Few things are scarier than seeing your dog suddenly collapse. A few quick observations as you head for the veterinarian can help assure your dog gets the proper treatment as quickly as possible. There are multiple causes of collapse and these can vary with the age of your dog.
Problems of the Heart
While dogs do not normally suffer the classic heart attacks we see in people, there are canine heart conditions that may cause an acute collapse. Dilated cardiomyopathy is a disease with an inherited predisposition for some breeds such as Doberman pinschers and boxers. In this case, the heart (“cardio”) muscle (“myo”) is stretched and thinned out so much it can no longer efficiently pump the right amount of blood. The body receives less oxygenated blood than it needs, and areas get shut down, leading to collapse. Some dogs with this problem simply run across the yard and drop dead. If caught early, by noticing less stamina, perhaps labored breathing or on a routine exam by your veterinarian, this condition can be controlled for a while with medications. Unfortunately, the only real cure is a heart transplant, which isn't available for dogs.
Atrial and ventricular fibrillation, in which the small atrial or larger ventricular chambers of the heart beat so fast they don't actually move much blood, can also lead to acute collapse. This can be caused by damage to the heart muscle or the nerves controlling the heart rate or by stimulating toxins. This condition may be diagnosed in a routine exam, or you may notice a lack of energy and stamina in your dog, coupled often with panting or pacing.
Not Enough Oxygen
Along with the heart failing to pump enough oxygenated blood, your dog may actually not be getting enough oxygen into his lungs. Simply choking, such as with a tennis ball stuck in his mouth, blocking his airways, could cause an otherwise healthy dog to collapse. In this case, you must quickly pull that obstruction out.
Dogs with short faces — the brachycephalic breeds, such as English and French bulldogs — may suffer from brachycephalic syndrome, especially in hot, humid weather. These breeds often have small nasal openings and a long soft palate (flap on the roof of the mouth). When a dog breathes, air is pulled in, creating some negative pressure inside the palate. In these dogs, the palate may get sucked down and block off the airways. This could lead to a faint or collapse. If your short-faced dog labors to breathe in hot, humid weather, ask your veterinarian to do a thorough airway exam (possibly under anesthesia). Surgery may be required to help these dogs breathe easily.
Nerves Gone Astray
Neurologic problems may also lead to collapse. A dog with a sudden injury to the discs in the neck or back, or with chronic degeneration of these discs, may collapse and even be paralyzed. In these situations, the protective shock-absorbing disc in between two vertebrae has been squeezed and is putting pressure directly on the spinal cord. Depending on exactly where this happens, your dog may be in great pain, lose control of his hind end, or even lose control of most of his body. Disc disease is seen in long-backed dogs such as dachshunds and Bassets, but also in Great Danes and Doberman pinschers, which have neck disc problems.
Wobbler's is a common name for a disc problem seen in the necks of certain breeds such as Great Danes and Doberman pinschers. In these cases, the vertebrae of the neck are not stable. When they move, they put pressure on the spinal cord. Anti-inflammatory medications may help, along with management techniques, such as using harnesses instead of collars, but some dogs may require surgery.
Less Common Causes of Collapse
Less common causes of collapse in dogs may be cancer, metabolic problems like Addison's disease, or poisonings. Cancers such as hemangiosarcoma create large tumors in the liver and spleen that are delicate and may easily rupture and bleed out into the abdomen. The sudden, severe blood loss can cause collapse, as can blood loss from a bad wound. In Addison's disease, minerals like sodium and potassium get out of sync and lead to heart problems. Addison's is diagnosed with extensive blood work and requires medical therapy.
An easy way to remember whether the adrenal problem Addison's causes is from too much or too little in the way of secretions is that with Addison's disease, you need to “add” steroids and mineralocorticoids.
Some poisons may lead your dog to collapse. Strychnine causes severe seizures and collapse simply by wearing your dog out from the stress of non-stop seizures. If you suspect poisoning, or if your dog is having multiple seizures, seek immediate veterinary attention.
In some areas, such as Florida, certain toads can release toxic substances through their skin. Small dogs may collapse after catching a toad. If you suspect your dog has ingested toad toxins, quickly washing out your dog's mouth will help.
The bottom line? Collapse of your dog should mean an immediate trip to your veterinarian or emergency clinic.