dehydration? heat stroke?

Question
we lost our 13 yr old lab/chow mix dog 2 days ago. he had just been to the vet for a check up and vaccinations 2 wks prior and got a clean bill of health. we'd been keeping an eye on both of our dogs (the other has an autoimmune disease) since temperatures in AZ have exceeded 110 degrees this past week. they had plenty of shade and a large bowl of fresh water everyday. the evening before he past away we noticed he was lethargic and wouldn't eat. we let him rest and i assisted him with drinking some water. the next morning he still appeared tired, but was alert and wagging his tail. we decided this time around to leave the dog door open so they could go in and out of the house. unfortunately when we came home that evening we found him dead beneath a bush. after further inspecting the house and yard, i found one small spot of clear vomit inside the house. we're not sure what all these symptoms lead up to and at this point i'm not sure if it was dehydration or heatstroke since he didn't feel hot, his eyes were clear, he was responsive to everyone around him and he wasn't panting. i feel guilty since i feel i could have done something different, but i don't know what i should have looked for or what i could have done differently. please help us understand what may have happened. we're heartbroken.

Answer
I am so sorry to hear about your dog.

Unfortunately, the only way to really know what happened to your guy would have been to do a necropsy.

With those temps, the easy guess would have been heat stroke, but since he was recently vaccinated, I think it could have been a reaction to his inoculations. We are finding that over-vaccinating creates myriads of problems, and the AVMA now recommends vaccines no more often than every three years. I myself never vaccinate old dogs anymore, and, in fact, except for the required rabies, I no longer vaccinate beyond the puppy vacs and the one-year boosters.
http://www.doglogic.com/vaccineinfo.htm#news

http://www.newvaccinationprotocols.com/Adverse%20K9%20Reaction.htm

Karen