Arthrogram on my shoulder about 4 hours ago. how long does the lidocaine last, what to do?

Depends on agent: If you received Lidocaine alone only an hour so I do not think you received that. Lidocaine with Epinephrine would last 2-3 hours you may have received that drug. If they used Marcaine the duration can go as long as 8 -20 hours. Best to ask the doctor in all likelihood it will wear off in the next few hours then supportive medication should be fine look at what was written in your post care plan.

Less than one day: The effects of lidocaine last less than one day, but usually enough for a patient to get one better night's sleep. I usually also use Celestone (betamethasone) for longer relief of inflammation. I advise my patients not to have physical therapy, strenuous activity or exercise on the day of an arthrogram. Patients can go back to their regular activity the next day.