Postoperative nausea and vomiting (PONV) is the phenomenon of nausea, vomiting, or retching experienced by a patient in the postanesthesia care unit (PACU) or within 24 hours following a surgical procedure. PONV affects about 10% of the population undergoing general anaesthesia each year. PONV can be unpleasant and lead to a delay in mobilization and food, fluid, and medication intake following surgery. Cause Emetogenic drugs commonly used in anaesthesia include nitrous oxide, physostigmine, and opioids. The intravenous anaesthetic propofol is currently the least emetogenic general anaesthetic. These medications are thought to stimulate the chemoreceptor trigger zone. This area is on the floor of the fourth ventricle and is effectively outside of the blood-brain barrier, which makes it incredibly sensitive to toxin and pharmacological stimulation. Several neurotransmitters are known, such as histamine, dopamine, serotonin, acetylcholine, and the more recently discovered neurokinin-1 (substance P). Risk factors A 2008 study compared 121 Japanese patients who experienced PONV after being given the general anesthetic propofol to 790 people who were free of postoperative nausea after receiving it. Those with a G at both copies of rs1800497 were 1.6 times more likely to experience PONV within six hours of surgery compared to those with the AG or AA genotypes, but they were not significantly more likely to experience PONV more than six hours after surgery. PONV results from patient, surgical, and anesthetic factors. Surgical factors that confer increased risk for PONV include procedures of increased length and gynecological, abdominal, laparoscopic and ENT procedures, and strabismus procedures in children. Anesthetic risk factors include the use of volatile anesthetics, nitrous oxide (N2O), opioids, and longer duration of anesthesia. Patient factors that confer increased risk for PONV include female gender, obesity, age less than 16 years, past history of motion sickness or chemotherapy-induced nausea, high levels of preoperative anxiety, and patients with history of PONV. Smokers and the elderly often have a decreased risk for PONV. A risk-stratification method created by Apfel et al has been developed to determine a patient's risk for PONV. The presence of 0, 1, 2, 3, or 4 of any of the following risk factors corresponds to a PONV respective risk of 10, 20, 40, 60, and 80%. - Female gender - Non-smoking - History of PONV or motion sickness - Expectant use of postoperative opioid medications Prevention Treatment options to prevent PONV include medications such as antiemetics (for example, ondansetron or dexamethasone)