Why do we use glacial acetic acid in lidocaine synthesis?
I think acetic acid is used because it allows you to play funny games with the varying solubility of reactants, products, and by-products. Note that the final product is not soluble in acetic acid/water mixture, but the reactants and salt by-products are. This means that instead of performing an extract in a separatory funnel (extra step, plus you'll need to evaporate solvent and purify), you can just filter the solid product directly from the rest of liquid.

This is the kind of simplifying "magic" you can get when the process chemists get a stab at designing how to run the reaction.