What is the effect of adding bicarbonate to a local anesthetic?

Adding bicarbonate to a local anesthetic primarily acts to increase the pH of the solution, making it more alkaline. This change in pH is crucial because local anesthetics are weak bases. In a more alkaline environment, a greater proportion of the anesthetic exists in its non-ionized form, which is more lipid-soluble and can more easily cross neural membranes to exert its effect. As a result, the onset of anesthesia is hastened.

In practical terms, when the pH of the anesthetic solution is closer to physiological pH, the anesthetic can more effectively penetrate nerve membranes, leading to a quicker onset of action. This is particularly important in clinical settings where rapid pain control is needed. Thus, the addition of bicarbonate not only speeds up the onset but enhances the overall efficacy of the anesthetic.