Buffering capacity of normal and inflamed tissues following the injection of local anaesthetic solutions.

This study has compared the buffering capacity of inflamed skin with that of normal skin, in rats, following the injection of commonly used, relatively acidic local anaesthetic solutions. Inflammation was induced by the intradermal injection of 1% carrageenan 0.1 ml. Local anaesthetic solution (0.05 ml) was injected intradermally into four to six animals in the irritant (inflamed skin) and control (normal skin) groups. Tissue pH changes were measured continuously by a Roche tissue pH electrode for up to a maximum of 180 min. Contrary to the generally accepted view, there was an increase in buffering capacity in inflamed tissues, thus offering no support for the hypothesis that tissue acidity in inflammation is an important factor in the failure of local anaesthetics to act in inflamed tissues.