What is the recommended protocol for a field block incision using local anesthetics such as lidocaine (local anesthetic)?

Field Block Incision Protocol Using Local Anesthetics

For field block incisions, use a maximum dose of 7 mg/kg of lidocaine with epinephrine or 4.5 mg/kg of lidocaine without epinephrine in adults, with careful incremental injection technique to minimize the risk of local anesthetic systemic toxicity. 1

Preparation and Dosing

• Calculate the appropriate dose based on patient's weight, using ideal body weight for patients with BMI > 30 kg/m² 1
• For adults, maximum recommended doses are:
  • 4.5 mg/kg of lidocaine without epinephrine 1
  • 7.0 mg/kg of lidocaine with epinephrine 1
• For children, maximum recommended doses are:
  • 1.5-2.0 mg/kg of lidocaine without epinephrine 1
  • 3.0-4.5 mg/kg of lidocaine with epinephrine 1
• Do not exceed 500 mg of lidocaine for multistage procedures performed over several hours 1
• Consider adding epinephrine (2.5-5 μg/mL) to prolong anesthesia and reduce bleeding, unless contraindicated (e.g., end arteries) 2, 3

Technique for Field Block

1. Prepare the skin with antiseptic solution 2
2. Use a small gauge needle (25-30G) for infiltration 4
3. Infiltrate anesthetic around the border of the surgical field, leaving the operative area undisturbed 4, 5
4. Aspirate before each injection to avoid intravascular administration 1
5. Use incremental injections to minimize pain and risk of toxicity 1
6. Allow 5-10 minutes for complete anesthesia to develop before beginning the procedure 4, 6

Safety Considerations

• Use the lowest effective dose of local anesthetic 1
• Aspirate before each injection to avoid intravascular administration 1
• Monitor for signs of local anesthetic systemic toxicity (LAST) including:
  • Early signs: circumoral numbness, facial tingling, slurred speech, metallic taste, tinnitus, light-headedness 1
  • Progressive signs: muscle twitching, seizures, loss of consciousness, respiratory arrest, cardiac arrhythmias, and potentially cardiac arrest 1
• For patients with true lidocaine allergy (rare, approximately 1% of adverse reactions), consider alternatives:
  • Ester-type local anesthetics 1
  • 1% diphenhydramine (longer onset time of 5 minutes vs. 1 minute for lidocaine) 1
  • Bacteriostatic normal saline (0.9% benzyl alcohol in normal saline) 1

Special Considerations

• Do not use intravenous lidocaine within 4 hours of field block anesthesia 1
• Do not perform field blocks until 4 hours after completion of intravenous lidocaine infusion 1
• For pregnant patients, use caution as local anesthetics rapidly cross the placenta 7
• For patients with renal, hepatic, or cardiac disease, consider dose reduction due to altered pharmacokinetics 3
• For multistage procedures like Mohs micrographic surgery, a maximum dose of 500 mg lidocaine delivered over several hours is recommended 1

Advantages of Field Block

• Provides effective anesthesia for procedures including skin biopsy, excision, wound closure, tissue rearrangement, skin grafting, and laser procedures 1
• Can be combined with other anesthetic techniques (topical, nerve block) for larger or more complex procedures 1
• Avoids distortion of the surgical site that can occur with direct infiltration 4, 5