Podcast 818: Local Anesthetics and LAST

Emergency Medical Minute

Contributor: Don Stader, MD

Educational Pearls:

• There are two major groups of local anesthetics: Amide and Esther
• To recall what group an anesthetic belongs to, use this memory trick:

Amide has an ‘i’ in the name and Amide anesthetics have 2 ‘i’s e.g., Lidocaine. Ester has no ‘i’ and most common Ester anesthetics have only one ‘i’ e.g., Tetracaine.

• In a true allergy and/or contraindication to both local anesthetic groups, diphenhydramine is an acceptable alternative.
• Epinephrine is administered with local anesthetics to decrease bleeding, increase duration of action, and minimize systemic spread of the anesthetic, thus reducing toxicity.
• Symptoms of Local Anesthetic Systemic Toxicity (LAST) may begin with dizziness, confusion and/or slurred speech, and can progress to cardiovascular collapse and death.
• Treat LAST with lipid emulsion therapy i.e. ‘Intralipids’ to create a lipid sink that absorbs anesthetic agent
• Administer initial 1.5 ml/kg bolus (approximately 100 ml in 70 mg adult) followed by infusion rate of 0.25 mg/kg/hour. Do not surpass 10 mg/kg total.

References

Dickerson DM, Apfelbaum JL. Local anesthetic systemic toxicity. Aesthet Surg J. 2014;34(7):1111-1119. doi:10.1177/1090820X14543102

Bina B, Hersh EV, Hilario M, Alvarez K, McLaughlin B. True Allergy to Amide Local Anesthetics: A Review and Case Presentation. Anesth Prog. 2018;65(2):119-123. doi:10.2344/anpr-65-03-06

Macfarlane AJR, Gitman M, Bornstein KJ, El-Boghdadly K, Weinberg G. Updates in our understanding of local anaesthetic systemic toxicity: a narrative review. Anaesthesia. 2021;76 Suppl 1:27-39. doi:10.1111/anae.15282

Summarized by Kirsten Hughes, MS4 | Edited by John Spartz MD & Erik Verzemnieks, MD

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