Effective Management of Vomiting and Nausea in Companion Animals

Introduction
Vomiting is defined as retrograde ejection of food or fluid from stomach or small intestine (duodenum). It is a complex reflex act in dogs and cats, requiring the co-ordination of the gastrointestinal and musculoskeletal systems in conjunction with the central, peripheral and autonomic nervous systems. Vomiting is triggered, by various stimuli, which activate the emetic centre within the reticular formation of the medulla oblongata. Some stimuli activate the so-called ‘humoral pathway’ whereby blood-borne toxins and (which the chemoreceptor trigger zone; CRTZ) located within the area postrema. Activation is induced by various emetogenic substances (e.g. uraemic toxins, apomorphine, cardiac glycosides, and cytotoxic agents). Alternatively, receptors in the abdominal viscera (GI tract, pancreas, liver, urogenital tract, and peritoneum) can activate either vagal or sympathetic neurones leading to vomiting via the so-called ‘neural pathway’. These receptors can be activated by inflammation, irritation, distension and hypertonicity. Finally, motion sickness can cause vomiting, due to impulses originating in the vestibular centre (inner ear), which then travel trough the CRTZ to the vomiting centre.

Approach to management of the vomiting patient
The clinician has two main goals when presented with a vomiting animal: first, to establish the cause of vomiting, and second to stop the vomiting in a safe and effective manner. Early in the course of events, the clinician should determine whether or not the animal has a self-limiting or possible life-threatening problem. The cause is rarely apparent in animals with an acute, self-limiting problem; further, these cases rarely require detailed investigations, and symptomatic therapy is sufficient. In contrast, life-threatening acute vomiting requires both diagnostic evaluations, as well as specific and intense supportive therapy. Finally, cats and dogs with chronic vomiting always require detailed investigations to find the cause of the problem. In such circumstances, an organised approach is required, but anti-emetic therapy can be provided to control the clinical signs whilst the cause is established.  [...]