Unfortunateley this is a difficult problem,and is caused by necrotic tissue in the mouth.Robins was so bad it permeated the whole flat,and when he was admitted to the hospice it was a major issue.Oral hygeine is essential even though it is painful,and we used and small electric fan with an infusion of laveneder oil under the bed or beside his chair.The hospice used a machine that purified and deodourised the room.
Not much other help i can offer i am afraid.

hope someone else might have some better advice.

liz