instruction: when did the first time patient 027-188709 had a intracranial/cerebral perfusion pressure monitoring - ventriculostomy performed on the current hospital encounter?
response: SELECT treatment.treatmenttime FROM treatment WHERE treatment.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '027-188709' AND patient.hospitaldischargetime IS NULL)) AND treatment.treatmentname = 'intracranial/cerebral perfusion pressure monitoring - ventriculostomy' ORDER BY treatment.treatmenttime LIMIT 1