Postoperative nausea and vomiting (PONV) remains a common clinical problem that increases patient morbidity, healthcare costs and affects patient satisfaction. This article outlines the physiology, reviews the available drugs and suggests a structure using risk stratification that helps to plan sensible clinical management.Postoperative nausea and vomiting (PONV) has an incidence of up to 30% 1,2 and is one of the most feared side effects of anaesthesia, even above pain. 3 Although in most cases it is self-limiting, each episode of vomiting delays discharge from the recovery room, increases the risk of unplanned admission and may be associated with more severe complications including pulmonary aspiration, dehydration, electrolyte abnormalities, raised intra-cranial and intraocular pressures, wound dehiscence and oesophageal rupture.The management of PONV involves risk stratification, prevention and treatment. This can utilize both pharmacological and non-pharmacological interventions.
DefinitionsNausea is the sensation of needing to vomit, which may include activation of central, sympathetic and parasympathetic responses.Vomiting is the involuntary oral expulsion of gastric contents via coordinated autonomic, gastrointestinal and respiratory system activity. It can be considered in two phases. In the pre-ejection phase, sympathetic activation causes tachypnoea, tachycardia, hypertension, diaphoresis, pallor and hypersalivation. During the ejection phase, the epiglottis closes and forceful coordination of diaphragm, abdominal musculature and oesophagogastric constrictors leads to forceful expulsion of gastric and upper duodenal contents.
Pathophysiology of nausea and vomitingThe physiology of nausea and vomiting is complex and new pathways remain to be discovered. A good understanding of current knowledge helps explain the pharmacological targets and therapies detailed below. Two key areas of the brain are important in the action of vomiting: the vomiting centre and the chemoreceptor trigger zone (CTZ) (Figure 1).
The vomiting center (VC)This lies in the lateral reticular formation of the medulla and receives afferent impulses via cranial nerves (CN) from the vestibulocochlear apparatus of the middle ear (CN VIII), carotid baroreceptor impulses (CN IX), gastrointestinal chemo-and stretch receptors (CN X) and aortic baroreceptors (CN X). It also receives afferents from higher cortical centres involved in pain, anticipation, memory, sight and fear as well as spinal cord afferents from peripheral pain pathways.The VC coordinates actions of the smooth and striated muscles involved in vomiting via the 'special visceral efferent nerves', CN V, VII, IX, X and XI. These innervate the muscles of the face, neck and oropharynx in a coordinated fashion. Motor, sympathetic and parasympathetic outflow to the gastrointestinal tract and secretory organs are carried by the autonomic general visceral efferents of CN II, VII, IX and X. Finally efferent branches from the VC travel via spinal nerves to the diaphragm and abdominal musc...