Agitation and Seizure 20 Minutes After an Interscalene Block

This is local anesthetic systemic toxicity (LAST). The sequence - perioral numbness, tinnitus, agitation, then a generalized seizure 20 minutes after injection - is the classic excitatory prodrome. The timing fits: vascular uptake peaks within minutes to tens of minutes, and delayed presentations occur.

The dose math: 20 mL of 0.5% = 100 mg bupivacaine; 100 mg ÷ 82 kg = 1.2 mg/kg. Commonly cited ceilings are roughly 2 mg/kg without and 3 mg/kg with epinephrine, so this dose was within conventional limits.

That single fact should change your reasoning: LAST is not a dosing violation, it is an intravascular or rapid-uptake event. The interscalene region is highly vascular, a needle tip can enter the cervical vasculature even under ultrasound, and a negative aspiration does not exclude intravascular placement. Bupivacaine is also the most cardiotoxic of the common agents, so the threshold for action is low.

Exclude mimics quickly: glucose 104 rules out hypoglycemia; no seizure history; anxiety/hyperventilation can cause perioral tingling but not a true generalized seizure; the epinephrine in the solution explains some of the hypertension and tachycardia but not the neurologic progression.

1. Call for help and announce LAST. Someone fetches the lipid emulsion and the ASRA checklist.
2. 100% oxygen by mask, support ventilation. Hypoxia, hypercarbia, and acidosis all worsen toxicity and lower the seizure threshold.
3. Terminate the seizure: midazolam 2–4 mg IV in small aliquots. If it persists, a small induction dose of propofol is acceptable in a hemodynamically stable patient - avoid it if pressure is falling.
4. Give lipid emulsion early, not as a last resort: 20% emulsion 1.5 mL/kg ≈ 120 mL bolus over 1 minute, then an infusion of 0.25 mL/kg/min ≈ 20 mL/min. Repeat the bolus and double the infusion if he remains unstable. Commonly cited cumulative ceiling is about 10 mL/kg over 30 minutes.
5. Prepare for arrhythmia: amiodarone is preferred for local-anesthetic-induced ventricular arrhythmia. Do not give lidocaine. Avoid vasopressin, beta blockers, and calcium channel blockers. If vasopressors are needed, use epinephrine in small boluses (≤1 mcg/kg).
6. If he arrests: start CPR early, expect a longer resuscitation, and call for cardiopulmonary bypass or ECMO early.

Cancel the case. He has just had a generalized seizure and a systemic toxic exposure to a cardiotoxic agent. Even after full recovery, bupivacaine toxicity can recur; he needs monitored observation (commonly at least 4–6 hours, or overnight with telemetry) and reassessment of electrolytes and acid-base status. Proceeding would add surgical stimulus, bleeding, and another anesthetic on top of a recent seizure - no elective arthroscopy justifies that.

Next time, change the technique, not just the dose:

• Use less drug: 10–15 mL at the lowest effective concentration (0.25–0.375% for an arthroscopic shoulder is often sufficient). Lower volume also reduces phrenic spread.
• Keep the needle tip visible at all times under ultrasound and inject incrementally in small aliquots with frequent aspiration; avoid high-pressure injection.
• Do not rely on a test dose in the brachial plexus - epinephrine markers are unreliable there.
• Have lipid emulsion physically present in any area where large-volume blocks are performed, and rehearse the checklist.
• Consider whether an interscalene block was even indicated for a procedure that may be done with a lower-risk distal block plus multimodal analgesia.