What is the recommended dose of lidocaine (local anesthetic) for a hematoma block?

Hematoma Block Lidocaine Dosing

For hematoma blocks in adults, use 2-2.4 mg/kg of 1% lidocaine without epinephrine, which typically translates to 10-15 mL for an average 70 kg patient, staying well below the maximum safe dose of 4.5 mg/kg (300 mg total). 1, 2

Recommended Dosing Protocol

Standard adult dose:

• 2-2.4 mg/kg of 1% lidocaine (10 mg/mL) without epinephrine 2
• For a 70 kg patient: 140-168 mg (14-17 mL of 1% solution)
• Maximum absolute dose: 300 mg (30 mL of 1% solution) 1

Pediatric dosing (children >3 years):

• 1.5-2.0 mg/kg without epinephrine 3
• For children <6 months: reduce dose by 30% 3

Critical Safety Considerations

Maximum dose limits:

• Without epinephrine: 4.5 mg/kg (maximum 300 mg in adults) 3, 1
• The FDA specifically recommends not exceeding 4.5 mg/kg for infiltration without epinephrine 1

Important pharmacokinetic data:

• Peak plasma levels occur at 20-30 minutes post-injection 2
• Plasma concentrations from hematoma blocks (at 2.2-2.4 mg/kg) range from 100-1,100 ng/mL, well below the toxic threshold of 5,000 ng/mL 2
• Fracture hematomas represent a highly vascular area with rapid systemic absorption 2

Administration Technique

Injection approach:

• Use aseptic technique via dorsal approach to fracture site 2
• Aspirate before injection to avoid intravascular administration 3
• Onset of anesthesia occurs in less than 5 minutes 2

Special Warnings and Precautions

Avoid combination anesthetics in elderly patients:

• A case report documented a generalized tonic-clonic seizure in an elderly patient who received combined lidocaine and bupivacaine for hematoma block, despite both drugs being within therapeutic ranges 4
• Combination anesthetics may lower the seizure threshold, particularly in elderly patients 4

Contraindications to epinephrine:

• Do not use lidocaine with epinephrine for hematoma blocks, as the fracture site is already highly vascular 2
• While epinephrine increases maximum safe doses to 7.0 mg/kg in other settings, it is not standard practice for hematoma blocks 3

Timing considerations:

• Do not perform hematoma blocks within 4 hours of other local anesthetic interventions to prevent cumulative toxicity 5, 3

Monitoring for Toxicity

Early warning signs (plasma levels 5-10 μg/mL):

• Circumoral numbness, facial tingling, metallic taste 3
• Tinnitus, light-headedness, slurred speech 3

Severe toxicity (plasma levels >10 μg/mL):

• Muscle twitching, seizures, loss of consciousness 3
• Respiratory arrest, cardiac arrhythmias 3

Emergency preparedness:

• Have resuscitation equipment and 20% lipid emulsion immediately available 3
• Monitor vital signs closely during and after the procedure 3

Common Pitfalls to Avoid

• Do not exceed 2.4 mg/kg even though the maximum safe dose is 4.5 mg/kg—the lower dose is effective and provides an additional safety margin 2
• Calculate the dose in milligrams before drawing up the solution to avoid volumetric errors (remember: 1% lidocaine = 10 mg/mL) 3
• Do not combine with bupivacaine in elderly patients due to increased seizure risk 4
• Account for rapid systemic absorption from the fracture hematoma when timing subsequent procedures 2