Local Anesthetic Dosing Calculator
Determines the maximum safe dose of local anesthetics based on drug concentration and patient body weight.
- This calculator provides guidance for maximum dosing of local anesthetic and should not be used as the primary means of dosing. Always double check and err on the side of caution.
- This calculator is not used for liposomal bupivacaine, which is bupivacaine designed in a slow-release injectable delivery system.
There is ongoing debate about which body weight measure best guides safe local anesthetic dosing.
- Some references use the patient’s actual body weight, which is generally appropriate for patients whose weight falls within a typical range.
- People at either end of the weight spectrum are more vulnerable to dosing errors.
- Professional bodies, such as the American Society of Regional Anesthesia and Pain Medicine (ASRA) and the Society for Obesity and Bariatric Anaesthesia (SOBA), advise dosing based on lean body weight (LBW), particularly for patients with obesity.
- Other resources, such as the British National Formulary (BNF) and the Association of Anaesthetists’ nomogram, use ideal body weight (IBW).
Regardless of the calculation method, clinicians should confirm that the final amount remains below the agent’s published maximum dose and remain vigilant for local anesthetic systemic toxicity.
Note: Previous versions of Goldfrank’s reported an increased maximum allowable dosage due to the vasoconstrictive effects of epinephrine when added to local anesthetics. The most recent version no longer includes this adjustment. While there likely is a higher safe dose when epinephrine is added, we no longer include that estimate on this calculator, and as always, dosages should be double-checked and reviewed using your local pharmacy and policies.
- If the anesthetic dose is above the threshold for toxicity, consider lowering the dosage to the weight-determined range.
- Prepare for adverse events by storing a checklist for management as well as intralipid in a nerve block checklist and having intralipid readily available and easy to access.
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LAST is an uncommon but potentially life-threatening complication of local anesthetic use that may be encountered in the ED, hospital, or surgical center.
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Patients at extremes of age or with organ dysfunction are at higher risk. Inadvertent intra-arterial or intravenous injection, as well as repeated doses and higher doses of local anesthetics are associated with greater risk of developing LAST.
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Using ultrasound guidance, aspirating prior to injection, and utilizing the minimal local anesthetic dose needed are techniques that can reduce the risk of LAST.
Diagnosing LAST:
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Local anesthetic toxicity results from sodium channel blockade, which affects the central nervous system and cardiac system. The CNS is more sensitive to the effects of local anesthetics than the cardiac system and will generally manifest signs/symptoms of toxicity first.
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The presenting symptoms of LAST include perioral numbness, metallic taste, mental status changes or anxiety, visual changes, muscle twitching, and ultimately, seizures, coma, and respiratory depression. Cardiovascular effects include tachycardia, hypertension, ventricular arrhythmias and/or asystole.
Management of LAST (see guidelines: American Society of Regional Anesthesia and Pain Medicine Local Anesthetic Systemic Toxicity checklist: 2020 version):
- Management of LAST requires immediate recognition and a coordinated response, starting with stopping the local anesthetic administration and calling for expert help while initiating a dedicated LAST protocol.
- Prioritize airway management, airway support with 100% oxygen or noninvasive ventilation, and support circulation according to advanced cardiac life support (ACLS) guidelines.
- Avoid calcium channel blockers, beta-blockers, and lidocaine, as they can worsen cardiovascular depression and toxicity.
- Use epinephrine in smaller doses (<1 mcg/kg) for LAST-induced shock.
- Seizures should be promptly controlled with benzodiazepines (e.g., midazolam, lorazepam), avoiding propofol which can exacerbate cardiovascular depression.
- For cardiovascular compromise, including hypotension and life-threatening arrhythmias, 20% lipid emulsion therapy is critical.
- Administer an initial bolus (e.g., 1.5 mL/kg over 1 minute) followed by a continuous infusion (e.g., 0.25 mL/kg/min).
- Repeat boluses can be given after 5 minutes for 2 or more times for persistent hemodynamic instability.
- Vigorous resuscitation should continue until stability is achieved, followed by close monitoring in an intensive care setting.
Multiple variables may influence a patient's risk of developing LAST. This weight based calculator should be used to generate a rough estimate for toxic doses.