How to mount a list of data returned from firebase in Ionic 3?

I have the following code, I would like to filter all records that return through a SearchBar , I can not find a way to filter the data that is returned from the database and display on the screen for the user.

ngOnInit(){
        this.itemsCol = this.afs.collection('items');
        this.items = this.pacientesCol.snapshotChanges()
        .map(actions => {
          return actions.map(a => {
            const data = a.payload.doc.data() as Item;
            const id = a.payload.doc.id;
            return { id, data};
          })
        })

      }