German shepherd vomiting blood and bleeding out anus

I joined to ask about my dog that recently passed away and I was hoping for some good opinions for closure. Thursday my dog was acting completely normal happy as can be untill it was bed time and he started to act like his back paw/leg was hurting. I looked at it and it seemed normal, he was always doing something to make one of his legs hurt and i just thought he was fine. So I went to bed. The next morning i woke up to pools of blood that he vomited all through out the house i found him and saw blood also coming from his anus. Shocked at all the blood I let him out in the back yard to figure out what to do. He was acting like he was going to die laid up under a Bush and wouldn't come to me when I called him. He definitely wasn't feeling good and we took him to the vet. We couldn't go in since the whole covid thing so they just kept my girlfriend updated over the phone and I went to work. He was there for 4 hours and they ran all kinds of tests. The said they didnt need to do a xray because they ruled out a few things. So 4 hours later they was going to give him fluids and some antibiotics but right after they called saying they was finally going to give him fluids he started the death breath. They gave him cpr and I think epinephrine, he came back for a minute just to slip out again. The vet told us he couldn't find a answer why this happened. Now I'm not a vet but I personally feel like giving him fluids should of been the first thing they should of done since he puked so much and lost alot of blood. Our neighbors also hated or dogs. I never mentioned that to the vet but could someone of poisoned our dog? I would also like to know about the vet not giving our dog fluids to begin with, is that normal I dont know enough to say and if anyone has any theory of why it happened I'd really appreciate it. thanks abunch we are all missing our dog very much.

First, here is a huge hug; I am so sorry to read about your dog. That's a horrible thing to happen and so fast, it's no surprise that you have come away with your mind reeling and still with questions pinging into your head.  I would go so far as to say that it is normal to want more confirmation as to what happened; it must have been an emotional time to be taking in large swathes of information.  I am not sure myself what happened to your loved one; it is fairly unusual for V & D patients to present lame and may be a coincidence (the lameness exacerbated by belly-ache or dehydration or even electrolyte changes) .  However, if my experience of losing patients is anything to go by, your vets will probably also have been reviewing the case over and over in their heads, hoping they did did the best they could for your pet and to see if there is anything they can learn. Many vomiting and diarrhoea patients do go straight on to fluids and because I wasn't there, I cannot explain why this didn't happen in this case.  However, your vet should be able to explain what their thinking was and it is absolutely okay to make an appointment and ask them.  It may help to have a list of questions ready - perhaps you could even e-mail it to them in advance. Should my dog have been put on fluids sooner?  Why didn't this happen? And: What are the remaining differentials that this could have been?  Which were they able to rule out? And even: is there anything they felt that they or yourself could have done differently with hindsight? It is important that any external vet who reviews the case does so with a copy of the clinical notes and / or radiographs in their hand, because only then would they be in any position to comment.  If you are still not satisfied, then the people to review the case for you would be the RCVS - information available on their website - whose job this is in an official capacity.  Wishing you decent closure and please do let us know how you get on.