what was the time of the last bicarbonate lab test of patient 24118 when they came to the hospital last time?
select labevents.charttime from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'bicarbonate' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 24118 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) order by labevents.charttime desc limit 1