instruction: have the sao2 of patient 021-25408 remained normal on the last intensive care unit visit?
response: SELECT COUNT(*) > 0 FROM vitalperiodic WHERE vitalperiodic.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '021-25408') AND NOT patient.unitdischargetime IS NULL ORDER BY patient.unitadmittime DESC LIMIT 1) AND vitalperiodic.sao2 BETWEEN sao2_lower AND sao2_upper AND NOT vitalperiodic.sao2 IS NULL