when patient 20441 received a microbiologic dialysis fluid test for the last time during the first hospital encounter?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 20441 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and microbiologyevents.spec_type_desc = 'dialysis fluid' order by microbiologyevents.charttime desc limit 1