Dog Collapse and Fainting: What to Do

If your dog collapses, treat it as an emergency, even if he gets back up and seems fine.^1,2 Check that he is breathing and look at his gums: pale or white gums can mean internal bleeding or shock, and blue or purple gums mean low oxygen.^3,4 Start CPR if he isn't breathing and has no heartbeat, cool him if he's overheated, and get to a vet.^3,5,6 The most common causes are heart rhythm problems, internal bleeding (often from a tumor on the spleen), low blood sugar, severe allergic reactions, Addison's disease, heat stroke and, in Labradors and some other breeds, an inherited condition called exercise-induced collapse.^2,7,8,9,10

Fainting, Seizure or Weakness?

Owners often say "collapse" for several different things, and the difference helps your vet find the cause.¹¹ If you can, take a video.

Note what your dog was doing beforehand, how long it lasted, whether he responded to you, any leg movements, drooling or loss of bladder control, his gum color, and how long until he was normal again.¹¹ See seizures in dogs.

Causes of Collapse

• Heart problems are the most common cause of fainting: slow or fast heart rhythms, heart failure, fluid around the heart and narrowed heart valves. Dobermans and Cavalier King Charles Spaniels are at higher risk of heart disease.^2,11 Some medicines that lower blood pressure can also cause fainting.¹¹
• Internal bleeding: a bleeding tumor on the spleen (often hemangiosarcoma) can cause sudden collapse, pale gums and fast breathing in older large dogs, especially German Shepherds, Golden Retrievers and Labradors.⁷ Not every bleeding spleen is cancer: in one study of 60 dogs with sudden internal bleeding, 63% had hemangiosarcoma and 27% had a benign mass.¹⁴ See hemangiosarcoma.
• Low blood sugar: from an insulin overdose in diabetic dogs, xylitol poisoning, an insulin-producing tumor, liver disease, or in tiny puppies and toy breeds. Xylitol signs can start within about 30 minutes.¹⁵ See hypoglycemia and xylitol poisoning.
• Addisonian crisis: dogs can arrive in shock, collapsed and dehydrated, sometimes with an oddly slow heart rate. Standard Poodles, Portuguese Water Dogs and some other breeds are predisposed.⁹ See Addison's disease.
• Anaphylaxis: in dogs, a severe allergic reaction often causes sudden vomiting, diarrhea, weakness and collapse, sometimes without any facial swelling. Insect stings cause about half of cases, followed by vaccines and drugs.^10,16 See vaccine reactions.
• Heat stroke: heavy panting and distress that progresses to collapse. Cool first, then transport.^1,6 See heat stroke.
• Myasthenia gravis: weakness that worsens with activity and improves with rest, often with regurgitation.¹³
• Breathing problems and severe anemia.^11,2 See trouble breathing and pale gums.

Exercise-Induced Collapse in Labradors

Exercise-induced collapse (EIC) is an inherited condition caused by a change in the DNM1 gene. In Labradors, about 30 to 40% are carriers and 3 to 13% are affected. It also occurs in Chesapeake Bay and Curly-Coated Retrievers, several spaniel breeds, Pembroke Welsh Corgis and others.^8,17

• Signs usually start between 5 months and 3 years of age.⁸
• After 5 to 20 minutes of intense, exciting exercise (hunting, repeated retrieves), the dog wobbles, then the back legs give out. Most dogs stay conscious and recover within 5 to 25 minutes.⁸
• Ordinary walks, jogging and swimming rarely trigger it.⁸
• Stop exercise at the first sign of wobbliness, cool your dog and let him rest. A few dogs have died during episodes.⁸
• A DNA test is available. Border Collies can have a similar collapse during herding, but it has a different, still unknown cause.^8,17

What the Vet Will Check

• A detailed history and exam, including heart rhythm, blood pressure and gum color. Your video is very helpful.^11,13
• Bloodwork, including blood sugar, and a urine test.^2,12
• An ECG, chest X-rays and abdominal ultrasound to look for bleeding.^2,18
• A 24-hour (Holter) or longer heart monitor if fainting is suspected, since a short ECG often misses the problem.¹¹
• Specific tests such as a myasthenia blood test or the EIC DNA test.^13,8

Prognosis

• Fainting: dogs recover from the episode itself; the outlook depends on the heart problem. A pacemaker can treat some slow heart rhythms.^2,11
• Bleeding spleen: 63% of dogs with hemangiosarcoma and 88% with a benign mass survived to go home in one study.¹⁴ Long-term survival with hemangiosarcoma is poor; fewer than 10% are alive a year later.⁷
• Addisonian crisis: life-threatening but highly treatable, with an excellent long-term outlook.⁹
• Anaphylaxis: about 85% of dogs survived in reported cases, often after intensive care.¹⁶
• Exercise-induced collapse: most dogs do well once intense training is avoided.⁸

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