Recommended Dose of 1% Lidocaine for Hematoma Block at the Wrist
For a hematoma block at the wrist in adults, administer 2-2.4 mg/kg of 1% lidocaine without epinephrine, which typically translates to approximately 10-15 mL for an average 70 kg adult, staying well below the maximum safe dose of 4.5 mg/kg (300 mg total). 1
Dosing Algorithm
Standard Adult Dosing
- Calculate dose based on body weight: 2-2.4 mg/kg of 1% lidocaine 1
- For a 70 kg adult: This equals 140-168 mg of lidocaine
- Volume conversion: Since 1% lidocaine = 10 mg/mL 2, this translates to 14-17 mL
- Practical range: Most hematoma blocks at the wrist use 10-15 mL of 1% lidocaine 1
Maximum Safety Limits
- Without epinephrine: Do not exceed 4.5 mg/kg or 300 mg total 2, 3
- With epinephrine (if used): Maximum increases to 7.0 mg/kg or 500 mg total 2
- For a 70 kg adult: Maximum of 315 mg (31.5 mL) without epinephrine, but practical doses are much lower 2
Clinical Considerations
Onset and Efficacy
- Onset time: Anesthesia typically begins in less than 5 minutes 1
- Duration: Expect 60-90 minutes of anesthesia with plain lidocaine 1
- Pain reduction: Reduces manipulation pain to modest levels even with lower doses 1
Safety Profile for Hematoma Blocks
- Systemic absorption: Lidocaine is rapidly absorbed from fracture hematomas, with peak plasma levels at 20-30 minutes 1
- Plasma concentrations: At doses of 2.2-2.4 mg/kg, plasma levels range from 100-1,100 ng/mL, well below the toxic threshold of 5,000 ng/mL 1
- Critical warning: Even therapeutic doses can rarely cause seizures, particularly in elderly patients or when combined with other local anesthetics 4
Important Safety Precautions
Avoiding Cumulative Toxicity
- Do not administer lidocaine within 4 hours of any other local anesthetic intervention 2, 5
- Count all routes: Include any topical, infiltrative, or regional anesthetic doses toward the maximum safe total 2
- Remove lidocaine patches before performing the hematoma block 5
Monitoring for Toxicity
- Early warning signs (appear first): Circumoral numbness, facial tingling, tinnitus, metallic taste, slurred speech 2, 6
- Progressive toxicity (requires emergency care): Muscle twitching, loss of consciousness, seizures, respiratory arrest, cardiac arrhythmias 2, 4
- If toxicity occurs: Immediately stop administration, provide airway support, manage seizures with benzodiazepines, and use lipid emulsion therapy for cardiovascular collapse 2, 6
Common Pitfalls to Avoid
- Overdosing in smaller patients: Always calculate based on actual body weight, not a standard volume 3
- Combining anesthetics: The case report of seizure with combined lidocaine and bupivacaine suggests that mixing agents may lower the threshold for complications, especially in elderly patients 4
- Inadequate preparation: Have emergency equipment readily available, including benzodiazepines and lipid emulsion 2
- Ignoring recent anesthetic use: Always ask about recent dental work, topical anesthetics, or patches 2, 5