Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Seamus got into a small amount of sodium hydroxide on Saturday, has been chewing on your metal blinds and had an abrupt change in diet.
In most cases vomiting and loose stools with blood or mucous are triggered by eating something they should not, too much table food, an abrupt change in foods, too many treats or something they find in the home or outdoors.
More serious causes of his symptoms at this age include toxin ingestions, viral or bacterial infections, esophageal reflux, a dietary allergy or sensitivity, inflammatory bowel disease, internal organ failure (kidney or liver disease), or a full or partial gastrointestinal obstruction.
In a young dog, especially if he never finished his vaccine series, a viral infection such as Parvo virus, toxin ingestion, a quick change in food, or a foreign body leading to a partial or full gastrointestinal obstruction would be the most likely causes.
He has had both a quick change in diet and eating irritating foreign material (sodium hydroxide and the blinds) so it is no surprise he's had signs of stomach upset. Sodium hydroxide is a potent gastrointestinal irritant, but I am glad to hear that there were no signs of burns on his lips, tongue or gums. He may have played with it but not ingested enough to cause himself any serious burns. The good news is that he is active and playful, and those point toward this not being too serious, at least at this point.
If he is no longer vomiting then there are some things that we can try at home.
But if he's not improving quickly or he begins vomiting again then he should see a veterinarian for an examination, some diagnostic testing, intravenous fluids and injectable medication to settle his stomach.
To try and settle his stomach today you can give either:
1) Pepcid ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of one half of a 20mg tablet per 20 to 40 pounds of body weight every 24 hours
These are acid reducers and may help settle his stomach and get him feeling better and hopefully stop any vomiting. They should be given for a week or so to help heal any irritation to his gastrointestinal tract.
I would pick up all food for now and water for a couple hours to allow his stomach to settle after the acid reducers.
In a couple hours when you give him water make sure it is in small amounts only. If he drinks too much too quickly that can lead to vomiting. You can also offer ice cubes to lick. To get some electrolytes in you can offer him a 50:50 mix of pedialyte and water.
If there is no vomiting for 5-6 hours offer a bland diet of 1/3 boiled, minced, white skinless chicken or boiled, lean hamburger and 2/3 boiled, white rice mixed with some low salt chicken or beef broth to make it easy to lap up and swallow. I would add in 1-2 tablespoons of canned pumpkin (not pie filling, just pumpkin) to each meal for fiber to cushion any remaining sharp metal blind pieces and help push them through his gastrointestinal tract. If he refuses to eat then don't push it, he needs veterinary care.
But if things go well and he does eat and doesn't vomit feed him the bland diet for 4 to 5 days then slowly start to mix back in his regular food, a little more at each meal. It should take about 5 to 7 days to slowly convert him back to his regular diet.
If he continues to vomit even with the acid reducers, runs a fever (more than 103F rectally), or has a lower then normal temperature (less then 99F), has a tense painful belly, is very lethargic, or if he refuses to eat he should see a veterinarian for an examination, diagnostics, injectable anti-nausea drugs intravenous fluids and supportive care.
Please let me know if you have any further questions.