ACUTE AND CHRONIC VOMITING
Vomiting is an involuntary, 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 389). In the context of human evolution, the ability to vomit serves as a protective mechanism to rid the body of ingested toxins. Vomiting can also be a common presenting symptom in acute and chronic disorders of either gastrointestinal or nongastrointestinal origin. Evaluation and management require 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. Vomiting consists of 3 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 coordinated by a central nervous system program. 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. 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 forcefully expel the gastric contents though the pharynx and out the mouth, in the case of vomiting.
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 comprises the nucleus solitarius and a series of nearby nuclei in the brain stem medulla. Afferent input may arise from the posterior pharynx (eg, gagging), gastrointestinal tract (eg, bowel obstruction, inflammation), or brain (eg, stress, increased intracranial pressure), or via circulation. Blood-borne substances such as apomorphine, opiates, cytotoxins, ammonia, and ketones can stimulate the chemoreceptor trigger zone in the area postrema, which lies outside the blood–brain barrier on the floor of the fourth ventricle. Neurotransmitters and their receptor subtypes that play a physiological role in vomiting include the following (medications to control nausea and vomiting are shown in parentheses): 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 (Table 377-1). Vomiting and regurgitation can occur concomitantly in gastroesophageal reflux, but they ...