Lidocaine hydrocarbonate is not superior to lidocaine hydrochloride in interscalene brachial plexus block

To determine the effect of carbonation of lidocaine, a comparison of 1.0% lidocaine hydrochloride (HCl) and 1.1% lidocaine hydrocarbonate (CO2), both with 1:200,000 epineph-rine, was made in this study of 50 patients receiving interscalene brachial plexus blocks. Sensory block was determined by the response to pinprick in the C2-T2 dermatomes, while motor block was assessed by the development of paresis and paralysis at the shoulder and hand. The percentage of patients developing analgesia (decreased sensation to pinprick) and anesthesia (total absence of sensation to pinprick) at each dermatome level as well as the percentage of patients developing motor block was not significantly different between the two forms of lidocaine. The initial onset of analgesia [lidocaine HCI, 4.0 ± 2.4 (SD) minutes; lidocaine CO2,4.3 ± 3.-8 (SD) minutes] and anesthesia [lidocaine HCl, 10.1 ± 5.7 (SD) minutes; lidocaine CO2, 7.8 ± 4.4 (SD) minutes] did not differ significantly between the two groups. At the individual dermatomes, there was no difference in the onset of analgesia except at one dermatome level, C7, which was near the level of local anesthetic injection. Anesthesia onset in each dermatome as well as the onset of motor block did not differ between the two groups. It is concluded that lidocaine CO2 does not offer any significant clinical advantage over lidocaine HCl in interscalene brachial plexus block.