what is the number of patients who have had a epidural-marcaine intake since 4 years ago?
select count( distinct admissions.subject_id ) from admissions where admissions.hadm_id in ( select icustays.hadm_id from icustays where icustays.icustay_id in ( select inputevents_cv.icustay_id from inputevents_cv where inputevents_cv.itemid in ( select d_items.itemid from d_items where d_items.label = 'epidural-marcaine' and d_items.linksto = 'inputevents_cv' ) and datetime(inputevents_cv.charttime) >= datetime(current_time,'-4 year') ) )