In terms of texts, try to make statements instead of questions so the person doesn’t feel pressure to respond back – you can use your own words or send a daily/weekly quote:
“I’m with you in my mind and heart today.”
“Sending you love.”
“You are not alone. I’m right here.”
“Praying that today is as gentle as possible for you.”
“You can do this.”
And never ever underestimate a classic…
“I love you.” … This one covers all the bases.
For the most part, it is unnecessary to mention why you are sending the text. They know they are going to the hospital, etc., so you don’t have to say “I’m thinking about you while you are at the hospital today.” Just leave that part out so they don’t have to see the word “hospital” a hundred times in texts that day.