Two rare but lethal anaesthetic emergencies that can present in theatre, recovery or ICU: malignant hyperthermia (stop triggers, dantrolene 2.5 mg/kg, cool, treat hyperkalaemia) and LAST (airway, seizure control, 20% lipid emulsion, modified ACLS).
At the bedside
Timed steps- 1
Suspect malignant hyperthermia
Recognise MHDuring/after volatile anaesthetic or suxamethonium: unexplained rising ETCO₂ despite increased ventilation, tachycardia, masseter or generalised rigidity, mixed metabolic and respiratory acidosis, hyperkalaemia, arrhythmias; hyperthermia is often LATE. Can appear up to hours after exposure.
- 2
Stop triggers, call for help, hyperventilate
MH 0–2 minStop volatile agents and suxamethonium; declare an MH emergency and get the MH kit/dantrolene; 100% O₂ at high fresh-gas flow (≥10 L/min); hyperventilate (2–3 × minute volume); insert activated charcoal filters if available; switch to TIVA if surgery must continue; tell the surgeon to finish quickly.
- 3
Dantrolene
MH ASAP2.5 mg/kg IV bolus (each 20 mg vial needs 60 mL sterile water — assign several people to reconstitute). Repeat every 5–10 min until ETCO₂, HR and temperature settle; most need ≤10 mg/kg but give more if signs persist.
- 4
Cool and treat complications
MHIf temperature >39 °C: cold IV saline, surface cooling, ice packs to groin/axillae; stop cooling at ~38.5 °C. Hyperkalaemia: insulin–glucose, calcium, hyperventilation. Arrhythmias: amiodarone or beta-blocker; avoid calcium-channel blockers with dantrolene. Aim urine output ≥2 mL/kg/h (fluids, consider furosemide) to protect against myoglobinuric AKI.
- 5
ICU for ≥24 h
MH afterMonitor for recrudescence: continue dantrolene 1 mg/kg every 4–6 h (or infusion) for 24 h; check CK, K⁺, myoglobin, coagulation (DIC), renal function. Refer patient and family for MH susceptibility testing (contracture testing/genetic) and give an alert card.
- 6
Suspect local anaesthetic systemic toxicity
Recognise LASTWithin seconds to ~1 h of a block, infiltration or IV lidocaine: perioral numbness, metallic taste, tinnitus, agitation, confusion, seizures, then bradycardia, wide-QRS arrhythmias, hypotension, cardiac arrest (may be the first sign, especially with bupivacaine).
- 7
Stop, call, airway
LAST 0–2 minStop injecting; call for help and the LAST kit; 100% O₂, ventilate to prevent hypoxia and acidosis; treat seizures with a benzodiazepine (avoid large doses of propofol in cardiovascular instability).
- 8
Lipid emulsion 20%
LASTAt the first sign of serious toxicity: >70 kg give 100 mL over 2–3 min then 200–250 mL over 15–20 min; ≤70 kg give 1.5 mL/kg bolus then 0.25 mL/kg/min. Repeat bolus once or twice and/or double infusion if still unstable; upper limit ~12 mL/kg.
- 9
Modified ACLS
LAST arrestSmall adrenaline doses (≤1 mcg/kg); avoid vasopressin, calcium-channel blockers, beta-blockers and local anaesthetics (lidocaine/procainamide) for arrhythmias; prolonged CPR — consider cardiopulmonary bypass/ECMO if available. Monitor ≥4–6 h after cardiovascular toxicity (≥2 h after isolated CNS signs).
MH crisis
Dantrolene sodium
- Dose
- 2.5 mg/kg, repeat every 5–10 min until controlled (usually ≤10 mg/kg); then 1 mg/kg every 4–6 h for 24 h
- Preparation
- 20 mg vial + 60 mL sterile water for injection (no saline/dextrose)
- Worked example
- 70 kg: 175 mg = 9 vials of 20 mg (each in 60 mL sterile water); up to 700 mg = 35 vials.
LAST — first sign of serious toxicity
Lipid emulsion 20% (intravenous fat emulsion)
- Dose
- >70 kg: 100 mL over 2–3 min then 200–250 mL over 15–20 min; ≤70 kg: 1.5 mL/kg then 0.25 mL/kg/min; max ~12 mL/kg
- Worked example
- 60 kg lean weight: bolus 90 mL, then 15 mL/min (≈900 mL/h); 80 kg: 100 mL then 250 mL over 15–20 min.
MH and its mimics
| Condition | Distinguishing features |
|---|---|
| Malignant hyperthermia | Volatile/suxamethonium exposure; rising ETCO₂, rigidity, hyperkalaemia, rapid CK rise |
| Sepsis | Fever, source, slower evolution, no rigidity |
| Thyroid storm | Thyroid history, goitre, AF; ETCO₂ rise less marked; no rigidity |
| Neuroleptic malignant syndrome | Antipsychotic exposure, days of evolution, rigidity, altered mental state |
| Serotonin syndrome | Serotonergic drugs, clonus, hyperreflexia, mydriasis |
| Hypercapnia from equipment | Exhausted soda lime, rebreathing, laparoscopic CO₂ absorption |
| Phaeochromocytoma crisis | Paroxysmal hypertension, tachycardia; no rigidity |
Commonly used maximum local anaesthetic doses (guide only)
| Drug | Plain | With adrenaline |
|---|---|---|
| Lidocaine | 3–4.5 mg/kg (max ~300 mg) | 7 mg/kg (max ~500 mg) |
| Bupivacaine / levobupivacaine | 2–2.5 mg/kg (max ~150–175 mg) | 2.5–3 mg/kg (max ~225 mg) |
| Ropivacaine | 3 mg/kg (max ~200–300 mg) | Similar |
Toxic dose depends on site (intercostal and caudal blocks give highest plasma levels), age, cardiac/hepatic disease and pregnancy. Use ultrasound, incremental injection and aspiration.
References
- 1
- 2
- 3
Suspected malignant hyperthermia
Step 1 of ~5
EMHG/MHAUS-based crisis pathway.
Stop volatiles/suxamethonium; call for help; 100% O₂ ≥10 L/min; hyperventilate
Based on Glahn KPE, Ellis FR, Halsall PJ, et al; Malignant Hyperthermia Association of the United States (MHAUS). Educational use; follow local protocol.
Pathophysiology
In MH, abnormal ryanodine receptors release excess Ca²⁺ from sarcoplasmic reticulum, causing sustained muscle contraction, ATP depletion, CO₂ and heat production, rhabdomyolysis and hyperkalaemia. Dantrolene blocks RYR1 Ca²⁺ release. LAST: sodium-channel blockade in brain (excitation then depression) and heart (conduction block, reduced contractility); lipid emulsion acts as a 'sink' and provides direct cardiotonic/metabolic effects.
Evidence
- EMHG 2010 guideline and MHAUS crisis protocol: immediate trigger removal, hyperventilation with high fresh-gas flow, dantrolene 2.5 mg/kg repeated, active cooling, management of hyperkalaemia and arrhythmias, and post-crisis monitoring and referral.
- Dantrolene introduction reduced MH mortality from historical figures of ~70–80% to under 5–10% in centres with prompt treatment.
- ASRA LAST checklist 2020: lipid emulsion dosing simplified by weight (>70 kg fixed 100 mL bolus), modified ACLS (small adrenaline doses), prolonged monitoring.
- Lipid emulsion evidence is from animal studies, case series and registries; no RCTs are feasible.
Controversies
- How much dantrolene to stock in hospitals with infrequent volatile use (cost vs risk).
- Lipid emulsion for non-local-anaesthetic lipophilic drug overdose (e.g. some calcium-channel blockers) — weak evidence, interferes with lab tests and ECMO circuits.
🇮🇳 India notes
- Dantrolene is expensive and often not stocked in Indian hospitals; many units rely on borrowing from nearby centres — know your nearest supply in advance. MH-susceptibility testing (contracture tests) is not widely available in India; genetic testing may be accessible through private laboratories.
- Suxamethonium and halothane/isoflurane remain widely used in India, so MH can present anywhere, including district hospitals.
- Lipid emulsion 20% is usually stocked as parenteral nutrition in pharmacy — keep a dedicated bag in theatre/LAST kit.
- Ultrasound-guided blocks by surgeons and in emergency departments increase LAST exposure outside theatres.
References
- 1
- 2
- 3
Test yourself
Module quiz · score 70% to complete the module
Educational reference for trained clinicians. Check doses against your hospital protocol and the patient in front of you.