Among all of the symptoms that are dreaded by patients receiving chemotherapy, nausea and vomiting are thought to become at the very top of the list. It's thought that 70% to 80% of patients receiving chemotherapy possess some level of nausea and vomiting. Nausea often precedes vomiting and it is a distressing feeling of the need to vomit. It's a separate event from vomiting and could or might not result in vomiting.
Retching, also called dry heaves, is yet another phenomenon that might accompany emesis. It's caused by the rhythmic contraction of the abdominal and respiratory muscles. Vomiting may be the forceful expulsion of the gastric contents with the mouth. It's combined with weakness, pallor, tachycardia, decreased blood pressure level, and increased respiration.
The precise mechanism of chemotherapy-induced emesis isn't completely understood. It's postulated that emesis is induced by stimulation of the true vomiting center, the nucleus tractus solitarius, located in the general area of the lateral reticular formulation of the fourth ventricle. The physiologic stimulation of the TVC is mediated by neurotransmitters, including serotonin, dopamine, norepinephrine, and histamine. The receptor sites of these transmitters can be found in the chemoreceptor trigger zoneand the GI tract. The TVC receives afferent impulses from four sources:
The CTZ, located in the area postrema in the brain stem, responds straight to volatile organic compounds in the blood and also the cerebrospinal fluid. The GI tract in the level of the small intestine may be the primary location of the serotonin receptor, that when stimulated sends impulses by sympathetic and afferent pathways. The larger cortical centers transmit psychogenic stimuli. The vestibular apparatus of the middle ear can also be involved.
When impulses from the of those four trigger points exceed the threshold, vomiting occurs. Patient characteristics and prognostic factors that modify the incidence of nausea and vomiting include:
Anxiety, expectations of severe negative effects, and previous chemotherapy experience are also predisposing factors. Intake of food, change in taste sensations, and also the quantity of sleep before chemotherapy can impact the incidence of nausea and vomiting. Patterns of chemotherapy-induced emesis are anticipatory, acute, delayed, and refractory.
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