I can understand your concern, and applaud you for taking the time to get advice about something that is so traumatizing for your brother. He is truly blessed to have a sister who cares so much for him and his mental wellbeing.
The reality is he will not stop asking, and he has a right to know. Since I do not know the details myself if there is anything that could seriously upset him it may be best to leave it out for the moment. The last thing you want to do is throw him into a depression.
I would first caution you to speak with his doctor. Let him know the issues and ask him his opinion on the matter. The reason why I say this is his doctor knows his condition far better then you or I and therefor it is better to make sure the doctor thinks he can handle the information first.
Once you have the doctors approval you will want to do this at a time that he is more awake and settled. Not after any kind of serious testing or painful examinations such as dressings. Make sure you are prepared to be there with him for a while after you tell him so you can be there to comfort him and give him company at this time.
Then be honest, if there are certain details that are going to really upset him then now is not the time. Leave them out..........now I will caution you that he may be angry later at not hearing the whole story. Though in the end if the whole story may hurt him then you are better off holding off. When the time comes to tell him those little details, set him down and let him know that due to his condition you had decided to hold off telling him certain things. Explain to him that you did not want to hurt him but the fact was you loved him to much to take a chance on his health.
If any of these details could be seen in the news, or other family could spill the facts then it is better to be upfront as it will be easier coming from you then someone else.
Watch him closely during the conversation, if he becomes upset, agitated or looks like he needs a rest then tell him you will talk more about it later.
In the end he will want to know the truth, but you also must be careful of hurting him more.
If you have any questions or want to talk further feel free to click the reply button.