01Core principlesThe concepts and mechanisms needed to understand the subject.
Anaesthetic crises are uncommon but evolve quickly while normal communication and examination are limited. A disciplined first response prevents fixation: announce the problem, call for skilled help, give 100% oxygen, verify airway and effective ventilation, assess circulation, stop likely triggers and ask someone to open the appropriate Quick Reference Handbook card. The team should name a leader, allocate tasks, repeat observations and record doses and times.
Laryngospasm is reflex closure of the vocal cords, often around induction or emergence when airway stimulation occurs at an inadequate anaesthetic depth. Partial obstruction may produce stridor; complete obstruction can be silent despite strong inspiratory effort. Treatment removes the stimulus, opens the airway and applies continuous positive pressure with oxygen. Persistent obstruction requires deepening anaesthesia and a neuromuscular blocker, followed by tracheal intubation when necessary.
Perioperative anaphylaxis may present mainly as cardiovascular collapse or bronchospasm because skin signs are hidden or absent. In trained anaesthetic practice with intravenous access and continuous monitoring, the QRH uses titrated intravenous adrenaline for hypotension, together with rapid fluid. This specialist regimen must not be exported to an unmonitored community setting, where intramuscular adrenaline is first-line. After stabilisation, obtain timed tryptase samples, document every exposure and refer for specialist investigation.
Malignant hyperthermia is a pharmacogenetic hypermetabolic reaction triggered by potent volatile agents or suxamethonium in susceptible people. A rapid unexplained carbon dioxide rise and tachycardia are earlier clues than fever. Immediate trigger removal, high-flow oxygen and dantrolene are decisive. Continued acidosis, hyperkalaemia, arrhythmia, rhabdomyolysis and recurrent hypermetabolism require critical-care monitoring and specialist referral.
Key points
- For perioperative anaphylaxis, stop the suspected trigger, call for help, give 100% oxygen, treat profound hypotension with intravenous adrenaline in trained anaesthetic practice and rapid intravenous fluid, then start an infusion if boluses are insufficient. In this monitored adult perioperative setting, start CPR if systolic blood pressure is below 50 mmHg or cardiac arrest occurs.
- For malignant hyperthermia, stop volatile anaesthetics and suxamethonium, give 100% oxygen at maximum flow, hyperventilate, summon dantrolene and the MH pack, and begin active cooling when indicated.
- For laryngospasm, remove the stimulus, call for help, apply jaw thrust and continuous positive airway pressure with 100% oxygen, deepen anaesthesia and use neuromuscular blockade with tracheal intubation if obstruction persists.
- During any crisis, check oxygen supply, circuit, airway, capnography, pulse, blood pressure, surgical field and recently administered drugs while allocating roles and recording events.
- Use the Quick Reference Handbook as a live cognitive aid and calculate emergency drugs aloud with an independent check where time permits.
- The intravenous adrenaline regimen described here is for trained adult perioperative teams; general or community anaphylaxis uses intramuscular adrenaline first, and paediatric and obstetric doses require their own algorithms.
02Mechanisms and patternsImportant relationships and how to distinguish them.
Stridor, tracheal tug, paradoxical chest movement, absent airflow or silent inspiratory effort near airway stimulation indicates partial or complete obstruction.
Unexpected hypotension, bronchospasm, tachycardia or bradycardia after a drug or material exposure can occur without visible rash.
Unexplained rising end-tidal carbon dioxide, tachycardia, increased oxygen consumption and rigidity precede a potentially late temperature rise.
Hypotension, tachycardia, falling end-tidal carbon dioxide, pallor, surgical loss or poor perfusion requires haemorrhage control and balanced resuscitation.
Loss of waveform, high airway pressure or inadequate chest movement requires checking the patient, tube, circuit, filters and gas supply directly.
Loss of a central pulse or an organised rhythm without output activates immediate CPR, defibrillation where indicated and reversible-cause treatment.
03Interpreting evidenceInformation, measurements and their limitations.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Waveform capnography - Why
- Track ventilation and circulation and identify rapid carbon dioxide rise, obstruction, disconnection or loss of output.
- Interpretation and limitations
- A rising trace supports hypermetabolism or hypoventilation in context; an absent trace can reflect apnoea, disconnection, tube displacement or arrest and demands immediate checks.
- 02
Acute serum tryptase - Why
- Support later investigation of suspected perioperative anaphylaxis.
- Interpretation and limitations
- After initial stabilisation, obtain serum tryptase once stable, request a further sample 1–4 hours after symptom onset and obtain a baseline at least 24 hours later. Sampling must not delay resuscitation; a normal result does not by itself exclude anaphylaxis.
- 03
Blood gas with potassium and lactate - Why
- Assess oxygenation, ventilation, metabolic acidosis, hyperkalaemia and tissue perfusion during a major crisis.
- Interpretation and limitations
- Malignant hyperthermia can produce mixed acidosis and hyperkalaemia; repeat values guide resuscitation but treatment starts from clinical recognition.
- 04
Core temperature - Why
- Detect and trend hyperthermia during suspected malignant hyperthermia and guide cooling.
- Interpretation and limitations
- A normal early value does not rule out malignant hyperthermia because temperature rise can be late.
- 05
Exposure and anaesthetic timeline - Why
- Relate deterioration to administered drugs, blood products, antiseptics, antibiotics, latex, airway events and volatile-agent exposure.
- Interpretation and limitations
- A precise timeline guides trigger withdrawal, subsequent allergy investigation and avoidance advice; do not guess the culprit from timing alone.
04Applied reasoningWorked examples connecting principles to decisions.
01Worked case: perioperative collapseSudden hypotension and bronchospasm after inductionMinutes after induction drugs and an antibiotic, blood pressure collapses and airway pressure rises with poor gas exchange.+
- 1Declare suspected perioperative anaphylaxis, call for help, stop suspected triggers, give 100% oxygen, secure the airway and confirm effective ventilation while pausing surgery if possible.
- 2In a trained adult anaesthetic setting, give titrated intravenous adrenaline for hypotension and rapid intravenous crystalloid, escalating to an adrenaline infusion if repeated boluses are ineffective.
- 3In the monitored adult perioperative setting, start immediate CPR if systolic blood pressure is below 50 mmHg or cardiac arrest occurs, follow the perioperative anaphylaxis or ALS algorithm, and reassess alternative causes including tube obstruction, haemorrhage and tension pneumothorax.
- 4After stabilisation, arrange critical-care observation as indicated. Take serum tryptase once stable, request another sample 1–4 hours after symptom onset and obtain baseline at least 24 hours later; do not delay resuscitation for sampling. Record all exposures and refer to a specialist anaesthetic allergy service.
02Hypermetabolic crisisRising carbon dioxide and rigidity under volatile anaesthesiaEnd-tidal carbon dioxide rises rapidly despite increased ventilation, with tachycardia and muscle rigidity after suxamethonium and a volatile agent.+
- 1Declare suspected malignant hyperthermia, call for the MH pack and expert help, stop volatile anaesthetic and suxamethonium, and continue with non-triggering intravenous anaesthesia.
- 2Give 100% oxygen at maximum fresh-gas flow, hyperventilate to reduce carbon dioxide, place activated charcoal filters when available and verify effective ventilation from patient movement, waveform and pressures.
- 3Give intravenous dantrolene 2–3 mg/kg promptly, repeat 1 mg/kg about every five minutes until carbon dioxide and temperature fall, and continue beyond 10 mg/kg if the crisis remains responsive but active.
- 4Cool actively when hyperthermic, treat hyperkalaemia and acidosis, avoid calcium-channel blockers with dantrolene, monitor urine and muscle injury, and arrange critical-care surveillance and specialist referral.
03Airway crisisComplete laryngospasm during emergenceAfter airway stimulation the patient makes strong inspiratory efforts with no airflow and rapidly desaturates.+
- 1Call for help, stop the stimulus, remove airway irritants where possible, apply jaw thrust and continuous positive airway pressure with 100% oxygen.
- 2Deepen anaesthesia if obstruction persists and give an appropriate neuromuscular blocker promptly when oxygenation is threatened.
- 3Ventilate and intubate as required, confirming actual airflow and gas exchange by chest movement and capnography; then assess aspiration, negative-pressure pulmonary oedema and other mimics.
05Relevant medicines and safetySpecific regimens and precautions where medicines are relevant.
Adrenaline for adult perioperative anaphylaxis
A trained anaesthetist may give 50 micrograms intravenously for anaphylaxis with hypotension, repeating to response; use 500 micrograms intramuscularly if intravenous access is unavailable and start an infusion for poor response.This monitored perioperative intravenous regimen is specialist practice; community and general settings use intramuscular adrenaline first, and paediatric doses differ.
Dantrolene
Give 2–3 mg/kg intravenously immediately, then 1 mg/kg about every five minutes until clinical control; continue if needed even when cumulative dose exceeds 10 mg/kg.Do not delay for confirmatory tests; avoid calcium-channel blockers because dangerous hyperkalaemia and cardiovascular collapse can occur.
Neuromuscular blocker for persistent laryngospasm
Use the locally approved rapid adult dose selected for urgency, intravenous access and the airway plan.Paralysis commits the team to effective ventilation and often intubation; confirm ventilation clinically and with waveform capnography.
06Checking understandingVerify the reasoning, revisit uncertainties and apply feedback.
- Use continuous ECG, pulse oximetry, blood pressure and waveform capnography during a crisis, while repeatedly checking the patient and equipment directly.
- Trend end-tidal carbon dioxide, core temperature, potassium, acid-base state, lactate and urine output during and after malignant hyperthermia treatment.
- During anaphylaxis, repeat haemodynamics after each adrenaline and fluid intervention and record exact exposure, onset, dose and response times.
- After laryngospasm, continue observation for recurrent obstruction, aspiration and negative-pressure pulmonary oedema rather than ending monitoring when saturation first recovers.
- Use critical-care monitoring after severe events because biphasic anaphylaxis, recurrent hypermetabolism, rhabdomyolysis or organ injury may emerge later.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Skin signs may be absent
Covered skin and profound shock can make perioperative anaphylaxis present as unexplained hypotension or bronchospasm alone.
Temperature can be late
Waiting for fever can delay malignant-hyperthermia treatment when carbon dioxide and tachycardia are already rising.
A silent airway can be closed
Complete laryngospasm may produce no stridor because no gas passes the cords.
A waveform is evidence, not a guarantee
Ventilation requires correlation of capnography with chest movement, pressures, leaks and circulation during rescue.
Debrief follows survival
Accurate records, patient explanation, referrals and team review prevent a successfully treated emergency becoming a repeated hazard.
08Common pitfallsFrequent interpretation and management errors.
- 01
Waiting for a rash before treating otherwise unexplained perioperative cardiovascular collapse as anaphylaxis.
- 02
Applying specialist intravenous perioperative adrenaline dosing to an unmonitored community setting.
- 03
Waiting for high temperature before stopping triggers and giving dantrolene in a hypermetabolic crisis.
- 04
Continuing repeated airway manoeuvres while persistent laryngospasm causes rapidly worsening hypoxaemia.
- 05
Assuming selected ventilation settings prove effective gas movement without checking the patient and waveform.
- 06
Ending care after immediate recovery without tryptase sampling, critical-care planning or specialist referral.