vomiting It would be a rare individual indeed who went through life without experiencing vomiting — the forceful and uncontrollable expulsion of stomach or intestinal contents — whether due to illness, turbulent travel, or extreme disgust.

Vomiting may be preceded by nausea, which is often accompanied by increased autonomic nervous system activity, involving salivation, sweating, pallor, and low blood pressure. Just before vomiting occurs there are retrograde contractions in the upper small intestine and in the stomach which propel their contents up the oesophagus and into the mouth.

There is a vomiting ‘centre’ in the mid-brain which co-ordinates the complex neural reflexes that occur during vomiting. The centre may be activated by incoming fibres in the vagus nerves from the gut, by the vestibular system via auditory nerves, by higher centres in the central nervous system, and also by input from a ‘trigger zone’ in the brain stem that is responsive to chemical stimulation by drugs, acidosis, and hypoxia.

Causes, investigation, and management of vomiting

Intestinal infections from food poisoning, particularly that due to Staphylococcus aureus and Bacillus cereus, produce vomiting soon after ingestion of contaminated food. Other infections can cause vomiting along with diarrhoea — particularly acute viral gastroenteritis due to rotavirus and bacterial diarrhoeas. There is often a clue to the source of infection, especially if there are several sufferers after a common meal or a sequence of contacts. The diagnosis can usually be made by microbiological examination of faeces. These acute infections are usually self-limiting, although in some instances antibiotics may be appropriate.

Gastrointestinal obstruction

The outlet of the stomach may be obstructed, particularly following chronic duodenal ulceration or as a result of gastric cancer, and this often produces vomiting. Gastric emptying may also be impaired when there is nerve damage or muscle damage, such as in the neuropathy associated with diabetes mellitus. Obstruction of the small bowel can occur as a result of adhesions, fibrotic strictures associated with intestinal inflammation (Crohn's disease), or radiation enteritis. Obstruction can usually be confirmed by X-ray, although more detailed investigation may be required to identify the precise site of the obstruction, and surgery may then be required to relieve it.

Causes arising in the central nervous system

Vomiting may be stimulated by excessively unpleasant perceptions — distressing sights, disgusting smells, or extreme anxiety are well known causes; motion sickness is produced by neural mechanisms involving the vestibular apparatus in the inner ear. Disorders in the brain itself can cause vomiting, for example migraine, meningitis, and any of the causes of increased intracranial pressure. When the history of the illness and other signs and symptoms indicate raised intracranial pressure, a brain scan is usually required to search for a cause; lumbar puncture and examination of cerebrospinal fluid may be necessary if meningitis is suspected.

Metabolic disorders

A variety of produce vomiting, particularly those associated with acidosis, including kidney failure and uncontrolled diabetes with ketoacidosis. These can usually be diagnosed with appropriate blood tests.

Anti-cancer drugs and radiotherapy

commonly produce nausea and vomiting, as do other drugs active in the central nervous system, including opiate pain killers (morphine, heroin) and also alcohol. Progress has been made in the development of new anti-emetic drugs (emesis = vomiting), particularly the serotonin antagonists which are potent inhibitors of chemotherapy-induced vomiting.

The eating disorders

anorexia nervosa and bulimia, are frequently associated with vomiting, usually self-induced.

The vomiting which may accompany early pregnancy is a common experience, so far largely unexplained.

Whatever the cause, the effects of vomiting on the body follow from the loss of fluid and of the acid which the gastric juices normally contain. There can therefore be dehydration and disturbance of acid–base homeostasis, which have to be corrected if vomiting is persistent or severe.

Michael Farthing, and Anne Ballinger