Nausea and vomiting are very common symptoms in the paediatric population. Whether presenting in the emergency department or in an outpatient clinic, they are a frequent reason for parents and caregivers to seek medical attention. As a result, they have a significant impact on healthcare costs.
Nausea is defined as the subjective unpleasant sensation of imminent vomiting. It is frequently accompanied by autonomic symptoms such as dizziness, pallor, and sweating.
Vomiting is defined as the vigorous oral expulsion of the gastric or intestinal contents associated with increased intra-abdominal pressure. Oral regurgitation refers to the effortless, usually postprandial, emesis of food content.
According to the Rome foundation, chronic nausea is defined as bothersome nausea occurring several times per week, not usually associated with vomiting, in the absence of endoscopic or metabolic disease. These criteria must be fulfilled for the last 3 months, with the symptom onset at least 6 months prior to diagnosis.  In the latest Rome IV consensus, a specific definition of chronic nausea for young children or adolescents was not included.  
Vomiting is usually preceded by nausea; the only exceptions are rumination syndrome, in which oral regurgitation is not preceded by nausea, and possibly gastro-oesophageal reflux disease (GORD). On the other hand, nausea is not always followed by vomiting, as in conditions such as chronic functional nausea, postural nausea, and functional dyspepsia.
There are various established mechanisms that are known to cause nausea and vomiting, including: 
Stimulation of chemoreceptors situated in the area postrema (medullary structure located in the fourth ventricle of the brain)
Movement-induced stimulation of the labyrinth
Irritation or over-distension of the mechanical-sensitive vagal afferents in the gastrointestinal tract.
The aetiology of nausea and vomiting is often age-dependent, with a wide spectrum of gastrointestinal, non-gastrointestinal, and environmental causes, including:
Inflammatory changes causing infection of the gastrointestinal system or other body systems
Anatomical abnormalities resulting in bowel obstruction
Functional disorders or malignancy of the gastrointestinal tract
Neurological causes, which can be one of the most ominous causes, particularly in the presence of increased intracranial hypertension or CNS infection
Metabolic or endocrine abnormalities such as diabetic ketoacidosis, adrenal insufficiency, and protein or carbohydrate metabolism disorders
Urological/gynaecological or renal causes such as gonadal torsion
Renal causes such as haemolytic uraemic syndrome and nephrolithiasis
Psychiatric causes such as eating disorders, rumination, or Munchausen's by proxy
Environmental causes such as toxic ingestions and adverse effects associated with the use of medications or illicit drugs.
A complete history and meticulous physical examination is essential and provides the clues for appropriate diagnosis and management. Diagnostic testing should be directed by the clinical picture. 
Urgent considerations, particularly neurological compromise, need to be addressed first and may prompt more immediate therapeutic management. Lethargy, fever, volume depletion, weight loss, bilious vomiting, haematemesis, papilloedema, abdominal tenderness, or the presence of a mass are red-flag symptoms that may require urgent management.
Professor of Pediatrics
Neurointestinal and Motility Program Director
Ann & Robert H. Lurie Children’s Hospital of Chicago
JEF declares that he has no competing interests.
Assistant Professor of Pediatrics
Duke University School of Medicine
MKRB is a consultant for Medspira on pediatric integration for anorectal manometry by assisting with training providers on device use, for which she receives no compensation at this time. There is no contractual agreement to disseminate product information. MKRB declares that she has no conflicting interest related to this topic.
Dr John E. Fortunato and Dr Mary K. Rogers Boruta would like to gratefully acknowledge Dr Roberto A. Gomez-Suarez, a previous contributor to this monograph. RAGS declares that he has no competing interests.
Division of General Pediatrics
Stanford School of Medicine
DAB declares that he has no competing interests.
Golisano Children's Hospital
Upstate Medical University
PDW declares that he has no competing interests.
Reader in General Paediatrics
Honorary Consultant Paediatrician
University College London Hospitals and Great Ormond Street Hospitals
Institute of Child Health
University College London
AGS is developing a project on the use of an antiemesis drug for gastroenteritis but has no other connection with the topic per se.
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