[Alkalinization of local anesthetics: theoretically justified but clinically useless]

Abstract

Purpose: In vitro studies have demonstrated the potential advantages of alkalinization on anaesthetic activity, by decreasing the ratio of ionized to nonionized molecules, there by permitting more rapid penetration of local anaesthetic through biological membranes, thus decreasing the onset time. The proportion of each form depends on the pKa of the agent and the ultimate pH of the solution. When NaHCO3 is mixed with local anaesthetics, CO2 is produced. Carbon dioxide has been reported to enhance local anaesthetic action by diffusion trapping of the cationic form in pH gradient combined with a direct depressant action of CO2. The purpose of this study was to examine if clinical studies confirmed the in vitro action of alkalinisation.

Source: The literature pertinent to alkalinization of local anaesthetics published in the major anaesthesia and pharmacology journals of North America and Europe.

Principal findings: While in vitro studies have demonstrated potential advantages for alkalinization on anaesthetic activity, clinical studies have shown that alkalinization of local anaesthetics produces inconsistent results. For bupivacaine and etidocaine, alkalinization of local anaesthetic solution can produce precipitation, thus limiting the feasibility of increasing the pH.

Conclusions: On the basis of this review, routine alkalinization of local anaesthetics is not recommended.