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Palliative cancer care - nausea & vomiting - Background information
What are nausea and vomiting?
- Nausea is an unpleasant sensation of the need to vomit, which is often accompanied by autonomic symptoms (e.g. pallor, cold sweat, salivation, and tachycardia) [Twycross and Wilcock, 2001; Kinley, 2005].
- Retching is a strong, involuntary effort to vomit, which usually occurs in the presence of nausea. It involves movement of the diaphragm and abdominal muscles against a closed glottis [Twycross and Wilcock, 2001; Kinley, 2005].
- Vomiting (emesis) is the forceful ejection of stomach contents through the mouth. The diaphragm and abdominal muscles contract and increase intra-abdominal pressure, compressing the stomach. The stomach, oesophageal sphincter, and pylorus relax, allowing reverse peristalsis and forcing the stomach contents upwards [Twycross and Wilcock, 2001; Kinley, 2005; Perdue, 2005].
- The vomiting process can be triggered by:
- The chemoreceptor trigger zone (CTZ), which is situated in the brain in the floor of the fourth ventricle, in the area postrema. The CTZ lies partly outside the blood–brain barrier, allowing exposure to water-soluble chemicals in the blood and cerebrospinal fluid (e.g. toxins, biochemical products, and drugs) which stimulate its chemoreceptors [Perdue, 2005; Mannix, 2006].
- The vomiting centre, which is situated in the brainstem and coordinates the vomiting process. The vomiting centre receives nerve signals from the CTZ, vestibular apparatus, higher cortical centres (e.g. fear, pain, memory), and other pathways (e.g. from liver capsule stretch by metastatic disease, peritoneal distortion from lymphadenopathy, or bowel dilatation because of obstruction or constipation). Impulses are sent from the vomiting centre to the pharynx, larynx, diaphragm, intercostal muscles, and gut, causing nausea, salivation, pallor, sweating, retching, protective glottis closure, and vomiting [Perdue, 2005; Mannix, 2006].
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