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What is PONV?
The onset of nausea or vomiting within 24 hours of surgery is classified as post operative nausea and vomiting. Receptors within the vomiting center, which is the region of the medulla responsible for triggering vomiting, are activated by stimulation of afferent pathways. The cause of the stimulation is a combination of the surgery itself, as well as the effects of the anesthesia. About 20 to 30 percent of patients experience PONV.1 Patients with known risk factors are more likely to experience PONV.
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Factors that Contribute to PONV
Factors which contribute to post operative nausea and vomiting can be categorized into three groups. The first set of factors involve the patient. Female, non-smokers with a history of PONV or motion sickness are much more likely to experience PONV. The second group of factors involve the type of anesthetics used during the surgery. Patients receiving general anesthesia, high doses of neostigmine, or opioids have a high risk of developing PONV.1 The final factor contributing to PONV is the duration of the surgery. The longer it takes to complete the surgery, the more likely it is for the patient to develop PONV.
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Several steps can be taken prior to surgery to reduce the risk of PONV. If applicable, regional anesthesia should be used instead of general anesthesia. In cases where general anesthesia is required, administering propofol as the induction agent beforehand reduces the risk of PONV. Using non-steroidal anti-inflammatory drugs instead of opioids reduces the risk as well. Supplemental oxygen and intravenous fluid given before surgery can decrease the severity of PONV.1
A prophylactic drug regimen, usually given after surgery, targets the afferent pathways and receptors in the vomiting center to prevent the onset of nausea and vomiting. Such drugs are called antiemetic. Ondansetron, dimenhydrinate, dolasetron, droperidol and dexamethasone all have antiemetic properties. The most effective combination include a 5-HT3 (serotonin) receptor antagonist, such as ondansetron or dimenhydrinate, with droperidol or dexamethasone.1
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Treatment of PONV
If the preventive measures fail, additional factors must be considered before treating PONV. Patient-controlled pain management with morphine, an abdominal obstruction, and the presence of blood in the pharynx can cause nausea and vomiting. If this is not the case, PONV can be treated with a different class of antiemetics than those used prophylactically. If the patient has a low risk for developing PONV, prophylaxis isn't administered prior to surgery. In this case, a 5-HT3 receptor antagonist can be used at the onset of symptoms following surgery.1
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1. http://www.sogc.org/guidelines/documents/gui209CPG0807.pdf McCracken, Geoff et.al. "Guidelines for the Management of Postoperative Nausea and Vomiting." Society of Obstetricians and Gynecologists of Canada Clinical Practice Guidelines. No. 209, Jul. 2008. Web. 21 Apr. 2010.
2. http://www.ncbi.nlm.nih.gov/pubmed/16717343 Gan, TJ. "Risk Factors for Postoperative Nausea and Vomiting." National Center for Biotechnology Information. Jun. 2006. Web. 21 Apr. 2010.