What are the maximum doses, symptoms of toxicity, and management for lidocaine (local anesthetic) with and without epinephrine (adrenergic receptor agonist) for local anesthesia?

Maximum Dosing and Toxicity Management for Lidocaine with and without Epinephrine

Maximum Dose Calculations

For local infiltrative anesthesia in adults, administer no more than 4.5 mg/kg of lidocaine without epinephrine (maximum 300 mg) or 7 mg/kg with epinephrine, calculating the maximum allowable dose in milligrams before starting any procedure. 1, 2, 3

Standard Adult Dosing

• Lidocaine WITHOUT epinephrine: 4.5 mg/kg (maximum 300 mg total) 1, 2, 3
• Lidocaine WITH epinephrine: 7 mg/kg 1, 2
• The addition of epinephrine allows 55% higher doses due to decreased systemic absorption through vasoconstriction 2

Pediatric Dosing (Critical Differences)

• WITHOUT epinephrine: 4.4 mg/kg 1
• WITH epinephrine: 7 mg/kg (medical procedures) or 4.4 mg/kg (dental procedures) 1
• Infants <6 months: Reduce all amide local anesthetic doses by 30% 1, 2

Special Route Considerations

• Intravenous regional anesthesia (Bier block): Maximum dose drops dramatically to 3-5 mg/kg 1, 2
• Transtracheal/bronchoscopy: Maximum 3 mg/kg (200 mg for 70 kg patient) 3
• Topical spray for laryngoscopy: 0.6-3 mg/kg (40-200 mg) 3

Dose Calculation Formula

To calculate the maximum volume of lidocaine solution you can safely administer:

1. Determine maximum dose in mg: Patient weight (kg) × maximum mg/kg dose
2. Convert concentration to mg/mL: 1% lidocaine = 10 mg/mL, 2% lidocaine = 20 mg/mL 2
3. Calculate maximum volume: Maximum dose (mg) ÷ concentration (mg/mL) = maximum mL

Example for 70 kg adult using 1% lidocaine with epinephrine:

• Maximum dose: 70 kg × 7 mg/kg = 490 mg
• 1% lidocaine = 10 mg/mL
• Maximum volume: 490 mg ÷ 10 mg/mL = 49 mL

Critical Dosing Adjustments

When to Use Lower Doses

• Highly vascular areas: Reduce dose due to increased systemic absorption 1, 2
• Elderly patients: Reduce dose due to altered pharmacokinetics 2, 4
• Hepatic or cardiac impairment: Reduce dose for repeated or continuous administration 4
• Pregnancy (especially end-stage): Reduce dose due to increased uptake rate 4

Epinephrine Concentration

• Use 2.5-5 μg/mL (1:200,000 to 1:100,000) when administering large doses 2, 4
• Both 1:100,000 and 1:200,000 concentrations are equally effective and safe 5, 6

Symptoms of Local Anesthetic Systemic Toxicity (LAST)

Early Central Nervous System Signs (Most Common)

• Circumoral numbness and facial tingling 2
• Metallic taste 2
• Tinnitus and auditory disturbances 1
• Lightheadedness and dizziness 1

Progressive CNS Toxicity

• CNS excitation: Agitation, confusion, muscle twitching 1
• Seizures (generalized tonic-clonic) 1, 2
• CNS depression: Drowsiness, loss of consciousness 1

Cardiovascular Toxicity (More Severe, Later Manifestation)

• Cardiac depression: Hypotension, bradycardia 1
• Arrhythmias: Ventricular tachycardia, ventricular fibrillation 1
• Cardiac arrest and asystole 1, 3

Methemoglobinemia (Rare but Important)

• Cyanotic skin discoloration despite adequate oxygenation 3
• Abnormal blood coloration (chocolate-brown blood) 3
• Symptoms may occur immediately or be delayed hours after exposure 3

Management of Local Anesthetic Toxicity

Immediate Actions for LAST

Stop administering local anesthetic immediately and call for help, ensuring immediate availability of oxygen, resuscitative drugs, and cardiopulmonary equipment. 3

1. Airway management:

   • Administer 100% oxygen 3
   • Secure airway if needed, avoid hyperventilation 3
   • Prevent/treat acidosis (acidosis worsens toxicity) 3

2. Seizure management:

   • Administer benzodiazepines (midazolam or diazepam) 1
   • Small doses of propofol if benzodiazepines unavailable 1

3. Cardiovascular support:

   • Standard ACLS protocols initially 1
   • Reduce individual epinephrine doses to <1 μg/kg 1

4. Lipid emulsion therapy (20% intralipid):

   • Indicated for severe cardiovascular toxicity or refractory seizures 1
   • Should be immediately available when injecting long-acting agents (bupivacaine, ropivacaine) into vascular tissues 1

Management of Methemoglobinemia

1. Discontinue lidocaine and any oxidizing agents 3
2. Supportive care: Oxygen therapy, hydration 3
3. Methylene blue: For severe cases with significant symptoms 3
4. Exchange transfusion or hyperbaric oxygen: For refractory cases 3

Prevention Strategies (Critical to Avoid Toxicity)

Before Administration

• Calculate maximum allowable dose in mg before starting the procedure 1, 2
• Use ideal body weight for calculations, not actual body weight (especially in obese patients) 2
• Consider cumulative dosing in prolonged or multistage procedures 2

During Administration

• Aspirate before each injection to avoid intravascular administration 1, 2, 3
• Reposition needle until no blood return on aspiration 3
• Use incremental injections rather than bolus dosing 2
• Inject slowly to allow time to recognize early toxicity symptoms 2

Monitoring Requirements

• When using high doses: Document vital signs every 5 minutes initially, then every 10-15 minutes once stable 1, 2
• Continuously assess and communicate with the patient 2
• Watch for early warning signs (circumoral numbness, metallic taste, tinnitus) 2

Common Pitfalls and How to Avoid Them

Calculation Errors

• Pitfall: Confusing concentration percentages with mg/mL 2
• Solution: Remember 1% = 10 mg/mL, 2% = 20 mg/mL 2

Cumulative Dosing

• Pitfall: Not tracking total dose in prolonged procedures 2
• Solution: Document each dose administered and maintain running total 2

Multiple Local Anesthetics

• Pitfall: Using multiple local anesthetics without accounting for additive effects 2
• Solution: Calculate total dose of all local anesthetics combined 2

Drug Interactions

• Pitfall: Enhanced sedation when combining maximum doses with opioids or sedatives 1, 2
• Solution: Reduce local anesthetic dose when using concomitant sedatives 1

Timing of Epinephrine Effect

• Pitfall: Making incisions before vasoconstriction takes effect 6
• Solution: Wait 10 minutes after injection in forearm, 8 minutes in face for maximal vasoconstriction 6

Absence of Blood on Aspiration

• Pitfall: Assuming no intravascular injection if no blood returns 3
• Solution: Absence of blood does not guarantee avoidance of intravascular injection; use incremental dosing and monitor continuously 3