7. Nausea and Vomiting / M.C. Champion  

Barf, upchuck, bring up. 

Nausea is a psychic as well as physical experience and defies precise definition. Vomiting is evacuation of the stomach contents through the mouth. Nausea normally precedes vomiting. There can be associated tachycardia, hypersalivation, waterbrash and excessive perspiration. 

A variety of stimuli may produce nausea (labyrinthine stimulation, pain, unpleasant memories). The neural pathways mediating nausea are not known, but evidence suggests that they are the same pathways that mediate vomiting. During nausea, gastric tone and peristalsis are reduced. The tone of the duodenum and proximal jejunum tends to be increased, with frequent reflux of duodenal contents into the stomach. 

Vomiting occurs as the gastric contents are forcefully brought up to and out of the mouth. This occurs by forceful sustained contraction of the abdominal muscles at a time when the cardia of the stomach is raised and open and the pylorus is contracted. Elevation of the cardia eliminates the intra-abdominal portion of the esophagus and relaxes the lower esophageal sphincter. This allows the stomach contents to enter the esophagus. The act of vomiting is completed with rapid upward displacement of the diaphragm and reversal of thoracic pressure from negative to positive. The glottis closes, the soft palate rises, the mouth opens and the stomach contents are expelled. The control of vomiting consists of two anatomically and functionally separate units, a vomiting center and a chemoreceptor trigger zone. The vomiting center is in the reticular formation of the medulla and is excited directly by visceral afferent impulses (sympathetic and vagal) arising from the gastrointestinal tract and other peripheral trigger areas. These trigger areas are found in the pharynx, cardiac vessels, peritoneum, bile ducts, cortex and stomach. The chemoreceptor trigger zone is on the floor of the fourth ventricle, on the blood side of the blood-brain barrier. The chemoreceptor trigger zone is unable to cause vomiting without an intact vomiting center. 

Patients may complain of nausea and hypersalivation. With gastrointestinal causes of the nausea (and vomiting) there may be associated symptoms of heartburn or epigastric pain. Prior to vomiting, patients may retch (spasmodic, abortive respiratory movements with the glottis closed). 

History-taking should probe for precipitating factors, other symptoms that suggest the underlying cause, drug use and dietary habits. The history should also explore psychological trauma or disturbances of body image suggestive of anorexia nervosa. 

Physical examination is often normal. An abdominal mass may point to an underlying cause (e.g., gastric carcinoma). Prolonged vomiting may cause dehydration. 

Prolonged nausea, by itself, rarely has an organic origin. There are many causes of nausea and vomiting, including intracerebral problems (e.g., hydrocephalus, brain tumor), stimulation of the peripheral trigger areas (e.g., severe chest pain, pain from kidney stones), systemic disease (malignancy), medications and pregnancy. Upper gastrointestinal diseases (esophagitis, peptic ulcer disease, gastric carcinoma) are common. Early morning nausea and vomiting suggest pregnancy, gastroesophageal reflux disease, alcohol withdrawal, a metabolic cause (e.g., uremia) or a psychogenic origin. 

In approaching a patient with nausea and vomiting, one should look for and correct any underlying causes. Prolonged vomiting may cause dehydration and the patient may need to be rehydrated intravenously. Medications should be discontinued. 

There are many drugs that have anti-emetic actions. Antihistamines act on the vestibular apparatus as well as on the chemoreceptor trigger zone. Phenothiazines also exert their action on the chemoreceptor trigger zone. Metoclopramide and domperidone are both anti-emetics and gastric prokinetics (which stimulate the stomach to empty). Domperidone exerts its action on the chemoreceptor trigger zone, whereas metoclopramide also crosses the blood-brain barrier and affects the vomiting center. Cisapride, a newer gastric prokinetic, has no effect on the chemoreceptor trigger zone or vomiting center. Like the other prokinetic agents, it may improve nausea and vomiting if they are due to gastric stasis or gastroparesis.