how many hours has elapsed since the first time patient 1902 had a tpn intake on the current icu visit?
select 24 * ( strftime('%j',current_time) - strftime('%j',inputevents_cv.charttime) ) from inputevents_cv where inputevents_cv.icustay_id in ( select icustays.icustay_id from icustays where icustays.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 1902 ) and icustays.outtime is null ) and inputevents_cv.itemid in ( select d_items.itemid from d_items where d_items.label = 'tpn' and d_items.linksto = 'inputevents_cv' ) order by inputevents_cv.charttime asc limit 1