How do I dose a 70/30 mixture of 0.5% bupivacaine and 2% lidocaine based on a patient’s weight?

Dosing 70/30 Mixture of 0.5% Bupivacaine and 2% Lidocaine

Calculate the maximum dose based on bupivacaine limits: use 0.7 mL/kg of the 70/30 mixture (70% bupivacaine 0.5% + 30% lidocaine 2%), which delivers 2.45 mg/kg bupivacaine and 4.2 mg/kg lidocaine—both safely under their respective maximum doses. 1, 2

Weight-Based Dosing Algorithm

Step 1: Calculate Maximum Volume Based on Bupivacaine Component

• The bupivacaine component is the limiting factor since its maximum safe dose (2.5 mg/kg without epinephrine, 3.0 mg/kg with epinephrine) is more restrictive than lidocaine (4.4 mg/kg without epinephrine, 7.0 mg/kg with epinephrine). 1
• In a 70/30 mixture, 70% is bupivacaine 0.5% (5 mg/mL) and 30% is lidocaine 2% (20 mg/mL). 3, 4

Step 2: Maximum Volume Calculation

• Without epinephrine: Maximum 0.7 mL/kg of the 70/30 mixture
  • This delivers: 2.45 mg/kg bupivacaine (0.7 mL × 0.7 × 5 mg/mL) and 4.2 mg/kg lidocaine (0.7 mL × 0.3 × 20 mg/mL) 1, 2
• With epinephrine 1:200,000: Maximum 0.84 mL/kg of the 70/30 mixture
  • This delivers: 2.94 mg/kg bupivacaine and 5.04 mg/kg lidocaine 1, 4

Step 3: Practical Examples

• 70 kg adult without epinephrine: Maximum 49 mL of 70/30 mixture (171.5 mg bupivacaine, 294 mg lidocaine) 1, 2
• 70 kg adult with epinephrine: Maximum 59 mL of 70/30 mixture (206 mg bupivacaine, 353 mg lidocaine) 1, 4
• 10 kg child without epinephrine: Maximum 7 mL of 70/30 mixture (24.5 mg bupivacaine, 42 mg lidocaine) 1, 2

Clinical Advantages of the 70/30 Mixture

Onset and Duration Profile

• The 70/30 mixture provides rapid onset from the lidocaine component (within 5 minutes) combined with prolonged duration from the bupivacaine component (110-286 minutes). 3, 5
• Epidural studies demonstrate that lidocaine-bupivacaine mixtures produce onset times similar to lidocaine alone but duration intermediate between pure lidocaine (124 minutes) and pure bupivacaine (286 minutes). 3

Motor Blockade Characteristics

• Equal proportions (50/50) of lidocaine and bupivacaine produce the fastest onset and most profound motor blockade, though the 70/30 mixture will still provide substantial motor block with slightly faster onset than bupivacaine alone. 3

Critical Safety Considerations

Pediatric Dose Adjustments

• In infants younger than 6 months, decrease the calculated dose by 30% due to immature hepatic metabolism of amide local anesthetics. 1
• For a 5 kg infant: Maximum 3.5 mL × 0.7 = 2.45 mL of 70/30 mixture 1, 2

Technique-Specific Precautions

• Aspirate frequently before and during injection to minimize intravascular injection risk, particularly in vascular tissues. 1
• In highly vascular areas, use lower doses within the calculated maximum to reduce systemic absorption. 1, 6
• Monitor vital signs every 5 minutes initially when using high doses or injecting into vascular tissues, then extend to 10-15 minute intervals once stable. 1

Toxicity Prevention

• Never exceed the bupivacaine-based maximum dose regardless of the clinical indication, as bupivacaine carries significant cardiac toxicity risk including cardiovascular collapse. 1, 2
• Have 20% lipid emulsion immediately available when injecting long-acting local anesthetics into vascular tissues for treatment of local anesthetic systemic toxicity. 1

Enhancement Strategies

Adding Epinephrine

• Epinephrine 1:200,000 decreases systemic absorption and extends block duration while allowing a 20% increase in maximum safe dose. 1, 4
• Alkalinization with sodium bicarbonate (2 mL of 8.4% added to 20 mL mixture) produces more rapid onset and denser blockade. 4

Alternative Adjuvants

• Preservative-free clonidine 1-2 mcg/kg extends duration to 4-8 hours without increasing local anesthetic dose, though it requires hemodynamic monitoring for hypotension and bradycardia. 2, 7, 8

Common Pitfalls to Avoid

• Do not calculate doses based on lidocaine limits alone—the bupivacaine component is always the restricting factor in this mixture. 1, 2
• For bilateral blocks, halve the per-side dose to ensure total dose remains under the maximum. 2
• Do not use this mixture for intravenous regional anesthesia—long-acting agents like bupivacaine are contraindicated for this technique. 1
• Avoid excessive doses on mucosal surfaces where rapid systemic uptake can occur, leading to seizures or other toxicity. 1