Postoperative nausea and vomiting
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# Overview
Postoperative nausea and vomiting (PONV) is an unpleasant complication affecting about a third of the 10% of the population undergoing general anaesthesia each year. This equates to about two million people in the United Kingdom annually.

# Impact
On average the incidence of nausea or vomiting after general anesthesia ranges between 25 and 30% . Nausea and vomiting can be extremely distressing for patients and is therefore one of their major concerns . Vomiting has been associated with major complications such as pulmonary aspiration of gastric content and might endanger surgical outcomes after certain procedures, for example after maxillofacial surgery with wired jaws. Nausea and vomiting can delay discharge and about 1% of patients scheduled for day surgery require unanticipated overnight admission because of uncontrolled postoperative nausea and vomiting.

# Management
Because no currently available antiemetic is especially effective by itself, and successful control is often elusive, experts recommend a multimodal approach. Anaesthetic strategies to prevent vomiting include using regional anaesthesia wherever possible and avoiding emetogenic drugs. Pharmacological treatment and prevention of postoperative nausea and vomiting is limited by both cost and the adverse effects of drugs. Patients with risk factors probably warrant prophylaxis, whereas a "wait and see" strategy is appropriate for those without risk factors.

# Pharmacology
The introduction of the 5HT3 receptor antagonist, ondansetron, in the early 1990s was a significant breakthrough. Despite the many studies, however, the evidence base to support rational antiemetic treatment remains patchy. Recent research has led to better understanding of some older drugs and has demonstrated that combinations of drugs are often useful. While the efficacy of droperidol is now clear, metoclopramide, a popular antiemetic for decades, has been found to have no worthwhile efficacy. Some older drugs, such as haloperidol and hyoscine remain inadequately studied.
Emetogenic drugs commonly used in anaesthesia include nitrous oxide, physostigmine and opioids. The intravenous anaesthetic propofol is currently the least emetogenic general anaesthetic.

# Risk factors
Postoperative nausea and vomiting results from anaesthesic, surgical, and patients factors. Gynaecological, urological, strabismus correction and middle ear surgery all have a higher risk of postoperative nausea and vomiting.
Patients that are female or who have a history of postoperative nausea and vomiting are at greater risk. Smokers have a decreased risk, but this would never be recommended by any physician. One study found that the increased risk in women was correlated to the phase of their menstrual cycle.