A Practical Guide to Local Anesthetic Options for Wide-awake Hand Surgery (WALANT): A Laboratory-based Experimental Study

Ongoing supply chain issues are impacting local anesthetic availability, limiting choices for hand surgery under local anesthesia (wide-awake local anesthesia no tourniquet [WALANT] hand surgery). WALANT can be safely performed using multiple local anesthesia preparations; however, epinephrine (for hemostasis) and sodium bicarbonate (NaHCO₃) (to reduce injection pain) are often added to create the desired preparation. Here, we tested how much NaHCO₃ to add to various local anesthetic to approximate body pH. Five samples of each commercially available local anesthetics were tested for pH including 1% lidocaine, 2% lidocaine, 1% lidocaine with 1/200,000 epinephrine, 0.25% bupivacaine, 0.5% bupivacaine, 0.5% bupivacaine with 1/100,000 epinephrine, 1% mepivacaine, 2% mepivacaine, and ropivacaine, with or without premixed or exogenous epinephrine. Each sample was buffered with NaHCO₃, with volumes increasing by 0.1 mL until target pH was measured or visible precipitate occurred; 1.0 mL of 8.4% bicarbonate can be added to 10 mL of 1% lidocaine with 1/100,000 exogenous epinephrine to yield pH 7.3. Similarly, with 10 mL 1% lidocaine with premixed 1/200,000 epinephrine, the ideal volume of buffer remains 1.0 mL. Buffering bupivacaine created a solid precipitate in all samples when more than 0.2 mL of NaHCO₃ per 10 mL of sample was added. Ropivacaine precipitated with all volumes of buffer. Mepivacaine can be buffered using 0.3 mL NaHCO₃ per 10 mL to achieve physiological pH, without precipitate. In conclusion, we present guidance for surgeons to mix local anesthetic, epinephrine, and NaHCO₃ to optimize pH for comfortable injection of local anesthesia in WALANT procedures.