++
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.
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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
can occur ...