what was the first value of sodium was for patient 23070 since 08/2103.
select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 23070 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'sodium' ) and strftime('%y-%m',labevents.charttime) >= '2103-08' order by labevents.charttime asc limit 1