Effects of Commercial (pH ˜ 3.5) and Freshly Prepared (pH ˜ 6.5) Lidocaine‐Adrenaline Solutions on Tissue pH

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Abstract
Differences in the effects of commercially available, sodium bisulfite-containing (pH 3.5-4), and freshly prepared (pH 6.5) lidocaine-adrenaline [epinephrine] solutions on tissue pH and tissue oxygenation were studied experimentally. In rabbits, a 5 .times. 5-cm area under the panniculum was infiltrated with 0.9% NaCl, plain lidocaine, plain adrenaline or 1 of the 2 lidocaine-adrenaline solutions. Tissue pH was measured continuously and intermittently in the infiltrated area with monocrystalline Sb needle electrodes. Infiltration of the tissue with the 4 ml vol of a test solution did not induce any significant tissue injury. Tissue pH was decreased for 30 min following plain lidocaine and for 90 min or more following lidocaine-adrenaline infiltration. With the exception of the 1st few minutes no significant differences in the effects on tissue pH between commercial and freshly prepared lidocaine-adrenaline solutions could be seen. Tissue hypoxia occurred only following infiltration with plain adrenaline. In spite of the low pH and the O2-reducing properties of commercial lidocaine-adrenaline solutions, a rapid buffering occurs in the tissues. The use of commercial lidocaine-adrenaline solution for local infiltration seems as safe as that of freshly prepared lidocaine-adrenaline solutions.