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 for Lidocaine Local Anesthesia

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

Standard Dose Calculations

Adults

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

Pediatric Patients

• Without epinephrine: 4.4-4.5 mg/kg 1, 3
• With epinephrine: 7 mg/kg for medical procedures 1, 3
• Critical adjustment: Reduce all amide local anesthetic doses by 30% in infants under 6 months 1, 3

Special Populations Requiring Dose Reduction

• Elderly patients: Use reduced doses due to altered pharmacokinetics 1
• Highly vascular areas: Reduce doses due to increased systemic absorption 1, 3
• Intravenous regional anesthesia (Bier block): Maximum dose drops dramatically to 3-5 mg/kg 3

How to Calculate Maximum Volume

Follow this three-step formula: 1

1. Calculate maximum dose in mg: Patient weight (kg) × maximum mg/kg dose
2. Convert concentration to mg/mL:
   • 1% lidocaine = 10 mg/mL
   • 0.5% lidocaine = 5 mg/mL
   • 2% lidocaine = 20 mg/mL
3. Calculate maximum volume: Maximum dose (mg) ÷ concentration (mg/mL) = maximum volume (mL)

Example: For a 70 kg adult using 1% lidocaine with epinephrine:

• 70 kg × 7 mg/kg = 490 mg maximum
• 1% = 10 mg/mL
• 490 mg ÷ 10 mg/mL = 49 mL maximum volume 1

Symptoms of Local Anesthetic Systemic Toxicity (LAST)

Early CNS Signs (appear first)

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

Progressive CNS Toxicity

• CNS excitation 1
• Seizures 1
• CNS depression 1

Cardiovascular Toxicity (late, life-threatening)

• Cardiac depression 1
• Arrhythmias 1
• Cardiac arrest and asystole 1

Special Consideration: Methemoglobinemia

• Cyanotic skin discoloration and abnormal blood coloration 2
• May occur immediately or be delayed hours after exposure 2
• Higher risk in infants under 6 months, patients with G6PD deficiency, and those with cardiac/pulmonary compromise 2

Management of Local Anesthetic Toxicity

Immediate Actions

• Stop local anesthetic administration immediately and call for help 1
• Ensure immediate availability of oxygen, resuscitative drugs, and cardiopulmonary equipment 1, 2

Airway Management

• Administer 100% oxygen 1
• Secure the airway if needed 1

Seizure Management

• Administer benzodiazepines or propofol 1

Cardiovascular Support

• Follow standard ACLS protocols 1
• Critical modification: Reduce individual epinephrine doses to <1 μg/kg (not the standard ACLS doses) 1

Lipid Emulsion Therapy

• Indicated for severe cardiovascular toxicity or refractory seizures 1

Methemoglobinemia Management

• Discontinue lidocaine and any oxidizing agents 2
• Supportive care: oxygen therapy, hydration 2
• Severe cases: methylene blue, exchange transfusion, or hyperbaric oxygen 2

Prevention Strategies to Avoid Toxicity

Pre-Procedure Planning

• Calculate the maximum allowable dose in mg before starting the procedure 1, 3
• Use ideal body weight for calculations, not actual body weight (especially in obese patients) 3
• Consider cumulative dosing in prolonged or multistage procedures 1

During Injection Technique

• Aspirate before each injection to avoid intravascular administration 1, 2
• Reposition the needle until no blood return on aspiration 1
• Use incremental injections rather than bolus dosing 3

Monitoring Requirements

• Document vital signs every 5 minutes initially 1
• Once stable, monitor every 10-15 minutes 1
• Continuously assess and communicate with the patient 1

Common Pitfalls and How to Avoid Them

• Using actual body weight instead of ideal body weight in obese patients leads to overdosing 3
• Not accounting for additive effects when multiple local anesthetics are used concurrently 3
• Failing to track cumulative doses in prolonged or multistage procedures 3
• Incorrect concentration conversion: Always remember 1% lidocaine = 10 mg/mL 3
• Enhanced sedative effects occur when maximum doses of local anesthetics are combined with opioids or other sedatives 3
• Using long-acting local anesthetics (bupivacaine, ropivacaine) for intravenous regional anesthesia dramatically increases cardiac toxicity risk 3