Local anesthetic systemic toxicity during a brachial plexus block
A 45-year-old man (70 kg) undergoes an ultrasound-guided interscalene brachial plexus block for shoulder arthroscopy. The anesthetist uses 30 mL of 0.5% bupivacaine with 1:200,000 adrenaline. Ten minutes after injection, the patient becomes agitated, reports tinnitus and a metallic taste, then has a generalized tonic-clonic seizure. He is not yet intubated; the surgeon has not started.
1. Calculate the dose given and explain why this patient developed toxicity despite adrenaline.
Read the worked answer
Dose: 30 mL × 0.5% = 30 × 5 mg/mL = 150 mg bupivacaine. For a 70 kg patient that is 2.1 mg/kg - within the commonly quoted maximum of 2–2.5 mg/kg, but close to the ceiling, and bupivacaine is the most cardiotoxic local anesthetic.
Why toxicity occurred despite adrenaline:
- Adrenaline delays absorption but does not prevent systemic uptake, especially with a highly vascular interscalene site.
- Inadvertent intravascular injection is the most likely cause - the needle tip may have been in a vessel despite negative aspiration.
- Individual variability in protein binding and clearance, and the use of a high concentration near the maximum dose, lower the threshold.
- The interscalene region is close to the vertebral artery and carotid; even small intravascular volumes can cause CNS symptoms.
Lesson: use the lowest effective dose, aspirate before and during injection, inject incrementally with ultrasound, and consider lipid emulsion availability.
2. What is your immediate management, including the specific lipid emulsion regimen?
Read the worked answer
- Stop the injection and call for help; start CPR if the patient arrests.
- Airway - the patient is seizing and not intubated: secure the airway with rapid sequence induction (avoid suxamethonium if hyperkalemia risk, but it is generally acceptable), 100% oxygen, and ventilate.
- Control seizures - benzodiazepine (e.g., midazolam 2–5 mg IV) or propofol; avoid large doses of propofol if cardiovascular instability.
- Lipid emulsion 20% - bolus 1.5 mL/kg (≈100 mL for 70 kg) over 1 minute, then infusion 0.25 mL/kg/min (≈17 mL/min). Repeat bolus if unstable; increase infusion to 0.5 mL/kg/min if refractory. Maximum approximately 10–12 mL/kg over 30 minutes.
- Avoid vasopressin, calcium channel blockers, beta-blockers, and local anesthetics (including lidocaine) during resuscitation.
- Cardiopulmonary bypass/ECMO if refractory.
- Monitor for at least 4–6 hours after stabilization; watch for rebound toxicity.
3. What system changes would you recommend to reduce this event in future?
Read the worked answer
- Standardize maximum doses and display a weight-based dose chart in every block room.
- Incremental injection with aspiration every 3–5 mL and ultrasound visualization of spread.
- Use lower concentrations/volumes where evidence supports (e.g., 0.25% bupivacaine for interscalene).
- Lipid emulsion immediately available in every location where blocks are performed, with a posted regimen.
- Simulation training for LAST and regular team drills.
- Documentation of dose, site, and any aspiration findings.
- Audit of block complications and a morbidity and mortality review.
- Consider adjuncts (dexmedetomidine, dexamethasone) to reduce local anesthetic dose.