Addition of sodium bicarbonate to lidocaine decreases the duration of peripheral nerve block in the rat

Abstract

Background: Adding sodium bicarbonate to lidocaine to enhance its efficacy during peripheral nerve block is controversial. The authors studied the effect of adding sodium bicarbonate to lidocaine with and without epinephrine versus equivalent alkalinization by sodium hydroxide (NaOH) on onset, degree, and duration of peripheral nerve block.

Methods: Part I examined alkalinization by sodium bicarbonate versus NaOH to pH 7.8 on 0.5% lidocaine, with and without epinephrine (1:100,000), prepared from crystalline salt. Part II examined 0.5% and 1.0% commercial lidocaine solutions, with and without epinephrine, either unalkalinized or alkalinized with sodium bicarbonate or NaOH. With NaOH, pH was adjusted to 7.8, but with sodium bicarbonate, no pH adjustments were made to simulate clinical conditions.

Results: In part I, addition of either NaOH or sodium bicarbonate to 0.5% lidocaine without epinephrine produced a faster onset than did unalkalinized lidocaine, without effecting degree or duration of block. In solutions with epinephrine there were no differences in onset, degree, or duration between lidocaine alkalinized with sodium bicarbonate versus NaOH. In part II, addition of sodium bicarbonate or NaOH to 1.0% commercial lidocaine without epinephrine did not accelerate onset compared with the unalkalinized solution. However, adding sodium bicarbonate decreased the degree and duration of block by 25% and more than 50%, respectively, compared with lidocaine unalkalinized and alkalinized with NaOH. With epinephrine, sodium bicarbonate hastened onset without effecting degree and duration compared with the unalkalinized solution.

Conclusions: With 1% commercial lidocaine without epinephrine, sodium bicarbonate decreases the degree and duration of block. However, in solutions with epinephrine, sodium bicarbonate hastens onset, without effecting degree or duration.