Nausea is usually defined as the inclination to vomit or as a feeling in the throat or epigastric region alerting an individual that vomiting is imminent. Vomiting is defined as the ejection or expulsion of gastric contents through the mouth, often requiring a forceful event.
Specific etiologies associated with nausea and vomiting are presented in Table Specific Etiologies of Nausea and Vomiting.
Emetogenesity of Chemotetherapeutic agents presents specific cytotoxic agents categorized by their emetogenic potential. Although some agents may have greater emetogenic potential than others, combinations of agents, high doses, clinical settings, psychological conditions, prior treatment experiences, and unusual stimuli to sight, smell, or taste may alter a patient’s response to a drug treatment.
|TABLE Specific Etiologies of Nausea and Vomiting|
|TABLE. Emetogenicity of Chemotherapeutic Agents|
A variety of other common etiologies have been proposed for the development of nausea and vomiting in cancer patients. These are presented in Table Nonchemotherapy Etiologies of Nausea and Vomiting in Cancer Patients.
The three consecutive phases of emesis include nausea, retching, and vomiting. Nausea, the imminent need to vomit, is associated with gastric stasis. Retching is the labored movement of abdominal and thoracic muscles before vomiting. The final phase of emesis is vomiting, the forceful expulsion of gastric contents due to gastrointestinal (gastrointestinal) retroperistalsis.
Vomiting is triggered by afferent impulses to the vomiting center, a nucleus of cells in the medulla. Impulses are received from sensory centers, such as the chemoreceptor trigger zone, cerebral cortex, and visceral afferents from the pharynx and gastrointestinal tract. When excited, afferent impulses are integrated by the vomiting center, resulting in efferent impulses to the salivation center, respiratory center, and the pharyngeal, gastrointestinal, and abdominal muscles, leading to vomiting.
The chemoreceptor trigger zone, located in the area postrema of the fourth ventricle of the brain, is a major chemosensory organ for emesis and is usually associated with chemically induced vomiting.
|TABLE. Nonchemotherapy Etiologies of Nausea and Vomiting in Cancer Patients|
Numerous neurotransmitter receptors are located in the vomiting center, chemoreceptor trigger zone, and gastrointestinal tract. Examples of such receptors include cholinergic and histaminic, dopaminergic, opiate, serotonin, neurokinin, and benzodiazepine receptors. It is theorized that chemotherapeutic agents, their metabolites, or other emetic compounds trigger the process of emesis through stimulation of one or more of these receptors.
Nausea and vomiting may be classified as either simple or complex. The term simple applies to those episodes of nausea and/or vomiting described by one of the following criteria: (1) occur occasionally and are self-limiting or relieved by the minimal use of antiemetic methods or medications; (2) account for slight patient deterioration such as fluid-electrolyte imbalances, pain, or noncompliance with prescribed therapies; or (3) are not related to the administration of or exposure to noxious agents.
The term complex is used when describing a patient’s clinical course as including symptoms that are not adequately or readily relieved by the administration of a single antiemetic method or medication; that lead to progressive patient deterioration secondary to fluid-electrolyte imbalances, pain, or noncompliance with prescribed therapies; or that are caused by noxious agents or psychogenic events.
Nausea and vomiting occur frequently after operative procedures; those of the abdomen, eye, ear, nose, and throat are generally associated with higher incidences of nausea and vomiting than other procedures. Women experience a threefold higher incidence of nausea and vomiting compared to men, independent of the type of operation or anesthetic. Children are about twice as susceptible as adults.
Other risk factors that may be associated with an increase in postoperative symptoms include patient variables such as obesity, increased age, a history of motion sickness or prior postoperative emesis, as well as drug therapy variables such as the choice of premedication or general anesthetic agent.
Many women experience nausea and vomiting during pregnancy; however, the etiology of hyperemesis gravidarum is not well understood.
The overall goal of antiemetic therapy is to prevent or eliminate nausea and vomiting; this should be accomplished without adverse effects or with clinically acceptable adverse effects.
Treatment of Nausea and Vomiting
Evaluation of therapeutic outcomes
Monitoring criteria for drug therapy includes the subjective assessment of the severity of nausea as well as objective parameters such as the number of vomiting episodes each day, the volume of vomitus lost, and evaluation of fluid, acid-base balance, and electrolyte status, with particular attention to serum sodium, potassium, and chloride concentrations. In addition, evaluation of renal function may become important, particularly in patients with volume contraction and progressive electrolyte disturbances. Specific parameters include daily urine volume, urine specific gravity, and urine electrolyte concentrations.
Physical assessment of patients should include evaluation of mucous membranes and skin turgor, since dryness of these tissues may be indicative of significant volume loss.