I can relate. My brother ate a bottle of pills years back, worst part is no one but me believed him, luckily I know my brother like myself and called for help. They lost him and he had to be revived twice then spent a couple of days in a medically induced coma until he was stabilized. Seeing him in that state is literally the most scared I have ever been in my life and it's something I don't often talk about, scarred me deep in my soul no one is or could be as important to me as him.
Good news is that if your brother was trying to drive himself to get help he still has the drive to live. I am sure they will keep him in observation and then he will probably have to go through programs, inpatient at first then outpatient follow up care.
Just be there for him, not just to keep an eye on him though for that too, and not in a guilt trip way, just be there and care and love.
Ifs tough even though your not the one who did it so not only be in a position where you can be the most help to him, but also don't neglect yourself, you need to be healthy if your going to even attempt to help him in his attempts to get healthy.
I don't really know what else to do but tell you I am here, and will talk to people through PM's. I can't really do much more than relate, but as I said I definitely can do that and even with everything being unique in its own way understand in general what it feels like so I can honestly say I understand enough that my ear is not only open but without judgement and know how much it can affect those close to someone who makes an attempt and the trauma it can cause.
Stay healthy and as strong as you can, but no shame in reaching out, strength in numbers and all.