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A dog can have a gastric dilation (bloat) without having a torsion. However a bloat can rapidly become a torsion (volvulus), which is a life threatening emergency. The most obvious signs are what you are describing with the swollen stomach
. Dogs that develop nonproductive vomiting may have a torsion. When there is a torsion the stomach continues to get bigger and eventually breathing becomes difficult and circulation collapses and dogs can rapidly die. Other signs include significant restlessness and intense abdominal pain (may be seen as profuse salivation). If a dog's condition worsen, especially if volvulus has occurred, the dog may go into shock and become pale, have a weak pulse, a rapid heart rate, and eventually collapse.
A dog with gastric dilatation (bloat) without volvulus can show all of these signs, and eventually the bloat can resolve. There is a very great risk that is can rotate without warning. A dog that ha a tendency to bloat, is almost certainly going to eventually rotate. Surgery can be done to correct the torsion if it is caught soon enough. Also a prophylactic surgery can done to prevent torsion in dogs that bloat.
BotXXXXX XXXXXne, If your dog's abdomen is getting larger, if he has pale mucus membranes, is having difficulty breathing, or any of the other symptoms I listed, it is probably better to be safe than sorry and see your vet as soon as possible.
I hope this helps.
I'm available to answer any follow-on questions you might have.