Nausea

Did You Know?

• Repeated intentional vomiting, characteristic of bulimia, can cause stomach acid to wear away at the enamel present on the teeth.
• Nausea, as opposed to vomiting, occurs most frequently in persons aged 15–24 years in Australia.

Causes

Acute nausea and vomiting are most often triggered by gastrointestinal infections or food poisoning. Medication side effects and pregnancy are also common culprits. Chronic nausea can stem from a range of digestive issues, including gastroesophageal reflux disease, functional dyspepsia, gastritis, biliary reflux, gastroparesis, peptic ulcer, celiac disease, non-celiac gluten sensitivity, Crohn's disease, hepatitis, upper gastrointestinal malignancy, and pancreatic cancer. An uncomplicated H. pylori infection does not lead to chronic nausea. Food poisoning typically brings on nausea and vomiting within one to six hours of eating contaminated food, lasting one to two days. Many drugs can cause nausea, notably chemotherapy agents, general anesthetics, and opioids. Morning sickness affects nearly 80% of women in the first trimester, though it can persist later. Balance disorders like motion sickness and vertigo, as well as dysmenorrhea, may also provoke nausea. Depression, anxiety, and eating disorders are additional potential causes. About 10% of nausea and vomiting cases remain unexplained. After childhood, doctor visits for nausea decline with age, and only a tiny fraction of visits by those over 65 are for this symptom.

Pathophysiology

The physiologic mechanism of nausea is a complex process that has yet to be fully elucidated. There are four general pathways activated by specific triggers. The central nervous system pathway involves the cerebral cortex and limbic system, activated by elevated intracranial pressure, irritation of the meninges, and extreme emotional triggers. The chemoreceptor trigger zone is located in the area postrema in the floor of the fourth ventricle, outside the blood brain barrier, and is activated by metabolic abnormalities, toxins, and medications via dopamine D2, serotonin 5HT3, and neurokinin NK1 receptors. The vestibular system is activated by disturbances to the inner ear, such as those causing motion sickness and dizziness, via histamine H1 and acetylcholine ACh receptors. Peripheral pathways are triggered by chemoreceptors and mechanoreceptors in the gastrointestinal tract and other organs, responding to toxins and distension, with signals traveling via the vagus, glossopharyngeal, splanchnic, and sympathetic nerves.

Diagnosis

Taking a thorough patient history may reveal important clues. Acute onset suggests drugs, toxins, or infections; a long-standing history points to chronic illness. Symptoms within an hour of eating may indicate obstruction proximal to the small intestine, such as gastroparesis or pyloric stenosis. Infectious causes may present hours to days after food ingestion. The contents of emesis provide clues: fecal matter indicates distal intestinal or colon obstruction; bilious emesis localizes obstruction past the stomach; undigested food points to obstruction before the gastric outlet. Reduced abdominal pain after vomiting suggests obstruction, while vomiting does not relieve pain from pancreatitis or cholecystitis. Signs of dehydration such as orthostatic hypotension and loss of skin turgor should be monitored. Auscultation may reveal high-pitched tinkling sounds indicating bowel obstruction or a splashing succussion sound suggesting gastric outlet obstruction. Papilledema, visual field losses, or focal neurological deficits are red flags for elevated intracranial pressure.

Treatment

When dehydration results from fluid loss due to heavy vomiting, the first step is to replace fluids with oral electrolyte solutions. If that fails or isn't possible, fluids may need to be given intravenously. A person should seek medical help if they can't keep down any liquids, have symptoms lasting more than two days, feel weak, develop a fever, have stomach pain, vomit more than twice in a day, or go more than eight hours without urinating. No single anti-nausea drug works best for everyone; the choice depends on the cause. For motion sickness or vertigo, antihistamines and anticholinergics like meclizine and scopolamine work well. Migraine-related nausea responds best to dopamine antagonists such as metoclopramide, prochlorperazine, and chlorpromazine. For gastroenteritis, serotonin antagonists like ondansetron help reduce nausea and vomiting and cut the need for IV fluids. The combination of pyridoxine and doxylamine is the first-line treatment for nausea in pregnancy. Dimenhydrinate is a cheap over-the-counter option for preventing nausea after surgery. Cannabinoids can help with nausea from chemotherapy, and ginger may also be effective for several types of nausea.