How much local anesthetic is too much

Every cartridge carries you toward two separate ceilings — the anaesthetic one in milligrams per kilogram, and, where the solution contains a vasoconstrictor, the epinephrine one — and which you reach first changes with the drug and with the standard you are working from: with 2% lidocaine on the higher standard the epinephrine ceiling comes first for most adults, on the conservative standard the anaesthetic ceiling does, so long as you carry the 300 mg cap that standard is usually taught with, with a 4% agent the anaesthetic ceiling does up to the top of the adult range, and with a plain solution there is no epinephrine ceiling at all. Two different standards circulate for the same drugs, the manufacturer and FDA labelling on one side and the more conservative pediatric-academy and older-textbook figures on the other, and US dental schools do not teach them consistently; the first honest step is to say which standard you are working from. The conversion only has to be learned once: milligrams per cartridge equals the percent concentration times ten times the cartridge volume, so at 1.8 mL a 2% lidocaine cartridge is 36 mg, 3% mepivacaine is 54 mg and 4% articaine or prilocaine is 72 mg — and at the 1.7 mL that other cartridges and other dose tables use, every one of those totals is about six per cent lower. When you mix agents the limits are fractional and additive — two drugs each at 60% of their own maximum is 120% of a maximum, not two safe doses. The patients where the arithmetic actually bites are small children, small or sarcopenic adults, and anyone on a nonselective beta blocker — where the limit that matters is on neither table, because the interaction creates it.