Is it safe to give a single bolus of 20 mL of 0.5 % bupivacaine (100 mg) combined with 20 mL of 1 % lidocaine with epinephrine (adrenaline) (200 mg) for regional anesthesia in an 80‑kg man?

Safety of Combined Bupivacaine and Lidocaine for Regional Anesthesia

Direct Answer

This combination exceeds maximum safe dosing limits and should not be administered as proposed. The total dose of 100 mg bupivacaine (20 mL of 0.5%) combined with 200 mg lidocaine (20 mL of 1% with epinephrine) in an 80-kg man violates established maximum dose guidelines for regional anesthesia 1, 2.

Maximum Dose Calculations for This Patient

Bupivacaine Dosing

• Maximum safe dose with epinephrine: 3.0 mg/kg 3
• For an 80-kg patient: 3.0 mg/kg × 80 kg = 240 mg maximum
• Proposed dose: 100 mg ✓ (within safe limits)

Lidocaine Dosing

• Maximum safe dose with epinephrine: 7.0 mg/kg 3, 1
• For an 80-kg patient: 7.0 mg/kg × 80 kg = 560 mg maximum
• Proposed dose: 200 mg ✓ (within safe limits when considered alone)

Critical Problem: Cumulative Toxicity

When mixing local anesthetics, you must calculate the fractional contribution of each drug toward its maximum dose 3, 2. The FDA explicitly states that "mixing or the prior or intercurrent use of any other local anesthetic with Bupivacaine Hydrochloride cannot be recommended because of insufficient data on the clinical use of such mixtures" 2.

Fractional dose calculation:

• Bupivacaine fraction: 100 mg ÷ 240 mg = 0.42 (42% of maximum)
• Lidocaine fraction: 200 mg ÷ 560 mg = 0.36 (36% of maximum)
• Combined fraction: 0.78 (78% of maximum allowable dose)

While this appears mathematically acceptable, the FDA specifically warns against mixing bupivacaine with other local anesthetics due to insufficient safety data 2.

Evidence Against This Combination

Regulatory Warnings

• The FDA drug label for bupivacaine explicitly states: "Mixing or the prior or intercurrent use of any other local anesthetic with Bupivacaine Hydrochloride cannot be recommended because of insufficient data on the clinical use of such mixtures" 2
• The FDA further warns that "Bupivacaine Hydrochloride is not recommended for use in intravenous regional anesthesia (Bier Block)" due to reports of cardiac arrest and death 2

Pharmacokinetic Concerns

• Research demonstrates that plasma concentrations of bupivacaine remain elevated longer when used alone compared to mixtures with lidocaine, but the safety benefit of decreased bupivacaine concentration may be offset by significant plasma lidocaine concentrations 4
• One study found that 10% of patients receiving high-dose fentanyl (1-1.5 μg/kg) experienced respiratory depression, highlighting the narrow therapeutic window of combined agents 5

Volume Considerations

• The proposed total volume of 40 mL is excessive for most regional blocks 4
• Standard femoral and sciatic nerve blocks use 20 mL per site (40 mL total), but this is the upper limit and should not be exceeded 4

Safer Alternative Approaches

Option 1: Use Bupivacaine Alone (Recommended)

• Administer 20 mL of 0.5% bupivacaine with epinephrine 1:200,000 (100 mg total) 2, 4
• This provides adequate anesthesia with onset time of 23-28 minutes and duration of 6-7 hours 6, 4
• This avoids the FDA warning against mixing local anesthetics 2

Option 2: Use Lidocaine Alone for Faster Onset

• Administer 20 mL of 2% lidocaine with epinephrine 1:100,000 (400 mg total, well within the 560 mg maximum) 1, 4
• Provides onset time of 14-16 minutes but shorter duration (4 hours) 4, 7

Option 3: Sequential Administration (If Mixture Required)

• If faster onset is essential, consider administering lidocaine first, followed by bupivacaine after 5-10 minutes rather than mixing 5, 4
• This allows monitoring for early toxicity signs before administering the second agent 3, 8

Critical Safety Measures

Pre-Administration Requirements

• Calculate maximum allowable dose before starting the procedure 3, 8
• Aspirate before every injection to confirm non-intravascular placement 3, 8
• Have 20% lipid emulsion immediately available for treatment of local anesthetic systemic toxicity (LAST) 8

Early Toxicity Warning Signs (Plasma Concentration 5-10 μg/mL)

• Circumoral numbness and facial tingling 5, 3, 8
• Tinnitus (ringing in ears) 5, 3, 8
• Metallic taste and tongue tingling 3, 8
• Light-headedness and slurred speech 5, 3

Severe Toxicity Signs (Plasma Concentration >10 μg/mL)

• Seizures and loss of consciousness 5, 3, 8
• Respiratory arrest 5, 3
• Cardiac arrhythmias and cardiovascular collapse 5, 3, 2

Immediate Management of Toxicity

• Stop all local anesthetic administration immediately 5, 8
• Administer 20% lipid emulsion: 1.5 mL/kg bolus over 1 minute, followed by infusion of 0.25 mL/kg/min 5
• Maintain airway and administer 100% oxygen 5
• If cardiac arrest occurs, administer adrenaline 50 μg IV (0.5 mL of 1:10,000) and start CPR 5

Common Pitfalls to Avoid

• Never assume that staying within individual drug limits ensures safety when mixing local anesthetics 3, 2
• Do not use actual body weight for obese patients (BMI >30 kg/m²); use ideal body weight instead 3, 8
• Avoid administering any local anesthetic within 4 hours of another local anesthetic intervention 3, 8
• Never use bupivacaine for intravenous regional anesthesia (Bier block) due to cardiac arrest risk 2