how much ipratropium bromide neb dose has been prescribed to patient 3229 since 12/2105?
select sum(prescriptions.dose_val_rx) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 3229 ) and prescriptions.drug = 'ipratropium bromide neb' and strftime('%y-%m',prescriptions.startdate) >= '2105-12'