1

What is the cause of nausea and vomiting?

The vomiting center is located in the medulla. It receives input from the chemoreceptor zone and gastrointestinal tract. The vomiting center may be activated by various stimuli, including medications, body motion, stimulation of the posterior pharynx, odors, and visual images.

2

What are the risk factors for postoperative nausea and vomiting?

Risk factors for postoperative nausea and vomiting (PONV) are related to patient characteristics, type of surgery, and anesthetic. The main patient characteristics that increase the risk of PONV are female gender (especially if pregnant or menstruating), prior history of PONV, history of motion sickness, and being a nonsmoker.

Operative procedures particularly associated with an increased incidence of PONV are laparoscopy, breast, strabismus, and ear-nose-throat procedures. Surgical duration >30 minutes also increases the risk of PONV.

General anesthesia entailing potent volatile agents, nitrous oxide, and intravenous opioids increases the risk of PONV, whereas use of a propofol-based general anesthetic reduces the incidence and severity of PONV. There is little benefit if propofol is used only as an induction agent and a significant benefit if it is used as a maintenance infusion. Etomidate is associated with an increased risk of PONV and should be used only when hemodynamic stability is of paramount importance.

The incidence of PONV is similar regardless of type of opioid administered; opioid-sparing techniques should contribute to a risk reduction of PONV. A meta-analysis showed that a single perioperative intravenous dose of 60 mg of ketorolac was associated with a potentially clinically significant opioid-sparing effect and a statistically significant reduction in PONV. Intravenous acetaminophen, which became available in the United States more recently, can be expected to result in similar improved outcomes. Regional anesthetic techniques (e.g., peripheral nerve blocks) without intravenous opioid supplementation are also effective in reducing the risk of PONV.

3

What are the incidence and implications of postoperative nausea and vomiting?

PONV is the most common postoperative complication and the leading cause of delayed discharge from the PACU. It has been estimated that 25%–30% of surgical patients experience PONV within 24 hours of surgery. In high-risk surgical patients, the incidence of PONV may be 70%–80%. The incidence of perioperative vomiting in children has been estimated to be twice that of adults. In one review of 8995 pediatric outpatient cases, 26 patients required admission for persistent nausea and vomiting, accounting for 36% of all unanticipated hospital admissions. PONV may contribute to high levels of patient discomfort, delayed PACU discharge, increased need for nursing care, and potential hospital admission. All of these factors may increase avoidable periprocedural cost and are a main cause of patient dissatisfaction.

4

What are the strategies to reduce the incidence and severity of postoperative nausea and vomiting?

The 2007 Society of Ambulatory Anesthesia Guidelines for the Management of Postoperative Nausea and Vomiting recommend the following strategies to reduce PONV:

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  Use of regional anesthesia with no or minimal intravenous opioid supplementation

  
  
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  Use of propofol for induction and maintenance of general anesthesia

  
  
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  Avoidance of nitrous oxide

  
  
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  Avoidance of volatile anesthetics

  
  
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  Avoidance or minimization of intraoperative and postoperative opioids

  
  
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  Avoidance or minimization of neostigmine given for muscle relaxant reversal

  
  
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  Administration of adequate hydration

  
  
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  Prophylactic administration of 5-HT ₃ antagonists

  
  
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  Prophylactic administration of additional antiemetic medications to high-risk patients

5

What are the treatment considerations for postoperative nausea and vomiting?

Although there may be no consensus to administer antiemetic prophylaxis to all surgical patients, routine administration of some generically available agents is commonplace because of their minimal cost and risk. Considerations to administer pharmacologic antiemetic prophylaxis and treatment of established PONV should be individualized based on the previously discussed risk factors. Patients with several risk factors frequently require more than one agent. The following drugs are commonly administered either prophylactically or as treatment. They are listed in order of clinical usefulness and ease of use-to-risk ratio: 5-HT ₃ receptor antagonists, dexamethasone, droperidol, scopolamine, and metoclopramide.

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  Ondansetron, dolasetron, granisetron, and palonosetron are currently available 5-HT ₃ receptor antagonists approved for the prevention of PONV; ondansetron is the most widely studied. There is no significant difference in efficacy among these drugs when comparing equipotent doses. The recommended adult dose of ondansetron is 4 mg intravenously. Ondansetron is effective when administered after general anesthesia induction or approximately 30 minutes before the end of surgery. 5-HT ₃ receptor antagonists are the first choice for prophylaxis in children. Although frequently administered to treat established PONV, they are not effective if already administered prophylactically within the previous 4 hours. They all have minimal, if any, clinically significant side effects; however, there have been reports of Q–T interval prolongation similar to that seen with droperidol.

  
  
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  Dexamethasone is a potent synthetic glucocorticoid (0.75 mg of dexamethasone is equivalent to 20 mg of hydrocortisone). It is usually administered prophylactically in a dose of 4–10 mg intravenously after induction of general anesthesia. Administration may be associated with acute vaginal burning in awake female patients and with scrotal burning in male patients, which can be quite disturbing. Routine administration should be standard after induction of general anesthesia. Some studies have suggested that smaller doses (4 mg) are as effective as larger doses. The antiemetic mechanism of action is not well understood. No clinically significant adverse events have been noted after a single bolus dose of dexamethasone but caution is warranted in diabetic patients who are prone to hyperglycemia. The effectiveness of dexamethasone in treating established PONV is not nearly as well documented as the prophylactic effect.

  
  
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  Droperidol is a pharmacologic relative of the more widely used antipsychotic drug haloperidol. It is a potent α-adrenergic antagonist. In small doses (0.625–1.25 mg intravenously), it significantly decreases the incidence of PONV. When given in higher doses, it may be associated with excessive sedation and delayed discharge from the PACU. In 2001, the U.S. Food and Drug Administration (FDA) issued a “black box” warning noting that droperidol can cause Q–T interval prolongation, has been associated with lethal arrhythmias (e.g., torsade de pointes), and should not be administered in the presence of known Q–T interval prolongation. In the absence of a prolonged Q–T interval, it was recommended that patients receiving droperidol should have electrocardiogram (ECG) monitoring for 2–3 hours after administration. The FDA was widely criticized for these warnings and recommendations because this decision was mostly based on reported cases involving much higher doses of the drug than were clinically used in the United States and that low doses had not been associated with arrhythmia or cardiac arrest. Nonetheless, the “black box” warning has contributed to a significant reduction in the use of droperidol for prevention and treatment of PONV. However, in high-risk patients, early administration of droperidol allows for the requisite ECG monitoring period while conferring significant reduction in the risk of PONV.

  
  
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  Scopolamine is an anticholinergic drug that is usually applied as a transdermal patch and is better known for the prevention of motion sickness. It reduces PONV with minimal side effects but should be applied well before the induction of general anesthesia. Intramuscular or intravenous administration is much more likely to cause a central cholinergic syndrome consisting of sedation, amnesia, and euphoria. Consequently, intramuscular and intravenous routes of delivery are less desirable. The transdermal patch may be associated with complaints of dry mouth and visual disturbances.

  
  
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  Metoclopramide is a methoxychlorinated derivative of procainamide and is a dopamine antagonist. It is the weakest of all of the medications discussed here, and its ability to prevent PONV or treat established PONV has been questioned. Its antiemetic effect results primarily from increasing gastric emptying and lowering esophageal sphincter pressure. Although it may be administered orally and intramuscularly, 10 mg administered intravenously is the standard clinical dose. Extrapyramidal effects are common and frequently very disturbing to patients. Its poor efficacy and substantial side effects have led many clinicians to abandon the use of metoclopramide. It is not even mentioned in the 2007 SAMBA guidelines for the management of PONV.

  
  
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  Aprepitant is a newer NK ₁ receptor antagonist that is very expensive and not widely used by anesthesiologists.

Administration of intraoperative fraction of inspired oxygen (F io ₂ ) of 0.8 and postoperative supplemental oxygen (F io ₂ >0.3) has been associated with decreased PONV in patients receiving general anesthesia; this may be the result of eliminating nitrous oxide administration rather than increasing oxygen concentration. Other nonpharmacologic therapies that are effective include the following:

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  Acupuncture

  
  
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  Acupoint stimulation via wristband

  
  
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  Acupressure

Combining available therapies in management of PONV has been shown to be highly effective, with vomiting rates approaching 0% versus 7% with ondansetron alone and 22% with placebo. Although gastric suctioning before the completion of surgery empties the stomach and theoretically would reduce the incidence of PONV, this has not been shown to be efficacious.