How much saline is needed to dilute 0.5% bupivacaine?

Dilution of 0.5% Bupivacaine with Saline

The specific volume of saline needed to dilute 0.5% bupivacaine depends entirely on your target concentration and total volume required for the specific clinical procedure.

Understanding the Dilution Calculation

To dilute 0.5% bupivacaine to a lower concentration (such as 0.25%), you need to apply the dilution formula: C1 × V1 = C2 × V2, where:

• C1 = initial concentration (0.5%)
• V1 = initial volume of bupivacaine
• C2 = desired final concentration
• V2 = final total volume

For example, to create 0.25% bupivacaine from 0.5% bupivacaine:

• If you start with 10 mL of 0.5% bupivacaine and want 0.25% concentration, you need to add 10 mL of saline to achieve 20 mL total volume 1
• This 1:1 dilution (equal parts 0.5% bupivacaine and saline) creates 0.25% bupivacaine

Common Clinical Dilution Scenarios

For pediatric regional anesthesia procedures:

• Epidural lumbar blocks typically use 0.25% bupivacaine at 0.5 mL/kg (maximum 15 mL), which requires diluting 0.5% bupivacaine 1:1 with saline 2, 1
• Peripheral nerve blocks use 0.25% bupivacaine at doses up to 2.5 mg/kg (1 mL/kg), again requiring 1:1 dilution from 0.5% stock 1
• Wound infiltration uses 0.25% bupivacaine with maximum safe dose of 2.5 mg/kg 1, 3

For continuous infusions:

• Epidural infusions commonly use 0.2% bupivacaine, which requires mixing 2 parts saline with 3 parts of 0.5% bupivacaine (or 1 part saline with 4 parts of 0.25% bupivacaine) 4
• Continuous epidural infusion rates of 0.1-0.3 mL/kg/h of 0.25% bupivacaine are standard 1

Critical Safety Considerations

Always calculate total dose, not just volume:

• The maximum safe dose of bupivacaine is 2.5 mg/kg regardless of concentration 1, 3
• For a 10 kg patient, this equals 25 mg total, which is 10 mL of 0.25% or 5 mL of 0.5% bupivacaine 1
• Dilution changes volume but not total milligrams administered—you must track both

Common pitfall to avoid:

• Do not assume that diluting allows you to exceed maximum safe dosing—the 2.5 mg/kg limit applies to total bupivacaine administered, regardless of concentration 1, 3
• When diluting for nebulization (as with albuterol), minimum 2-3 mL saline is needed for adequate nebulization, but this principle does not apply to injectable local anesthetics 5

Practical Dilution Guide

To create 0.25% from 0.5% bupivacaine:

• Add equal volume of normal saline (1:1 ratio)
• Example: 10 mL of 0.5% + 10 mL saline = 20 mL of 0.25%

To create 0.2% from 0.5% bupivacaine:

• Add 1.5 times the volume of saline
• Example: 10 mL of 0.5% + 15 mL saline = 25 mL of 0.2%