Hello, my name is***** and I have over 20 years of experience as a veterinarian. I understand that you are concerned about your pup chewing on and possibly ingesting some of the contents of a cold pack, especially given his history of two bouts of pancreatitis.
These often contain gel that probably contains propylene glycol.
Propylene glycol can be toxic, but enormous quantities would have to be ingested in a bigger dog to see toxic effects. It is much less toxic than the related compound ethylene glycol responsible for antifreeze toxicity. No clinical signs were seen when a dog was given a dose of pure propylene glycol of 10 mls (2 teaspoons) per pound of body weight.
In very large amounts that are toxic quantities we can see acidosis, liver damage, and kidney damage. Clinical signs of a propylene glycol toxicity include central nervous system depression, weakness, incoordination and seizures. In the case of a large ingestion, large quantities of fluids to flush the toxin out, and supportive care, such as treatment for acidosis, should be given.
This substance has a pretty bitter taste so I suspect that he may have bitten the ice pack and played with it but probably didn't truly ingest much.
I wouldn't expect to see any problems at all other than mild stomach upset with the amount in one gel pack in a big dog. You can flush his mouth with cool water to remove any traces of it.
Did he eat any of the plastic cover? If he ate the covering and didn't chew it up it may cause a blockage if he ate enough of it.
If he has a sensitive stomach and you believe he may have swallowed the plastic cover in big chunks you can feed him a bland diet with added fiber. A homemade bland diet consists of 1/3 boiled, lean hamburger (or boiled, white skinless chicken), all fats drained off the meat, mixed with 2/3 boiled, plain white rice. Feed several small meals a day. You might wish to add 1-2 tablespoons of canned pumpkin (not pie filling, just pumpkin) to each meal if you think he did ingest the plastic in big chunks to help increase fiber, which will help push pieces through.
Feed this food for several days and if he is doing well then gradually start mixing in his regular diet, more at each meal. It should take about a week to get him converted back.
Signs that things aren't going well, and he needs an immediate veterinary visit, are vomiting, a tense painful belly, lack of an appetite, a fever (more than 103.5F rectally) and lethargy. This could be related to the plastic pieces getting stuck, or it could be stomach irritation from swallowing some of the gel.
Let me know if you have any further questions.