ABSTRACT: Veterinary nurses in practice play an important role in triaging cases of vomiting, so it is essential for them to have a good understanding of the causes of vomiting, the appropriate advice to give worried owners, the treatment options available, how a diagnosis may be achieved and what prescribed medications help.

Basic anatomy and physiology

Vomiting (emesis) is an active process that must be distinguished from regurgitation (passive) and dysphagia (difficulty swallowing) or retching, coughing and gagging. Identification is achieved by observing the patient eating and for a short time afterwards.

Vomiting is a reflex act initiated by the vomiting centre in the medulla of the brain. This centre stimulates the dorsal vagal complex that causes an initial period of nausea characterised by licking of lips, repeated swallowing, salivation and depression. Vomiting is then achieved by coordinated vigorous contraction of the abdominal, thoracic, diaphragmatic and GI tract muscles, resulting in forceful expulsion of gastric contents from the mouth.

Figure 1 identifies how the vomiting centre can be triggered directly from the cortex, vestibular and sensory vagal and sympathetic stimuli, or indirectly via the chemoreceptor trigger zone (CRTZ).

Figure 1: How the vomiting centre works

The cortex feeds back:

sensory stimuli – such as pain, sight and smell emotional stimuli – such as memory, conditioning, anticipation and fear.

The sensory vagal and sympathetic systems feed back information such as distension, compression, inflammation and drugs or toxins affecting the area. Feedback is achieved from each area via the following neurological pathways:

1.   gastrointestinal (GI) and abdominal area via the vagus and sympathetic nerves

2.   urogenital region via the sympathetic nerves

3.   oral and pharyngeal area via the glossopharyngeal nerve.

The vestibular nerve feeds back from the labyrinth end organs of the ear and vestibular nuclei regarding balance, orientation and co-ordination; this is the area that senses motion sickness. The CRTZ is a collection of receptors located on the floor of the fourth ventricle of the brain, also known as the area postrema, a circumventricular organ lying outside the blood brain barrier (BBB).

The CRTZ is bathed in both blood and CSF located outside the BBB. 

Blood-borne drugs, which either stimulate or inhibit vomiting, can therefore stimulate it. The CRTZ can also detect toxins: hyperammonaemia and uraemia will trigger the vomiting centre.


Vomiting is an important, evolutionary protective mechanism to prevent intoxication or illness through ingestion of spoiled material and also as a way of ejecting indigestible portions of ingesta (especially in omnivores like dogs). Vomiting is not always a sign of illness – it may simply be a reflection of dietary indiscretion and does not always require therapy.

Vomiting is associated with many and varied diseases and as a consequence can cause aspiration pneumonia, oesophagitis, electrolyte acid-base imbalance and dehydration (Table 1).


The nurse must take a thorough history from the owner to determine the severity of vomiting and degree of urgency for the patient to be seen by a veterinary surgeon. Relevant information includes: relationship to feeding frequency duration – acute or chronic (longer than 5 days)

contents – food, bile, liquid, faeces colour – presence of blood or ‘coffee granules’ appearance progression and appetite environmental factors – indoor, outdoor, single or multi-animal household dietary change – intolerance or allergy exposure to toxins, poisonous plants, scavenging or access to foreign bodies drug therapy – accidental or prescribed vaccination history – check infectious disease risk

presence/absence of abdominal pain age, breed, gender and reproductive status weight and body condition, especially if recently changed mentation changes (may indicate dehydration).

Advising owners

In a mildly affected case, where vomiting has been of short duration, the patient is bright and not been in contact with toxins or foreign bodies, owners should withhold food for 24 hours. Once the vomiting stops, they should feed a small amount of bland food (or a recovery diet) at frequent intervals, gradually returning to the normal diet. Fatty food should be avoided as it delays stomach emptying.

We often rely on information provided by the owner over the telephone. If there is any doubt, or if the owner is worried, advise that he or she brings the patient to the practice, so that a physical assessment can be performed.

An appointment is essential if vomiting has continued for longer than 24 hours, if the patient is depressed, lethargic, has concurrent diarrhoea or haematemesis. Retching or non-productive vomiting along with a distended abdomen may indicate that the patient has a gastric dilation volvulus (GDV), which is clearly an emergency situation.

Diagnostic tests

The veterinary surgeon gains most information through the history and physical examination; but a vomiting patient may be admitted for observation and diagnostic tests (such as radiography, ultrasonography, endoscopy, blood analysis) to determine the underlying cause.

First-line treatment

Fluid and electrolyte replacement may be required to correct and maintain hydration and electrolyte balance, until normal fluid and food intake is achieved. Surgery may be required for conditions such as GDV or intussusception; or possibly an exploratory laparotomy to take full thickness biopsies for diagnostic purposes.


Medications that may be prescribed include: GI protectants if there is gastric ulceration, GI pro-kinetics to treat ileus, and anti-emetics to control vomiting. Figure 2 demonstrates where in the cycle four anti-emetic drugs act by targeting individual receptors.

Figure 2: Medication to control vomiting

Metoclopramide* acts on dopamine (D2) receptors, blocking their stimulation on the CRTZ and the vomiting centre. This drug also blocks D2 receptors of the upper GI tract and stimulates muscarinic acetylcholine (M1), having a pro-kinetic effect. In cases that have a suspected foreign body or intussusception, metoclopramide’s pro-kinetic effect may worsen the condition.

Maropitant (Cerenia) inhibits vomiting by acting on NK-1 receptors of the vomiting centre. It is licensed for use in dogs (not cats yet) and used to treat and prevent vomiting caused by chemotherapy and motion sickness.

Ondansetron* (Zofran) blocks serotoninergic 5-
hyroxytryptamine (5-HT3). It acts on the receptors located in the CRTZ and also act at the sensory vagal targeting the GI tract vagus nerve.

It is rarely used in veterinary medicine but is another option.

Prochlorperazine* (Stemetil) and chlorpromazine* (Largactil) have antiemetic effects by blocking dopamine D2, MX and histamine H1 at the CRTZ, vomiting centre and the vestibular area. They are occasionally used to treat motion sickness and vomiting associated with vestibular conditions.

Nursing the patient

The following nursing care should be considered to aid comfort, recovery and diagnosis:

grooming and cleaning (especially if soiled)

oral care (use water to moisten the tongue, gums and lips every 4 – 6 hours, if not drinking) appropriate analgesia for abdominal pain, medications and fluid therapy as prescribed by the veterinary surgeon accurate recording of information describing vomiting, if observed review isolation requirements for infection control especially in diarrhoea or jaundice cases.


Practice protocols are essential to good client communication and patient care in vomiting cases. It is important that a protocol is comprehensible so that when a genuine emergency arises, the veterinary practice team will work efficiently.

These agents are not licensed for veterinary use and their use must be justified under the prescribing cascade system, for example only when a licensed product has not been effective in controlling vomiting.


Anya Owen RVN

Anya Owen works at Dick White Referrals, an expanding private veterinary referral centre that offers specialist care for small animals. She is the senior nurse in the medicine department, with a dedicated team of four qualified nurses who assist the three medical clinicians with all medical, cardiology and oncology patients referred for care. Anya is also studying towards the Diploma of Advanced Veterinary Nursing and is currently in her second year at Myerscough College

Veterinary Nursing Journal • VOL 25 • No5 • May 2010 •