every 30 minutes until surgery ends. General anaesthesia also requires inspired and expired oxygen and waveform capnography.
- Record heart rate, blood pressure, oxygen saturation and end-tidal carbon dioxide at least every five minutes on a manual chart, and record additional values when significant changes occur.
- During mechanical ventilation, display airway pressure and monitor tidal volume and respiratory rate; set high- and low-pressure and volume alarms for the individual patient and mode.
- For inhalational anaesthesia, monitor inspired and end-tidal volatile concentration and age-adjusted MAC; for TIVA with neuromuscular block, monitor infusion delivery, quantitative block and processed EEG.
- Continue monitoring during transfer and recovery, including capnography while an artificial airway remains, and repeat airway, respiratory, cardiovascular, consciousness, pain, nausea and temperature assessments after handover.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Immobility is ambiguous
A paralysed patient cannot signal inadequate hypnosis by movement, so drug-delivery checks, agent or processed EEG monitoring and physiological interpretation become especially important.
Capnography spans transitions
Induction, repositioning, transfer and emergence are common times for displacement or disconnection; uninterrupted waveform monitoring closes the gaps created by movement and handover.
Alarms require ownership
Audible alarms should remain enabled and limits must fit the patient and technique. Silencing a recurring alarm without finding its cause removes an early warning system.
Block needs measurement
Dose timing and visible movement do not prove recovery. Objective train-of-four monitoring above 0.9 addresses weakness that bedside tests can miss.
TIVA has distinct failure modes
A disconnected cannula or interrupted infusion can cause awareness without a low volatile-agent alarm; visible access, enabled pump alarms and processed EEG when paralysed reduce this risk.
Recovery remains anaesthesia
Airway tone, ventilation, haemodynamics, temperature and drug effects evolve after surgery. Responsibility ends through stable discharge or explicit named handover, not at skin closure.
07Common pitfallsFrequent interpretation and management errors.
- 01
Beginning induction before monitoring, oxygen, suction, airway rescue equipment and a trained assistant are ready.
- 02
Treating neuromuscular blockade as analgesia or assuming immobility proves adequate unconsciousness.
- 03
Ignoring a flat capnogram because the chest appears to rise or breath sounds seem symmetrical.
- 04
Using a fixed induction or maintenance dose without accounting for frailty, physiology, comorbidity and concurrent medicines.
- 05
Extubating on clinical signs alone after neuromuscular blockade without a documented quantitative ratio above 0.9.
- 06
Leaving recovery before formal handover and before airway, respiratory and cardiovascular stability have been established.