7.5 Antiemetics
This section will review the pathophysiology of nausea and vomiting and then apply the nursing process to administering antiemetic medications.
Review of the Pathophysiology of Nausea and Vomiting
Nausea and vomiting are common conditions. Nausea is the unpleasant sensation of having the urge to vomit, and vomiting (emesis) is the forceful oral expulsion of gastric contents.[1] There are many potential causes of nausea and vomiting, such as the following:
- Morning sickness during pregnancy
- Gastroenteritis and other infections
- Migraines
- Motion sickness
- Food poisoning
- Side effects of medicines, including those for cancer chemotherapy
- GERD and ulcers
- Intestinal obstruction
- Poisoning or exposure to a toxic substance
- Diseases of other organs (cardiac, renal, or liver)
Nausea and vomiting are common and are usually not serious. However, the health care provider should be contacted immediately if the following conditions occur:
- Vomiting for longer than 24 hours
- Blood in the vomit (also called hematemesis)
- Severe abdominal pain
- Severe headache and stiff neck
- Signs of dehydration, such as dry mouth, infrequent urination, or dark urine
Treatment of nausea and vomiting should be tailored to the cause. There are several medications that work on different neuroreceptors that when used can treat nausea and vomiting. For severe cases of vomiting, intravenous fluids may also be needed to treat the accompanying dehydration.[2],[3]
The Vomiting Center and Associated Neurotransmitters
The vomiting center can be activated directly by irritants or indirectly following input from four principal areas: gastrointestinal tract, cerebral cortex and thalamus, vestibular region, and chemoreceptor trigger zone (CRTZ). See Figure 7.18 for an illustration of the pathophysiology of nausea and vomiting.[4]
An important part of the emesis circuit is the chemoreceptor trigger zone (CTZ), located in the area postrema in the brain. The CTZ is not restricted by the blood–brain barrier, which allows it to respond directly to toxins in the bloodstream such as anesthesia and opioids. The CTZ also receives stimuli from several other locations in the body, including the vestibular center; visceral organs such as the GI tract, kidneys, and liver; the thalamus; and the cerebral cortex.
The vestibular center and cerebral cortex can stimulate the vomiting center directly or indirectly through the CTZ. The vestibular system is located within the inner ear and gives a sense of balance and spatial orientation for the purpose of coordinating movement with balance. The feeling of nausea associated with motion sickness often arises from stimuli from the vestibular center. The gastrointestinal tract sends stimuli to the CTZ via cranial nerves IX and X related to obstruction, distension, inflammation, and infection. The cerebral cortex and other parts of the brain can also stimulate a sense of nausea related to odors, tastes, and images and send these stim