Ask a Vet: What Causes a Puppy to Collapse?

A Boxer puppy.
A Boxer puppy. Photography by Shutterstock.

A few weeks ago, a 10-month-old Boxer puppy was playing in his owners’ backyard. One of the owners was engaged in a rambunctious game of fetch with the dog. When the dog returned from the final throw, he vomited, then defecated, and then collapsed. The owner scooped him up and rushed him to my office.

I was in the middle of a discussion with the owner of a cat with a bladder infection when the dog arrived. A technician pulled me from the room to evaluate the new patient.

He was in a bad way. He was barely conscious. His gums, which should be robustly pink, were white. There was vomit in and around his mouth. His heart was barely audible, and his heart rate was just 18 beats per minute — about a quarter of the low end of normal for a Boxer puppy in a veterinary hospital. Bloody diarrhea oozed from his anus. His pulses were not palpable — they were too weak to feel. The dog was in shock.

Boxer puppy by Shutterstock.
Boxer puppy by Shutterstock.

Three possible diagnoses immediately to mind. Boxers are prone to a heart condition called arrhythmogenic right ventricular cardiomyopathy. Affected dogs may collapse spontaneously, and they also are prone to sudden death. However, the condition generally is progressive, and it would not be likely to cause such symptoms in a young individual. It was on the list, but at the bottom.

Dogs who vomit may also collapse if they suffer something called a vagal response. The vagus nerve sends impulses that slow heart rate and other physiological functions. The act of vomiting may, under rare circumstances, stimulate the vagus nerve, leading to collapse. Had the puppy suffered from transient gastrointestinal upset that had caused a vagus response? Possibly, but it was not as likely as my first suspicion: anaphylaxis.

Anaphylactic reactions are manifestations of allergy. When a dog is exposed to something to which he is allergic, the immune system may unleash massive quantities of histamine into the body. Heart rate and blood pressure drop. Histamine has effects on the gastrointestinal tract, so vomiting and diarrhea may occur. The two most common triggers for anaphylaxis are arthropod envenomation (a fancy way of saying bee, wasp, or hornet stings) and vaccines.

The dog had been playing in the yard, and bee season was in full effect. Anaphylaxis was my main consideration.  However, to treat the dog properly, I would need to confirm the diagnosis.

Two technicians worked to place an IV catheter while another administered an intramuscular injection of diphenhydramine (also known as Benadryl — an antihistamine). A fourth attempted to measure blood pressure, but it was too low to read. During my physical exam, I had paid special attention to the dog’s mouth; the vomit had been swept out of the mouth to prevent it from being aspirated (inhaled) into the lungs (although it was likely that aspiration had already occurred, more aspiration would make things worse). I also had searched the mouth for evidence of a bee stinger, which would have essentially confirmed the diagnosis. Dogs frequently get stung in the mouth when they make the mistake of chasing and catching a bee.

Bee by Shutterstock.
Bee by Shutterstock.

While the catheter was being placed, I performed an ultrasound evaluation on the dog. His heart appeared subjectively small, compatible with shock. This was significant — Boxers with cardiomyopathy are expected to have enlarged hearts. I next assessed the dog’s liver, which led to a conclusive diagnosis. The liver contains a structure called the gall bladder. When I evaluated the gall bladder with ultrasound, I noted that there was a ring of fluid around it, creating a halo effect. This so-called gall bladder halo is diagnostic for anaphylaxis.

The technicians placed the IV catheter in the nick of time. The dog’s heart rate was slowing further, and was now down to 12 beats per minute. A bolus of intravenous fluids was started to help support blood pressure. Access to the vein also allowed immediate treatment with epinephrine.

Epinephrine, also known as adrenalin, is the cure for anaphylaxis. A technician raced to the crash cart (a tool box which contains a stock of emergency drugs for rapid access) and drew up the epinephrine. It was administered by slow intravenous injection. Within a minute, heart rate and blood pressure started to come up. Five minutes later, the dog’s gums had a trace of pink and the dog had a dazed, “what just happened to me?” sort of expression. About 30 minutes after that, the dog was a normal puppy again.

While the dog was recovering, a sharp-eyed technician searched his feet and found a bee stinger between the pads of the left front foot. Bee stingers are tiny, so it takes good eyes to find them. The dog had stepped on a bee in the yard, and nearly paid for it with his life. The dog was hospitalized overnight for observation, IV fluids, and gastrointestinal protectants.

The owners were happy that their pet had survived, but they were understandably worried about the future. Bees are everywhere. What should they do if the dog collapsed again? My recommendations were booties and an Epi-Pen.

In general, I do not recommend that dogs wear footwear. Booties may interfere with a dog’s grip and sensation and predispose him to injuries. This dog, however, was an exception to my general rule. The next sting might prove fatal, and booties would help prevent the next sting.

Epi-Pens are devices that contain epinephrine. People who are allergic to bees usually carry them to allow for immediate injections of epinephrine in the event of a sting. It turns out that the pediatric-sized Epi-Pens work for many sizes of dogs. The dog left the hospital the next morning little the worse for wear and with a prescription for a pediatric Epi-Pen.

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