EM · Procedural & diagnostic ED skills
Local anaesthesia and topical agents
Also known as Local anaesthesia · Local anaesthetic agents · Topical anaesthesia · EMLA · LAST (local anaesthetic systemic toxicity) · Infiltration anaesthesia
Local anaesthesia and topical agents in the ED — the amide agents (the local formulary maximum (lidocaine plain-vs-adrenaline milligram ceilings are not in the fetched ASRA abstracts); Lin used bupivacaine LIA 2–3 mg/kg max 300 mg; prilocaine, mepivacaine) versus the ester agents (cocaine, amethocaine/tetracaine, benzocaine, procaine), the maximum safe doses, the mechanism (sodium-channel blockade, ionisation, onset, duration), the adrenaline rules and the end-artery contraindication, the local anaesthetic systemic toxicity (LAST — circumoral tingling, tinnitus, agitation, seizure; hypotension, arrhythmia, cardiac arrest from bupivacaine), the treatment (stop injection, airway, lipid emulsion bolus 1.5 mL/kg (Karaoglu); infusion rates not in fetched ASRA abstracts), and the topical agents (EMLA, Ametop, LET gel, ethyl chloride, lidocaine spray, cocaine). ACEM-primary, globally tagged.
Checked against its sources on 2 Sept 2026
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Red flags
- Bupivacaine cardiovascular toxicity is refractory to standard resuscitation — go straight to lipid emulsion with a recommended bolus of 1.5 mL/kg (Karaoglu); infusion mL/kg/min recipes are not in the fetched ASRA abstracts, do not burn time on escalating inotropes
- Never inject local anaesthetic containing adrenaline into an end-artery territory (fingers, toes, nose, ears, penis) — the vasoconstriction causes tissue necrosis
- Calculate and state the maximum safe dose before drawing up — the local formulary maximum (lidocaine plain-vs-adrenaline milligram ceilings are not in the fetched ASRA abstracts); Lin used bupivacaine LIA 2–3 mg/kg max 300 mg; aspirate before every aliquot to avoid intravascular injection
- Prilocaine and benzocaine cause methaemoglobinaemia — suspect it in the cyanosed infant after EMLA or the cyanosed patient with a normal PaO2 and chocolate-brown blood; treat with methylene blue 1 mg/kg IV (Shibuya)
- LAST can present in a delayed pattern after injection — Neal 2018: trend toward delayed presentation with ultrasound, infiltration and continuous infusions — a late seizure or arrest after a block IS LAST until proven otherwise
Meet the patient
A 72-year-old woman with a displaced femoral neck fracture is given an ultrasound-guided fascia iliaca block — 30 mL of 0.5 per cent bupivacaine. The block looked textbook. Ten minutes later she is drowsy, twitching, then seizing, with a blood pressure of 75/40 and a wide QRS.[1]
The block was never the problem — the timing was. A delayed seizure or arrest after a block is LAST until proven otherwise (Neal 2018 delayed-presentation trend), and bupivacaine arrests do not answer to standard ALS. Hold that picture and everything in this topic — the dose ceiling, the aspiration rule, the lipid rescue — falls into place around it.[1]
References8ShowHide
- [1]Neal JM, Neal EJ, Weinberg GL. American Society of Regional Anesthesia and Pain Medicine Local Anesthetic Systemic Toxicity checklist: 2020 version Reg Anesth Pain Med, 2021.PMID 33148630
- [2]Neal JM, Barrington MJ, Fettiplace MR, et al. The Third American Society of Regional Anesthesia and Pain Medicine Practice Advisory on Local Anesthetic Systemic Toxicity: Executive Summary 2017 Reg Anesth Pain Med, 2018.PMID 29356773
- [3]Fettiplace MR, Weinberg G. The Mechanisms Underlying Lipid Resuscitation Therapy Reg Anesth Pain Med, 2018.PMID 29356774
- [4]Neal JM, Bernards CM, Butterworth JF 4th, Di Gregorio G, Drasner K, Hejtmanek MR, Mulroy MF, Rosenquist RW, Weinberg GL. ASRA practice advisory on local anesthetic systemic toxicity Reg Anesth Pain Med, 2010.PMID 20216033
- [5]Karaoglu RO, Toprak Karaoglu A, Kumas Solak S, Sevdi MS, Demirgan S. Awareness and preparedness for local anesthetic systemic toxicity among surgical clinicians: a multi-center cross-sectional survey study BMC Anesthesiol, 2026.PMID 42399827
- [6]Lin HT, Hsieh PH, Liou JT, Chung YT, Tsai YF. The preventive efficacy of lipid emulsion on the occurrence of local anesthetic systemic toxicity in patients receiving local infiltration analgesia for total joint arthroplasty J Orthop Surg Res, 2024.PMID 39468594
- [7]Shibuya M, Hojo T, Hase Y, Kimura Y, Fujisawa T. Methemoglobinemia caused by a low dose of prilocaine during general anesthesia J Dent Anesth Pain Med, 2021.PMID 34395903
- [8]Kim H, Hwang K, Yun SM, Kim DJ. Usage of Epinephrine Mixed With Lidocaine in Plastic Surgery J Craniofac Surg, 2020.PMID 32028367