gallblader problems

my husband had gallbladder removed. they put a drain tube in.he was fine after surgery.the next day they removed drain tube an sent him home within three and a half hours he was vomiting a brownish green colored liquid with a very bad smell. returned to hospital  had to have second surgery was told there was a tear at incison site an  bowel was pertruding had to push back in . than was told by the way your husbands gallbladder was gangrene i think something happened when doctor yanked drain tube out .please let me know what could have happened .