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Vomiting is a coordinated motor response of the gastrointestinal tract, abdominal muscles, and thoracic muscles that results in the forceful expulsion of stomach contents. Vomiting must be differentiated from regurgitation, which is the effortless expulsion of gastric contents through the mouth (discussed in Chapter 394).1 Vomiting is a common presenting symptom in acute and chronic disorders of both gastrointestinal and nongastrointestinal origin. Evaluation and management requires consideration of a broad differential diagnosis, recognition of alarm symptoms requiring immediate intervention, treatment aimed at the symptom and/or cause, and prevention of potential complications.


The physiological role of vomiting is to provide rapid clearance of ingested toxins.2 This patterned response often combines repeated emetic and diarrheal events that act efficiently to clear the entire intestinal tract of toxins in both orad and aboral directions.3 Vomiting consists of three distinct phases that may each occur independently: (1) Nausea is the sensation of impending vomiting, often associated with autonomic symptoms of pallor, diaphoresis, salivation, and anorexia. (2) Retching represents the spasmodic respiratory movements against a closed epiglottis. (3) Emesis is the retrograde expulsion of gastrointestinal contents through the mouth.

The act of vomiting is an integrated gastrointestinal and thoracoabdominal muscular response to noxious stimuli; it is coordinated by a central nervous system program.4 The gastrointestinal tract becomes atonic, the gastric fundus relaxes, and intestinal contents are swept into the stomach by a single retrograde contraction of the small intestine.5 Concerted rhythmic contractions of the respiratory, abdominal, and pharyngeal musculature increase intra-abdominal and intrathoracic pressure and either contract against a closed glottis in the case of retching or expel the gastric contents though the pharynx and out the mouth in the case of vomiting.6-8

Afferent stimulation of the vomiting center initiates the programmed, integrated motor responses just described as well as vasomotor activity (tachycardia and pallor) and hypersalivation. The vomiting center is not one locus but comprises the nucleus solitarius and a series of nearby nuclei in the brainstem medulla.9-11 Afferent input may arise from the posterior pharynx (eg, gagging), gastrointestinal tract (eg, bowel obstruction, inflammation), brain (eg, stress, increased intracranial pressure), or via circulation. Blood-borne substances such as apomorphine, opiates, cytotoxins, ammonia, and ketonesstimulate the chemoreceptor trigger zone in the area postrema, which lies outside the blood-brain barrier on the floor of the fourth ventricle.12 Neurotransmitters and their receptor subtypes (medications shown in parenthesis) that play a physiological role in vomiting include dopamine D2 (metoclopramide), histamine H1 (meclizine), serotonin 5-hydroxytryptamine3 (ondansetron), γ-aminobutyric acid (diazepam), vasopressin, and substance P (aprepitant).

Clinical Features and Differential Diagnosis

The evaluation of vomiting begins by distinguishing vomiting from other common disorders, such as regurgitation, and recognizing the temporal (acute-recurrent, chronic-recurrent, episodic, or cyclic) pattern of vomiting, as shown in eTable 382.1.13,14 Vomiting and regurgitation ...

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