what is the total quantity of output that patient 20898 has had on the current intensive care unit visit?
select sum(outputevents.value) from outputevents where outputevents.icustay_id in ( select icustays.icustay_id from icustays where icustays.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 20898 ) and icustays.outtime is null )