Purr request for my dad

My dad is going into surgery tomorrow morning. I talked to him and my mom
tonight, and as expected, they are both apprehensive and scared. My dad has
practically turned into a skeleton. He can't eat, can't sleep and this has
been going on for a long time. I sent him some of my ambien via mail but he
hasn't told me if he tried any to help him sleep and I'm not asking. It's up
to him if he wants to use it.

My worries are that so many I know (elderly) who go into surgery end up with
staph infections, or the malnutrition leading up to surgery makes them
vulnerable. He passed all of the pre-surgery tests but what does that mean?
Anyway, my mom is very worried and my dad even said he is, and he doesn't
normally disclose that sort of emotion.