For a 70‑kg adult undergoing bilateral forearm surgery, what total volume and mixture of 0.5% bupivacaine and 1% lidocaine with epinephrine (1:200 000) should be used for a single‑shot axillary block per side?

Bilateral Axillary Block for Forearm Surgery: Dosing Recommendations

For a 70-kg adult undergoing bilateral forearm surgery, use 30 mL per side of a 1:1 mixture of 0.5% bupivacaine with epinephrine (1:200,000) and 1% lidocaine with epinephrine (1:200,000), for a total volume of 60 mL across both blocks.

Rationale for Volume and Concentration

Per-Side Volume

• The standard volume for axillary block is 30 mL per side, as demonstrated in a randomized trial using exactly this volume (30 mL of equal parts 0.5% bupivacaine with adrenaline 1:200,000 and 2% lignocaine) for forearm and hand surgery 1
• For ultrasound-guided technique, the minimum effective volume in 90% of patients (MEV90) for perivascular injection is 23.5 mL, with an additional 5.5 mL needed for musculocutaneous nerve block, totaling approximately 29 mL 2
• A study using 20 mL total volume (equal parts 2% lidocaine with 1:200,000 epinephrine and 0.5% bupivacaine) achieved 100% success for upper limb trauma surgery, though this represents a lower volume approach 3

Mixture Composition

• Mix equal volumes of 0.5% bupivacaine with epinephrine (1:200,000) and 1% lidocaine with epinephrine (1:200,000) 1
• Evidence suggests mixing local anesthetics is safe and effective, though no strong evidence proves superiority over single agents 4
• The combination theoretically provides rapid onset from lidocaine and prolonged duration from bupivacaine, though clinical benefit is narrow 5

Safety Considerations for Bilateral Blocks

Maximum Dose Calculations

• Total bupivacaine dose: 60 mL of 1:1 mixture = 30 mL of 0.5% bupivacaine = 150 mg (2.1 mg/kg for 70-kg patient)
• Total lidocaine dose: 30 mL of 1% lidocaine = 300 mg (4.3 mg/kg for 70-kg patient)
• These doses remain well below toxic thresholds with epinephrine present 4
• Bupivacaine is more potently toxic than other local anesthetics, with complications including hypotension, arrhythmias, and cardiac arrest 6

Bilateral Block Considerations

• For bilateral procedures, ultrasound guidance is superior to neurostimulation, with shorter performance time (8.2 vs 14.6 minutes), faster onset of sensory block (14.2 vs 19.9 minutes), and higher patient satisfaction (95.0% vs 83.3%) 7
• Peak plasma concentrations occur approximately 50 minutes after performance 7
• Monitor for systemic toxicity signs throughout the procedure given the cumulative dose from bilateral blocks 7

Technical Approach

Injection Technique

• Use a double-injection technique: one injection for the musculocutaneous nerve (5-6 mL) and one perivascular injection targeting the median, ulnar, and radial nerves (24 mL) 2
• Alternatively, use an orthogonal two-needle technique with needles positioned above and below the axillary artery, aimed toward the posterior fascial compartment containing the radial nerve 1
• The orthogonal approach provides more reliable blockade of all terminal branches including the musculocutaneous nerve distribution 1

Ultrasound Guidance

• Ultrasound guidance is strongly recommended for bilateral blocks due to improved safety profile, faster onset, and higher success rates 7
• Use a needle-out-of-plane approach, identifying each nerve individually before injection 3

Expected Outcomes

Onset and Duration

• Sensory block onset: 14-19 minutes 7
• Motor block onset: 24-29 minutes 7
• Duration of effect: 6-7 hours 5
• No significant difference in onset time between lidocaine alone, bupivacaine alone, or their mixture 5

Clinical Benefits

• Superior postoperative analgesia compared to general anesthesia, with minimal pain scores in recovery (VAS 0.3 vs 55.8) 3
• Ability to bypass recovery room 3
• Earlier achievement of hospital discharge criteria (30 minutes vs 120 minutes) 3

Critical Pitfalls to Avoid

• Do not buffer bupivacaine with sodium bicarbonate, as precipitation may lead to decreased efficacy 4
• Avoid exceeding 30 mL per side to prevent systemic toxicity, particularly with bilateral blocks 7, 1
• Do not use 2% lidocaine concentration as in some cited studies; stick with 1% to maintain safe total dosing for bilateral blocks 1
• Ensure adequate monitoring for at least 50 minutes post-injection when peak plasma levels occur 7