Local anesthetic systemic toxicity
- Acronym: LAST
- Life-threatening adverse reaction to local anesthetic toxicity.
- Incidence = ~0.2% of nerve blocks
- Generally occurs within minutes of injection
- Injection of local anesthetic into systemic circulation
- Exceeding the maximum dose of local anesthetic (see table below)
- Absorption of anesthetic into systemic circulation by injection into extremely vascular area.
|Agent||Without Epinephrine||With Epinephrine||Duration||Notes|
|Lidocaine||5 mg/kg (max 300mg)||7 mg/kg (max 500mg)||30-90 min||
|Mepivicaine||7 mg/kg||8 mg/kg|
|Bupivicaine||2.5 mg/kg (max 175mg)||3 mg/kg (max 225mg)||6-8 hr||
|Tetracaine||1 mg/kg||1.5 mg/kg||3hrs (10hrs with epi)|
|Procaine||7 mg/kg||10 mg/kg||30min (90min with epi)|
Diphenhydramine as Local Anesthetic
- Injectable 1% diphenhydramine (10 mg/mL) can be used as a local anesthestic alternative to ester/amide anesthetics
- Sodium channel blocker mechanism
- 1-2 mL of 1% diphenhydramine at a time, to not exceed excessive sedation dose
- Typical vial is 50 mg/mL, so to make 10 mg/mL:
- 10 mL NS removed from 50 mL vial
- Add 10 mL of 50 mg/mL diphenhydramine to 40 mL of NS
- Sedation is dose related and is similar to what would be expected for IM doses
- Relative contraindications are the same for IM diphenhydramine administration
Clinical course tends to be a dose-dependant progression from CNS symptoms to CVS symptoms and death
- CNS symptoms
- Methemoglobinemia - local anesthestics oxidize Fe2+ to Fe3+ in Hb
Sodium Channel Blockade Toxidrome
- Anti-spasmodics, cyclobenzaprine
- Class Ia and Ic antiarrhythmics
- Local anesthetic systemic toxicity
- Venlafaxine toxicity
- Clinical diagnosis
- Directed by clinical picture
- Blood levels of anesthetic are available, but not clinically useful.
- Aggressive supportive care (including airway management) and application of ACLS
- Early activation of ECMO or consideration for transfer to ECMO center as cardiac arrest is often refractory to ACLS.
- 1 amp of sodium bicarbonate IV q2 min for:
- VT or VF
- Severe acidosis
- Lipid emulsion, (Intralipid) 20% solution
- Lipid sink, binds to local anesthetic
- 1.5 mL/kg bolus over 1 minute
- Then, 0.25 mL/kg/min for 20 min or until hemodynamic stability achieved
- ↑ to 0.5 mL/kg/min if hemodynamic status declines
- Maximum total dose 12 mL/kg.
- Consider drawing extra blood as will interfere with labs
- ACLS modifications per ASRA (Am Soc of Regional Anesthesia):
- Avoid vasopressin
- Avoid calcium-channel blockers and beta-blockers
- Amiodarone preferred in ventricular dysrhythmias
- Fencl JL. Local anesthetic systemic toxicity: perioperative implications. AORN J. 2015 Jun;101(6):697-700.
- Sztajnkrycer MD. Local Anesthetics. In: Nelson LS, Howland M, Lewin NA, Smith SW, Goldfrank LR, Hoffman RS. eds. Goldfrank's Toxicologic Emergencies, 11e. McGraw-Hill; Accessed November 29, 2020. https://accessemergencymedicine.mhmedical.com/content.aspx?bookid=2569§ionid=210274249
- Scott DB. "Maximum recommended doses" of local anaesthetic drugs. Br J Anaesth. 1989 Oct;63(4):373-4. doi: 10.1093/bja/63.4.373. PMID: 2818914.
- Pavlidakey PG et al. Diphenhydramine as an Alternative Local Anesthetic Agent. J Clin Aesthet Dermatol. 2009 Oct; 2(10): 37–40.
- Kamel I, Trehan G, Barnette R. Intralipid Therapy for Inadvertent Peripheral Nervous System Blockade Resulting from Local Anesthetic Overdose. Case Reports in Anesthesiology. 2015;2015:486543. doi:10.1155/2015/486543.
- GlobalRPH. Management of Local Anesthetic Emergencies. http://www.globalrph.com/local-anesthetics.htm
- Dillane D, Finucane BT. Local anesthetic systemic toxicity. Can J Anaesth. 2010 Apr;57(4):368-80.