What are earliest signs of local anesthetic systemic toxicity (LAST), and what lipid emulsion regimen is recommended?

• A. Circumoral numbness, tinnitus, metallic taste, perioral tingling; treat with 20% lipid emulsion 1.5 ml/kg IV bolus, followed by 0.25-0.5 ml/kg/min infusion for 10-30 minutes, max dose 10 ml/kg
• B. Facial swelling and hypotension managed with saline
• C. Chest pain and hypertension managed with nitrates
• D. Seizures treated with benzodiazepines

Answer: (A)

Early signs of local anesthetic systemic toxicity are neuro-related, reflecting rising CNS levels before the heart is affected. You’ll typically notice circumoral numbness, perioral tingling, a metallic taste, and tinnitus. These symptoms signal that the local anesthetic is entering the systemic circulation and can progress to seizures or cardiovascular collapse if not treated promptly. The recommended lipid emulsion therapy uses 20% lipid emulsion: give a 1.5 mL/kg IV bolus, then start an infusion of 0.25–0.5 mL/kg/min for 10–30 minutes, with a maximum cumulative dose around 10 mL/kg. The lipid infusion acts as a “lipid sink,” reducing free circulating local anesthetic and providing a fatty-acid energy source to the myocardium, helping stabilize both neurological and cardiovascular status. Other options describe allergic reactions, chest pain with hypertension, or seizure management, which do not capture the earliest signs or the specific lipid-emulsion regimen used for LAST.