What are the appropriate doses of local anesthetics, including spinal, regional, and local anesthesia?

Appropriate Doses of Local Anesthetics for Spinal, Regional, and Local Anesthesia

The maximum safe doses of local anesthetics must be calculated before administration, with amide local anesthetics having maximum doses of 4.4 mg/kg without epinephrine and 7.0 mg/kg with epinephrine for lidocaine, and 2.5 mg/kg without epinephrine and 3.0 mg/kg with epinephrine for bupivacaine. 1

Local Anesthetic Classification and Maximum Doses

Amide Local Anesthetics

• Lidocaine:

  • With epinephrine: 7.0 mg/kg
  • Without epinephrine: 4.4 mg/kg
  • Duration: 90-200 minutes 1

• Mepivacaine:

  • With epinephrine: 7.0 mg/kg
  • Without epinephrine: 4.4-5.0 mg/kg
  • Duration: 120-240 minutes 1

• Bupivacaine:

  • With epinephrine: 3.0 mg/kg
  • Without epinephrine: 1.3-2.5 mg/kg
  • Duration: 180-600 minutes 1, 2

• Ropivacaine:

  • With epinephrine: 3.0 mg/kg
  • Without epinephrine: 2.0 mg/kg
  • Duration: 180-600 minutes 1

• Articaine:

  • With epinephrine: 7.0 mg/kg
  • Without epinephrine: Not recommended
  • Duration: 60-230 minutes
  • Not recommended for children under 4 years 1

Ester Local Anesthetics

• Procaine:

  • With epinephrine: 10.0 mg/kg
  • Without epinephrine: 6.0-7.0 mg/kg
  • Duration: 60-90 minutes 1

• Chloroprocaine:

  • With epinephrine: 20.0 mg/kg
  • Without epinephrine: 12.0-15.0 mg/kg
  • Duration: 30-60 minutes 1

• Tetracaine:

  • With epinephrine: 1.5 mg/kg
  • Without epinephrine: 1.0 mg/kg
  • Duration: 180-600 minutes 1

Special Considerations for Different Anesthetic Techniques

Spinal Anesthesia

For spinal anesthesia, bupivacaine is commonly used at the following concentrations:

• 0.5% (5 mg/mL): 15-20 mL (75-100 mg) for lumbar epidural administration 3
• 0.75% (7.5 mg/mL): 15-20 mL (113-150 mg) for cesarean section 3

Regional Anesthesia

For regional blocks, dosing depends on the specific block:

1. Brachial Plexus Block:

   • Bupivacaine 0.5%: 35-50 mL (175-250 mg)
   • Ropivacaine 0.5%: 35-50 mL (175-250 mg) 4, 3

2. Femoral Nerve Block/Fascia Iliaca Block:

   • Bupivacaine 0.25%: 0.2-0.5 mL/kg
   • Ropivacaine 0.2%: 0.2-0.5 mL/kg 1

3. Paravertebral Block:

   • Bupivacaine 0.25%: 0.2-0.5 mL/kg
   • Ropivacaine 0.2%: 0.2-0.5 mL/kg 1

4. Intercostal Block:

   • Bupivacaine 0.25%: 0.1 mL/kg per intercostal space
   • Ropivacaine 0.2%: 0.1 mL/kg per intercostal space 1

Local Infiltration

For local infiltration:

• Lidocaine 0.5-1%: 1-40 mL (5-200 mg)
• Bupivacaine 0.25%: 1-40 mL (5-200 mg) 1

Pediatric Considerations

• Doses of amide local anesthetics should be decreased by 30% in infants younger than 6 months 1
• For caudal block in children:
  • Bupivacaine 0.25%: 1.0 mL/kg
  • Ropivacaine 0.2%: 1.0 mL/kg 1

Safety Precautions

1. Calculate maximum dose before administration to prevent toxicity 1

2. Aspiration before injection to minimize risk of intravascular administration 2

3. Monitor for signs of toxicity:

   • Early signs: circumoral numbness, facial tingling, slurred speech, metallic taste
   • Progression: seizures, CNS depression, cardiac failure 1

4. Have resuscitation equipment and lipid emulsion available when using higher doses of local anesthetics 2

5. Treatment of local anesthetic toxicity:

   • Get help and ventilate with 100% oxygen
   • Perform resuscitation as needed
   • Administer 20% lipid emulsion (1.5 mL/kg over 1 minute) for amide local anesthetic toxicity 1

Common Pitfalls and Caveats

1. Lower doses should be used in very vascular areas to prevent rapid systemic absorption 1

2. Adjust doses for patient-specific factors:

   • Reduce doses in elderly patients
   • Reduce doses in patients with renal or hepatic dysfunction
   • Reduce doses in pregnant patients 5

3. Be aware of additive effects when local anesthetics are combined with sedatives or opioids 1

4. Avoid using long-acting local anesthetics for intravenous regional anesthesia 1

5. For incremental dosing (such as in Mohs surgery), a total dose of 500 mg lidocaine delivered over several hours has been shown to be safe 1

By carefully selecting the appropriate local anesthetic agent, concentration, and dose based on the procedure type and patient characteristics, clinicians can provide effective anesthesia while minimizing the risk of toxicity.