what do you do when you don't know what to say?

i went to visit a boy today. i've taken care of him a lot on the inpatient floor. i wrote the discharge summary when he was going home after his 207 day hospital stay for his bone marrow transplant, complicated by everything you could possibly imagine. he's in our picu right now, on an oscillator, edematous, in multi-system organ failure. he has graft vs host disease from his bone marrow transplant. he's dying. i had no idea what to say.
i stood awkwardly in the doorway for a second, my eyes meeting his mother's. there was still so much hope in her eyes, as well as defiance. it was almost as if she were silently daring me to say something sympathetic, as if that would be confirmation that her son was dying.
so i said nothing.
i walked past him, barely glancing at him but seeing immediately that look...if you've ever seen a dying child, you will know what i mean.
i sat down on the chair by the window next to his mother.
"how are you?" i asked.
she smiled. apparently, i had passed the test.
"i'm doing ok," she said with a shrug. "he looks better than yesterday."