What Causes Loss Of Weight And Appetite Post Aorta Aneurysm Surgery?

My husband had an aorta repair (aorta aneurysm) on jan 7th. 8 hr surgery, on ventillator for 4 days. All doctors say he is doing good; however, he has lost 40 lbs. and there seems to be no answer for him not being able to eat. Says everything has no taste, he is very frustrated. Drinkng Boost as supplement and eating very little. Any help or insight is appreciated. Thank you.