Is adding sodium bicarbonate to hyperbaric bupivacaine for spinal anesthesia recommended?

Adding Sodium Bicarbonate to Hyperbaric Bupivacaine for Spinal Anesthesia

Do not add sodium bicarbonate to hyperbaric bupivacaine for spinal anesthesia, as this causes precipitation of the anesthetic and decreases its efficacy. 1

Why Bicarbonate Should Not Be Added to Bupivacaine

Chemical Incompatibility

• Bupivacaine precipitates when alkalinized with sodium bicarbonate, making the solution unsuitable for clinical use. 1, 2
• Laboratory studies demonstrate that bupivacaine solutions precipitate after adding even small amounts of sodium bicarbonate and cannot be alkalinized to physiologic pH. 2
• This precipitation occurs regardless of whether 4% or 8.4% sodium bicarbonate preparations are used. 2

Contrast with Other Local Anesthetics

• Sodium bicarbonate buffering is highly effective and recommended for lidocaine, where it reduces injection pain by 20-40% and is mixed in a 10:1 or 9:1 ratio. 1
• The American Academy of Dermatology specifically advises against buffering bupivacaine with sodium bicarbonate due to precipitation and decreased efficacy. 1
• Solutions like 2-chloroprocaine and lidocaine readily alkalinize to near physiological pH without precipitation, unlike bupivacaine. 2

Limited Clinical Benefit Even When Technically Possible

Plain Bupivacaine Data

• One older study using plain (non-hyperbaric) bupivacaine with alkalinization showed only modest prolongations: 15 minutes longer regression to T12, 25 minutes to L2, and 15 minutes longer motor block duration. 3
• The authors concluded these modest prolongations had limited clinical importance. 3
• This study used plain bupivacaine, not the hyperbaric formulation typically used for spinal anesthesia. 3

Hyperbaric Bupivacaine Characteristics

Standard Clinical Practice

• Hyperbaric bupivacaine 0.5% is the most widely used local anesthetic for spinal anesthesia for operative delivery in the UK. 4
• The spread of hyperbaric solutions is considered more predictable, producing fewer high blocks compared with isobaric solutions. 4
• Concentration and volume adjustments (rather than pH manipulation) are the appropriate methods for titrating hyperbaric bupivacaine effects. 5

Common Pitfalls to Avoid

• Never attempt to buffer bupivacaine solutions with sodium bicarbonate in clinical practice, as the resulting precipitation renders the solution ineffective and potentially unsafe. 1, 2
• Do not extrapolate the benefits of lidocaine buffering to bupivacaine—these are fundamentally different local anesthetics with distinct chemical properties. 1
• If epinephrine is added to any local anesthetic mixture with bicarbonate, use freshly prepared solutions as epinephrine concentration decreases approximately 25% per week after buffering. 1, 6