ABSTRACT
Nausea and vomiting are hazards of both general and regional anaesthesia. Post-operative nausea and vomiting (PONV) can be extremely distressing and some studies have found it to be as distressing as pain. Nausea is the sensation of the need to vomit. Vomiting is the involuntary, forceful expulsion of gastric contents via the mouth. The physiology of vomiting is complex with multiple afferent and efferent pathways; an overview is helpful. The chemoreceptor trigger zone (CTZ) lies in the floor of the fourth ventricle in the area postrema and is functionally outside of the blood–brain barrier. The CTZ provides efferent input to the vomiting centre, which is located in the medulla. The vestibular system, peripheral pain pathways, intestinal chemoreceptors and the cerebral cortex all provide direct afferent input to the vomiting centre via cranial nerves VIII, IX and X. Vomiting is an involuntary reflex and may be divided into two phases, a preejection phase and ejection phase.
