Chapter 5 NAUSEA AND VOMITING
INTRODUCTION
Nausea and vomiting are common symptoms with a wide array of possible causes. Nausea describes the unpleasant subjective sensations that precede vomiting. During nausea, reflux of duodenal contents into the stomach is frequent, possibly due to increased tone of the duodenum and proximal jejunum, although this is not always present. Concurrently, gastric tone is reduced and gastric peristalsis is diminished or absent. It is important to distinguish between four distinct symptoms, namely retching, vomiting, regurgitation and rumination, that superficially may appear similar (Table 5.1). In particular, vomiting involves expulsion of gastric contents through the mouth via forceful, sustained contraction of the abdominal muscles and diaphragm when the pylorus is contracted. Occasionally, vomiting is associated with hypersalivation and defecation; cardiac dysrhythmias may rarely occur.
TABLE 5.1 Definitions of terminology associated with nausea and vomiting
| Nausea: The unpleasant sensation of the imminent need to vomit, usually referred to the throat or epigastrium; a sensation that may or may not ultimately lead to the act of vomiting. |
| Retching: Spasmodic respiratory movements against a closed glottis with contractions of the abdominal musculature without expulsion of any gastric contents, referred to as ‘dry heaves’. |
| Vomiting: Forceful oral expulsion of gastric contents associated with contraction of the abdominal and chest wall musculature. |
| Regurgitation: The act by which food is brought back into the mouth without the abdominal and diaphragmatic muscular activity that characterises vomiting. |
| Rumination: Chewing and swallowing of regurgitated food that has come back into the mouth through an unconscious voluntary increase in abdominal pressure within minutes of eating or during eating. |
| Anorexia: Loss of desire to eat, that is, a true loss of appetite. |
| Sitophobia: Fear of eating because of subsequent or associated discomfort. |
| Early satiety: The feeling of being full after eating an unusually small quantity of food. |
Adapted from Quigley EM, Hasler WL, Parkman HP. AGA technical review on nausea and vomiting. Gastroenterology 2001; 120:263–86.
PATHOGENESIS
Neurotransmission in the vomiting centre and CTZ appears to be mediated via dopaminergic, serotonergic, muscarinic and histaminergic receptors, and pharmacological therapies have been developed targeting each of these (see later).
CLINICAL CONSIDERATIONS
The differential diagnosis of nausea and/or vomiting is extensive and is presented in Table 5.2. The major causes include infection, medications (particularly chemotherapeutic agents) and toxins, central nervous system pathology, organic gastrointestinal disorders, endocrine and metabolic disorders including pregnancy, systemic illnesses, psychiatric disease, postoperatively and functional gastrointestinal disorders including the cyclical vomiting syndrome.
| Medications and toxic aetiology |
