Female>male (x3). Incidence increases during menstruation and decreases after the menopause. After 70 years of age, both sexes are equally affected.
Obese (has been suggested, although there is currently insufficient evidence to conclude an association).
Young. Risk of PONV is almost twice that for adults. Equal distribution between boys and girls until puberty.
Previous history of PONV/motion sickness
Early ambulation, early postoperative eating and drinking.
Intracranial, middle ear
Squint surgery (highest incidence of PONV in children)
Gynaecological, especially ovarian
Head and neck, especially tonsillectomy and adenoidectomy (suggested due to blood in upper gastrointestinal tract (GIT), stimulation of trigeminal nerve afferents and peroperative opioids).
Opioids (NB untreated pain is also emetogenic)
Inhalational agents (Isoflurane++)
Etomidate, ketamine, methohexitone (compared with propofol and thiopentone)
Neostigmine (recent work suggests that this is not associated with PONV)
Nitrous oxide (GIT distension/expansion of middle ear cavities).
Spinal anaesthesia (blocks above T5), hypotension.
Inexperienced bag and mask ventilation (gastric dilatation).
Metabolic, e.g. hypoglycaemia