Can 20 mL of 0.5 % bupivacaine and 20 mL of 1 % lidocaine with epinephrine be given to an 80‑kg male with bilateral forearm fracture for an axillary block?

Safety Assessment of Proposed Local Anesthetic Doses for Bilateral Axillary Block

The proposed combination of 20 mL of 0.5% bupivacaine (100 mg) and 20 mL of 1% lidocaine with epinephrine (200 mg) is SAFE and appropriate for an 80-kg male with bilateral forearm fractures requiring axillary block. 1, 2

Dose Calculation and Safety Margins

Bupivacaine Dosing

• Maximum safe dose: 2.5 mg/kg for plain bupivacaine, or up to 3 mg/kg (225 mg total) when combined with epinephrine 1:200,000 1, 3, 4
• Proposed dose: 100 mg (20 mL of 0.5%)
• Patient calculation: For 80 kg patient, maximum = 200 mg (plain) or 240 mg (with epinephrine)
• Safety margin: The proposed 100 mg represents only 50% of the plain maximum and 42% of the epinephrine-enhanced maximum 1

Lidocaine Dosing

• Maximum safe dose: 4.5 mg/kg plain, or up to 7 mg/kg (500 mg total) with epinephrine 2, 5
• Proposed dose: 200 mg (20 mL of 1%)
• Patient calculation: For 80 kg patient, maximum = 360 mg (plain) or 560 mg (with epinephrine)
• Safety margin: The proposed 200 mg represents only 56% of the plain maximum and 36% of the epinephrine-enhanced maximum 2

Evidence Supporting Mixed Local Anesthetic Use

Clinical Efficacy and Safety

• Mixing long-acting local anesthetics (bupivacaine) with intermediate-acting agents (lidocaine) for peripheral nerve blocks is safe and effective, providing faster onset while maintaining adequate duration 6, 7
• A randomized study of 82 patients receiving femoral-sciatic blocks with bupivacaine-lidocaine mixtures (total 40 mL: 100 mg bupivacaine + 400 mg lidocaine with epinephrine) demonstrated no toxicity and faster onset compared to bupivacaine alone 8
• Axillary block studies using 40 mL total volume of mixed local anesthetics (prilocaine-bupivacaine combinations) showed excellent safety profiles with no systemic toxicity 7

Pharmacokinetic Advantages

• When bupivacaine and lidocaine are mixed, plasma concentrations of bupivacaine remain lower and decline faster compared to bupivacaine alone, potentially improving the safety profile 8
• The addition of epinephrine (1:200,000) decreases systemic absorption and prolongs block duration, further enhancing safety 5, 8

Critical Safety Considerations

Avoiding Concurrent Local Anesthetic Administration

• Do not administer additional local anesthetic blocks within 4 hours of this axillary block to avoid cumulative toxicity 6
• If supplementation is needed, wait at least 30 minutes and use no more than half the original dose 9

Monitoring Requirements

• Establish intravenous access before injection 4
• Aspirate before injection to confirm proper needle placement and avoid intravascular injection 4, 2
• Monitor for early signs of CNS toxicity: restlessness, metallic taste, tinnitus, perioral numbness, or confusion 4
• Have lipid emulsion 20% immediately available for treatment of potential local anesthetic systemic toxicity 6

Injection Technique

• Use slow, incremental injection rather than rapid bolus to minimize peak plasma concentrations 2, 5
• The transarterial or ultrasound-guided technique is preferred for axillary blocks to ensure accurate deposition 6

Bilateral Block Considerations

The total volume of 40 mL (20 mL per side) is appropriate for bilateral axillary blocks in this clinical scenario, as each side receives well below maximum safe doses 1, 7. The bilateral nature does not change the safety calculation since the doses are calculated based on total body exposure, not per-block exposure 5.

Duration Expectations

• Sensory block duration: approximately 6-8 hours (mixture provides intermediate duration between lidocaine alone and bupivacaine alone) 8
• Motor block duration: similar to sensory block duration 10, 8
• The mixture provides faster onset (15-20 minutes) compared to bupivacaine alone (25-30 minutes) 8

Common Pitfalls to Avoid

• Never use ester-type local anesthetics (tetracaine, procaine) if the patient has cholinesterase deficiency or is taking cholinesterase inhibitors 6
• Do not buffer bupivacaine with sodium bicarbonate, as precipitation may occur and reduce efficacy 6
• Avoid using this combination for intravenous regional anesthesia (Bier block), as bupivacaine carries high cardiotoxicity risk if accidentally released systemically 3
• Reduce doses by 30% in elderly patients (>65 years) or those with significant cardiac, hepatic, or renal disease 4, 5