Local Anesthetic Systemic Toxicity During Interscalene Brachial Plexus Block

Dose calculation:

• Ropivacaine 0.5% contains 5 mg/mL.
• 40 mL × 5 mg/mL = 200 mg.
• 200 mg ÷ 70 kg = 2.86 mg/kg.

Why toxicity occurred:

• The maximum recommended single dose of ropivacaine is approximately 3 mg/kg, so 2.86 mg/kg is very close to the ceiling. There is little margin for error.
• The interscalene region is highly vascular. A negative aspiration does not exclude intravascular placement, because the needle tip can move or the vessel can be compressed during aspiration.
• Absorption from a vascular plexus is rapid, so toxic concentrations can occur within minutes.
• The patient's symptoms are classic: tinnitus and metallic taste are early central nervous system signs, followed by agitation, seizure, and then cardiovascular toxicity with bradycardia and hypotension.

Reasoning: Ropivacaine is less cardiotoxic than bupivacaine, but it still causes seizures and cardiovascular collapse at high doses. The dose was near the maximum, and the site was high-risk. This is a dose-and-site problem, not necessarily a violation of a arbitrary limit.

Immediate priorities:

1. Stop the injection and call for help.
2. Maintain the airway and give 100% oxygen; the supraglottic airway is already in place.
3. Control the seizure with a benzodiazepine, for example midazolam 2–4 mg IV titrated.
4. Start 20% lipid emulsion immediately.
5. Treat bradycardia and hypotension with small doses of epinephrine, and start an infusion if needed.

Lipid emulsion regimen:

• Bolus: 1.5 mL/kg of 20% lipid emulsion = 1.5 × 70 = 105 mL over about 1 minute.
• Infusion: 0.25 mL/kg/min = 17.5 mL/min, continued for at least 15 minutes after circulatory stability.
• Repeat the bolus once or twice if the patient remains unstable.
• Maximum cumulative dose: approximately 10 mL/kg over 30 minutes.

Additional considerations:

• Avoid lidocaine for arrhythmias.
• Avoid vasopressin, calcium channel blockers, beta blockers, and large doses of epinephrine.
• If cardiac arrest occurs, perform prolonged CPR and consider extracorporeal membrane oxygenation; do not stop resuscitation early.

Reasoning: Lipid emulsion acts as a lipid sink and supports myocardial energetics. It must be given early, alongside standard resuscitation, not after other measures fail.

Preventive changes:

• Use ultrasound guidance in addition to nerve stimulation, because direct visualization reduces but does not eliminate intravascular injection.
• Inject incrementally, aspirating every 3–5 mL, and monitor the patient continuously during injection.
• Reduce the total dose: for interscalene block, 20–30 mL of a lower concentration such as ropivacaine 0.375% is often sufficient for analgesia.
• Avoid using the maximum calculated dose simply because it is below the limit; use the smallest effective volume.
• Consider adding a perineural adjuvant such as dexamethasone to prolong analgesia and allow a lower local anesthetic dose.
• Have lipid emulsion immediately available wherever high-volume blocks are performed.
• Monitor the patient with continuous ECG, pulse oximetry, and blood pressure during and after injection.

Reasoning: The event was likely caused by a combination of a near-maximum dose and a highly vascular injection site. Reducing volume and concentration, injecting slowly under ultrasound, and monitoring for early symptoms are the most reliable safeguards.