instruction: was sao2 from patient 22897 less than 98.0 until 21 months ago?
response: SELECT COUNT(*) > 0 FROM chartevents WHERE chartevents.icustay_id IN (SELECT icustays.icustay_id FROM icustays WHERE icustays.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 22897)) AND chartevents.itemid IN (SELECT d_items.itemid FROM d_items WHERE d_items.label = 'sao2' AND d_items.linksto = 'chartevents') AND chartevents.valuenum < 98.0 AND DATETIME(chartevents.charttime) <= DATETIME(CURRENT_TIME(), '-21 month')