What are the guidelines for calculating local anesthetic doses, such as lidocaine (Lidocaine) and ropivacaine (Ropivacaine), for procedures like brachial plexus block?

Local Anesthetic Dose Calculation Guidelines

For brachial plexus blocks and other peripheral nerve blocks, the maximum safe dose of lidocaine is 4.4 mg/kg without epinephrine and 7.0 mg/kg with epinephrine, while ropivacaine should be dosed at a maximum of 2.0 mg/kg without epinephrine and 3.0 mg/kg with epinephrine. 1

Maximum Dose Calculations for Local Anesthetics

General Principles

• Calculate maximum doses before administration to prevent toxicity
• Use ideal body weight for dose calculations, especially in patients with BMI >30 kg/m²
• For ideal body weight calculation:
  • Men: height in cm - 100
  • Women: height in cm - 105 2

Maximum Recommended Doses

Lidocaine

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

Ropivacaine

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

Specific Dosing for Brachial Plexus Block

Ropivacaine

• Concentration: 0.2% (2 mg/mL)
• Volume: 0.2-0.5 mL/kg
• Maximum volume: 1.5 mL/kg (= 3 mg/kg) 2
• For supraclavicular approach: 10-40 mL (75-300 mg) of 0.75% solution 3
• Onset: 10-25 minutes
• Duration: 6-10 hours 3

Lidocaine

• For brachial plexus blocks: use 1.5 mg/kg as loading dose (infused over 10 minutes)
• Do not exceed 120 mg/hour in any patient 2

Important Safety Considerations

1. Timing with other local anesthetics:

   • Do not start IV lidocaine within 4 hours of any nerve or fascial plane block
   • Do not perform nerve blocks until 4 hours after completion of IV lidocaine infusion 2

2. Patient-specific adjustments:

   • Reduce doses by 30% in infants younger than 6 months 1
   • Do not use IV lidocaine in patients weighing <40 kg 2
   • Use lower doses in very vascular areas to prevent rapid systemic absorption 1

3. Monitoring:

   • Monitor for signs of toxicity: circumoral numbness, facial tingling, slurred speech, metallic taste
   • More severe signs include seizures, CNS depression, and cardiac failure 1
   • Have resuscitation equipment and 20% lipid emulsion available when using higher doses 1

Technique-Specific Dosing

Peripheral Nerve Blocks

• Bupivacaine 0.25%: 0.2-0.5 mL/kg (maximum 2.5 mg/kg) 2, 1
• Ropivacaine 0.2%: 0.2-0.5 mL/kg (maximum 3 mg/kg) 2
• For supraclavicular blocks (which may have higher success rates than axillary blocks): 30 mL (225 mg) of 0.75% ropivacaine 3

Intercostal Blocks

• Bupivacaine 0.25%: 0.1 mL/kg per intercostal space 2, 1
• Ropivacaine 0.2%: 0.1 mL/kg per intercostal space 2

Common Pitfalls to Avoid

1. Calculation errors:

   • Always double-check dose calculations before administration
   • Consider using a nomogram for complex calculations 4

2. Ignoring patient factors:

   • Failure to adjust for age, organ dysfunction, or pregnancy can lead to toxicity
   • Conditions that increase initial uptake (end-stage pregnancy, advanced age) require dose reduction 5

3. Concurrent use of multiple local anesthetics:

   • While mixing long-acting local anesthetics with lidocaine can speed onset, it may affect duration and safety profile 6
   • Account for total local anesthetic load when using combinations

4. Inadequate monitoring:

   • Always monitor patients closely during and after administration of local anesthetics
   • Have lipid emulsion (20%) readily available for treating toxicity 1

Remember that these guidelines provide maximum safe doses, but the actual dose should be the smallest amount required to achieve the desired effect 3.