Patient Factors
- Female gender (x3 risk - biggest risk factor)
- Younger age
- Non-smoker
- History of PONV previously
- History of Motion sickness
- Preoperative anxiety
- Disease states:
- Uraemia
- Intestinal obstruction
- Hypoglycaemia
- Hypoxia
Anaesthetic Factors
- Use of specific drugs:
- Inhalational agents (2x risk, dose dependent)
- Nitrous oxide (1.4x risk, likely due to GIT / middle ear cavity distension)
- Opioids (note untreated pain is also emetogenic)
- Sympathomimetics
- Etomidate, ketamine, methohexitone (compared with propofol and thiopentone)
- Neostigmine (recent work suggests that this is not associated with PONV)
- Prolonged anaesthesia
- Spinal anaesthesia (blocks above T5)
- Intraoperative dehydration
- Inexperienced bag and mask ventilation (gastric dilatation)
Surgical Factors
- Specific surgery types:
- Abdominal surgery
- Laparoscopic surgery
- Intracranial surgery
- Middle ear surgery
- Squint surgery (highest incidence of PONV in children)
- Gynaecological
- Head and neck surgery - especially tonsillectomy and adenoidectomy
- Other surgical factors:
- Prolonged surgery
- Painful surgery