count the number of times that patient 73713 had received a vancomycin laboratory test during this hospital visit.
select count(*) from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'vancomycin' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 73713 and admissions.dischtime is null )