instruction: what was the monthly maximum amount of vp shunt drainage given to patient 46764 since 179 months ago?
response: SELECT MAX(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 = 46764)) AND outputevents.itemid IN (SELECT d_items.itemid FROM d_items WHERE d_items.label = 'vp shunt drainage' AND d_items.linksto = 'outputevents') AND DATETIME(outputevents.charttime) >= DATETIME(CURRENT_TIME(), '-179 month') GROUP BY STRFTIME('%y-%m', outputevents.charttime)