PATHOPHYSIOLOGY: Vomiting is a defense mechanism used by the body to rid itself of toxic substances. Vomiting is a reflex primarily controlled by the vomiting center of the medulla of the brain, which receives sensory signals from the digestive tract, the inner ear, and the chemoreceptor trigger zone (CTZ) in the cerebral cortex. Interestingly, the CTZ is not protected by the blood–brain barrier, as is the vast majority of the brain; thus, these neurons can directly sense the presence of toxic substances in the blood. Once the vomiting reflex is triggered, wavelike contractions of the stomach quickly propel its contents upward and out of the body.
OBJECTIVES OF THE TREATMENT: The treatment outcomes for nausea or vomiting focus on removal of the cause, whenever feasible.
CAUSES OF NAUSEA AND VOMITING: Nausea and vomiting are common symptoms associated with a wide variety of conditions such as GI infections, food poisoning, nervousness, emotional imbalances, motion sickness, and extreme pain. Other conditions that promote nausea and vomiting are general anesthetics, migraine headache, trauma to the head or abdominal organs, inner ear disorders, and diabetes. Psychological factors play a significant role, as patients often become nauseated during periods of extreme stress or when confronted with unpleasant sights, smells, or sounds. The nausea and vomiting experienced by women during the first trimester of pregnancy is referred to as morning sickness. If this condition becomes acute, with continual vomiting, it may lead to hyperemesis gravidarum, a situation in which the health and safety of the mother and developing baby can become compromised. Pharmacotherapy is initiated after other antinausea measures have proved ineffective. Nausea and vomiting are the most frequently listed adverse effects for oral medications.
CONSEQUENCES OF NAUSEA AND VOMITING: Nausea and vomiting is a common reason for patients’ lack of adherence to the therapeutic regimen and for discontinuation of drug therapy. When large amounts of fluids are vomited, dehydration and significant weight loss may occur. Because the contents lost from the stomach are strongly acidic, vomiting may cause a change in the pH of the blood, resulting in metabolic alkalosis. With excessive loss, severe acid–base disturbances can lead to vascular collapse, resulting in death if medical intervention is not initiated. Dehydration is especially dangerous for infants, small children, and older adults and is evidenced by dry mouth, sticky saliva, and reduced urine output that is dark yellow-orange to brown.
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