instruction: when was last time the sao2 of patient 027-132801 was greater than 99.0 on this month/04?
response: SELECT vitalperiodic.observationtime FROM vitalperiodic WHERE vitalperiodic.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '027-132801')) AND vitalperiodic.sao2 > 99.0 AND NOT vitalperiodic.sao2 IS NULL AND DATETIME(vitalperiodic.observationtime, 'start of month') = DATETIME(CURRENT_TIME(), 'start of month', '-0 month') AND STRFTIME('%d', vitalperiodic.observationtime) = '04' ORDER BY vitalperiodic.observationtime DESC LIMIT 1