What is local anesthetic systemic toxicity (LAST)?

LAST occurs when local anesthetic plasma concentrations reach levels that affect the central nervous system and cardiovascular system. Symptoms range from tinnitus and perioral numbness to seizures and cardiac arrest. Intralipid 20% is the recommended rescue therapy.

Why does epinephrine increase the safe dose?

Epinephrine causes vasoconstriction at the injection site, slowing systemic absorption of the local anesthetic. This reduces peak plasma concentration and extends the duration of action, allowing a higher total mg dose before toxic levels are reached.

Is bupivacaine more dangerous than lidocaine?

Yes. Bupivacaine binds cardiac sodium channels with high affinity and slow dissociation, making cardiac toxicity harder to reverse. It has a lower mg/kg ceiling (2–3 mg/kg without epi) than lidocaine (4–5 mg/kg without epi). Levobupivacaine and ropivacaine carry lower cardiac risk.

Should I use these doses for children?

These weight-based ceilings apply broadly, but pediatric pharmacokinetics differ. Neonates and infants have lower protein binding and immature hepatic metabolism, increasing toxicity risk. Always consult current pediatric anesthesia references and adjust downward for very young patients.

Are these doses absolute limits or guidelines?

These are consensus-derived maximum recommended doses for educational reference. Clinical context matters — site vascularity, injection technique, patient comorbidities, and speed of injection all affect toxicity risk. This tool does not replace clinical judgment or institutional protocols.

What concentrations are available for each agent?

Common concentrations: lidocaine 0.5%, 1%, 1.5%, 2%; bupivacaine 0.25%, 0.5%, 0.75%; ropivacaine 0.2%, 0.5%, 0.75%, 1%; mepivacaine 1%, 1.5%, 2%; prilocaine 0.5%, 1%, 2%, 3%. The calculator lets you pick the concentration to convert mg to mL.

Local Anesthetic Toxicity Calculator

Enter patient weight and select a local anesthetic to calculate the maximum recommended dose and equivalent volume.

Patient & Agent Details

Patient Weight

Local Anesthetic Agent

Epinephrine (1:200,000)?

No Yes

Solution Concentration

Enter patient weight and select an agent,
then click Calculate Max Dose.

Max Dose

milligrams

Max Volume

0 mg

Dose Reference —

Setting	Max mg/kg	Max Total (this pt.)

Clinical Notes

Educational reference only. These are consensus-derived maximum doses and do not replace clinical judgment, institutional protocols, or current prescribing guidelines. Site vascularity, injection speed, patient comorbidities, and technique all affect toxicity risk.

Summary

Local Anesthetic Systemic Toxicity (LAST) is a rare but life-threatening complication caused by excessive plasma concentrations of local anesthetic agents. Maximum recommended doses vary by agent, concentration, and whether epinephrine is co-administered. This calculator provides weight-based maximum dose guidance for the most commonly used agents — lidocaine, bupivacaine, ropivacaine, mepivacaine, and prilocaine — as a quick educational reference for clinicians.

How it works

Enter the patient's weight in kilograms (or pounds — the tool converts automatically).
Select the local anesthetic agent from the dropdown.
Indicate whether epinephrine (1:200,000) is co-administered — it raises the safe ceiling for most agents.
Choose the solution concentration (e.g., 0.5%, 1%, 2%) to see the equivalent volume in mL.
The calculator shows the maximum dose in mg and the corresponding volume for your selected concentration.
Review the agent-specific notes for relevant clinical considerations.

Use cases

Pre-procedure dose planning for regional or local anesthesia.
Teaching anesthesia residents and nursing students about LAST prevention.
Quick bedside reference when calculating infiltration volumes.
Comparing safe dose ceilings across different agents.
Estimating dose for pediatric patients by weight.
Reviewing pharmacology limits before a nerve block procedure.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu