Managing vomiting: Examining the physiology, common causes, and control in dogs (Sponsored by Pfizer Animal Health)
Dr. Michael Leib: Let's start by discussing the physiology of vomiting, including the role and importance of the central and peripheral pathways.
Dr. Albert E. Jergens: Simplistically, we can subdivide the pathophysiology of vomiting by cause:
1. Blood-borne toxins or metabolites that stimulate the chemoreceptor trigger zone
2. Input from the central nervous system
3. Stimuli that trigger responses from the vestibular system
4. Visceral vagal nerves, "which send afferent signals from abdominal parenchyma in response to distention, irritation, or inflammation.
The spectrum of clinical cases I see includes vomiting from dietary causes, pancreatitis, inflammatory bowel disease, and liver disease in dogs and cats. I also see chemoreceptor trigger zone-induced vomiting from drugs, blood-borne toxins, or problems secondary to metabolic disturbances (e.g., uremia or hyperbilirubinemia). In my experience, vestibular-induced causes and central nervous system disturbances that cause vomiting are infrequent. Many causes for acute vomiting are self-limiting and will not require specific therapy.
Dr. David Twedt: A lot of veterinarians associate vomiting with the gastrointestinal tract, but receptors also exist in the peritoneum, kidneys, urinary bladder, and thoracic cavity. Anything in those cavities could cause vomiting.
Leib: With gastrointestinal visceral disease, the duodenum is extremely important. Sometimes the cause of the vomiting may be the duodenum or the rest of the small bowel—not the stomach.
Dr. Kenneth Simpson: One of the more common causes of vomiting, apart from uremia, is the rapid administration of intravenous drugs.
Leib: Does anyone think that with disorders such as gastritis, enteritis, or gallbladder disease, the vomiting center may receive input from both visceral afferent nerves and the chemoreceptor trigger zone?
Jergens: I've performed gastrointestinal endoscopy in a handful of vomiting, uremic animals with gastric erosions or obvious mucosal abnormalities. When uremic toxins stimulate the chemoreceptor trigger zone with concurrent gastric mucosal disruption, both conditions may stimulate vomiting. The same is true for acute pancreatitis where mucosal inflammation and metabolic disturbances may contribute to vomiting episodes. Many common diseases have multiple modalities.
Dr. David Williams: We often don't know if the cause is a gastric, pancreatic, or small intestinal modality. When patients have abnormalities in two or three locations, it's sometimes hard to determine a single cause for the vomiting.
Twedt: Inflammatory bowel disease or Helicobacter gastritis cases are probably just peripheral in nature. But in animals with acute gastroenteritis, they ingest something, are affected locally, and may absorb something that causes problems centrally. It's hard to predict.