When a person who has a bad cough is very old or weak and cannot get rid of the sticky mucus or phlegm in his chest,it will help if he drinks a lot of water.Also do the following:
1.First,have him breathe hot water vapors to loosen the mucus.
2.Then have him lie partly on the bed,with his head and chest hanging over the edge.pound him lightly on the back for 10mins,several times a day if necessary .This will help to bring out the mucus.
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From @andy212