Agitation and muscle twitching during sedation for third molar surgery

Working diagnosis: local anaesthetic systemic toxicity (LAST) from articaine.

Supporting features:

• A cumulative dose that exceeds the recommended maximum (see next task) delivered largely into one region over a short period.
• Prodromal symptoms in the classic order - perioral numbness and metallic taste are the earliest excitatory CNS features and are highly suggestive.
• Progression to agitation and fine muscle twitching, which is the excitatory phase that typically precedes seizures.
• Hypertension and tachycardia, consistent with early sympathetic stimulation and with the adrenaline load.

Differential, and why each is less likely:

1. Paradoxical benzodiazepine reaction - gives disinhibition and agitation, but not metallic taste, perioral numbness or perioral twitching; 5 mg midazolam in a 70 kg man is a modest dose.
2. Inadvertent intravascular adrenaline - causes palpitations, tremor and hypertension, but the effects peak within 2–3 minutes and settle; it does not produce perioral numbness or a metallic taste, and the symptoms here are still progressing 5 minutes later.
3. Vasovagal syncope - would give bradycardia, pallor and hypotension, the opposite of this picture.
4. Hypoglycaemia - sweating, confusion, tremor; he is not diaphoretic, the taste is metallic rather than normal, and there is a clear temporal link to the local anaesthetic.
5. Seizure from another cause or hyperventilation - possible, but the sequence of taste → numbness → twitching with a plausible toxic dose makes LAST by far the most likely.

Treat as LAST until proven otherwise; the diagnosis is clinical and waiting for confirmation is dangerous.

Calculation. Articaine 4% = 40 mg/mL. One 1.7 mL cartridge contains 1.7 × 40 = 68 mg. Eight cartridges = 544 mg. The commonly cited maximum for articaine is 7 mg/kg: 70 × 7 = 490 mg. He has therefore received about 54 mg (11%) above the maximum - enough to matter, especially with rapid repeat dosing.

Adrenaline: 1:100,000 = 0.01 mg/mL, so 1.7 mL contains 0.017 mg; eight cartridges = 0.136 mg, which is under the usual 0.2 mg limit for a healthy adult - so the adrenaline is not the primary problem here.

Immediate sequence:

1. Stop the injection and remove the cartridge and needle.
2. Call for help / activate emergency services. Abandon the surgical procedure.
3. Position supine (or semi-recumbent if breathing is compromised); do not let him stand or walk.
4. 100% oxygen by non-rebreathe mask, high flow.
5. Monitor SpO2, ECG, blood pressure and, ideally, capnography; secure IV access.
6. Control seizures/twitching with a benzodiazepine - midazolam 2–5 mg IV titrated, or diazepam 5–10 mg IV.
7. Lipid emulsion 20% - bolus 1.5 mL/kg (about 100 mL) over 1 minute, followed by an infusion of 0.25 mL/kg/min (about 15 mL/min). Repeat the bolus once or twice if the circulation does not improve; continue the infusion for at least 15 minutes after stability. This is the specific antidote and its absence from the kit is a serious gap.
8. Avoid lignocaine, beta-blockers, calcium channel blockers and vasopressin. For hypotension refractory to fluids, use small adrenaline boluses of 10–50 micrograms.
9. Fluids - crystalloid bolus if hypotensive. Begin CPR if arrest occurs, and continue lipid emulsion during resuscitation.

Planning errors, in order of importance:

1. No dose calculation before starting. A simple pre-operative calculation (maximum volume ÷ 1.7 mL) would have flagged that only about seven cartridges were available for a 70 kg patient.
2. Wrong local anaesthetic for the technique. Articaine is well suited to buccal infiltration but offers little advantage for inferior alveolar nerve blocks, where 2% lignocaine with 1:100,000 (max 4.4 mg/kg, about 300 mg or 8.3 cartridges in this patient) or 0.5% bupivacaine provides a better volume-to-toxicity margin. Alternatively, use fewer cartridges of articaine and supplement with a different agent.
3. All four quadrants in one visit. Staging to one side per appointment halves the cumulative dose and shortens the session.
4. Sedation does not reduce the need for local anaesthetic, and the deeper the sedation, the harder it is to detect early warning symptoms such as a metallic taste. If a patient is heavily sedated, the first sign of LAST may be twitching or a seizure.

Practice readiness: the emergency kit must include 20% lipid emulsion for any practice undertaking sedation or high-volume local anaesthesia, together with a printed LAST checklist and an annual team drill. Monitoring should include capnography during sedation, and there should be a written protocol for maximum local anaesthetic dose by weight, displayed in each surgery. Finally, a debrief with the whole team and an incident report are appropriate, and the patient's record must document the event, the doses given and the advice to avoid large volumes of amide anaesthetic in future.