What milliliter volume of 1% lidocaine with epinephrine is appropriate for a typical 70‑kg adult and a 20‑kg child for fracture reduction?

Lidocaine with Epinephrine Dosing for Fracture Reduction

For a 70-kg adult undergoing fracture reduction, use up to 49 mL of 1% lidocaine with epinephrine (maximum 7 mg/kg = 490 mg); for a 20-kg child, use up to 9 mL of 1% lidocaine with epinephrine (maximum 4.5 mg/kg = 90 mg).

Adult Dosing (70 kg)

Based on dermatologic surgery guidelines, the maximum safe dose of lidocaine with epinephrine for adults is 7.0 mg/kg in a single treatment 1.

Calculation:

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

This guideline recommendation carries Level III evidence (expert opinion) but represents the most current consensus from the American Academy of Dermatology 1.

Pediatric Dosing (20 kg)

For children, the maximum safe dose is 3.0-4.5 mg/kg of lidocaine with epinephrine 1. Using the upper limit for adequate anesthesia:

Calculation:

• 20 kg × 4.5 mg/kg = 90 mg maximum
• 1% lidocaine = 10 mg/mL
• 90 mg ÷ 10 mg/mL = 9 mL maximum volume

Clinical Context for Fracture Reduction

Research specifically examining forearm fracture reduction in children demonstrates that:

• 1.5 mg/kg (low dose) provides adequate anesthesia for angulated and incompletely displaced fractures (94% success rate) 2
• 3 mg/kg (moderate dose) is more reliable for completely displaced fractures (93% success rate versus 67% with low dose) 2

For the 20-kg child with a displaced fracture requiring manipulation, this translates to:

• Moderate dose: 20 kg × 3 mg/kg = 60 mg = 6 mL of 1% lidocaine
• This remains well below the maximum safe dose of 9 mL

Safety Considerations

Critical safety steps to prevent systemic toxicity 1:

• Use the lowest effective dose
• Aspirate before each injection to avoid intravascular administration
• Use incremental injections
• Continuously monitor the patient for early signs of toxicity (perioral numbness, metallic taste, tinnitus, confusion, seizures)

Important caveats:

• These maximum doses assume normal patient physiology and proper injection technique
• The presence of epinephrine allows higher total lidocaine doses by delaying systemic absorption through vasoconstriction 3, 4
• For regional anesthesia techniques (like hematoma blocks for fractures), absorption rates differ from subcutaneous infiltration, but the same maximum dose guidelines apply 1

The epinephrine concentration typically used is 1:100,000 to 1:200,000, which provides effective vasoconstriction and prolongs anesthetic duration 3, 4.