I. INTRODUCTION

Postoperative nausea and vomiting (PONV) continues to be a common occurrence in the postanesthesia care unit (PACU) setting, affecting at least 30% of patients after general anesthesia and greater than 80% in populations with multiple risk factors without prophylaxis. The sequelae of PONV range from the relatively benign (patient discomfort and poor patient satisfaction) to the more severe (electrolyte abnormalities, dehydration, pain especially with abdominal and thoracic surgery, wound or anastomotic dehiscence, hypertension, increased intracranial pressure, pneumothorax, and aspiration). PONV is also a major contributor to PACU length of stay, limiting discharge for ambulatory surgery and increasing hospital admission rates, costing hundreds of millions of dollars per year in the United States alone. Therefore, prevention and treatment of PONV is of paramount importance. The focus of this chapter is to describe the risk factors related to PONV, discuss PONV prophylaxis and rescue, and summarize the therapies for PONV.

II. RISK FACTORS: PATIENT

Several studies have been undertaken to assess patient risk factors related to PONV, and several predictive models have been developed to help determine which patients would benefit most from PONV prophylaxis. Recent evidence-based analysis has shown that the following risk factors are most closely associated with PONV: female gender, history of PONV, nonsmoking status, history of motion sickness, and age.

A. Female gender is highly correlated with PONV, with a risk greater than 2.5 times that of males. The mechanism for this effect is, however, not well understood. Smaller trials have shown that females are more sensitive to emetogenic stimuli and 2 to 3 times more likely to suffer from PONV than men. This susceptibility is thought to be hormonally mediated because these studies suggest that females are 4 times more likely to suffer from PONV during menses and 4 times less likely to suffer from PONV after menopause compared with baseline. However, large randomized controlled trials have failed to support these variations in PONV susceptibility with hormonal cycles.

B. Patients who have a history of PONV after prior surgeries are approximately 2 times more likely to suffer from PONV from subsequent surgeries than the general population. In addition, a history of motion sickness is thought to indicate a susceptibility to PONV that may be genetically mediated because sufferers of motion sickness and PONV are more likely to have first-degree relatives with their own history of PONV compared with controls.

C. Nonsmokers are approximately 2 times more likely to suffer from PONV than smokers. The protective action of smoking on PONV is currently unknown; however, many diverse hypotheses have been generated and await testing. Induction of cytochrome P450 by cigarette smoke
contaminants has been shown to lead to increased anesthetic gas metabolism, although the small change in metabolism is unlikely to account for the marked differences in PONV susceptibility between smokers and nonsmokers. Another hypothesis is that smoking and nicotine alter the neurotransmitter milieu responsible for PONV.

D. Age has been shown to be protective for PONV, with approximately a 20% risk reduction with each decade of life. PONV, however, is relatively uncommon in children aged less than 3, but is more prevalent in adolescence and early adulthood before decreasing with increasing age. The mechanism of this trend is unknown; however, several hypotheses have been proposed, including hormonal variations in adolescence and puberty and reduced autonomic reflexes in the aged adult.

III. RISK FACTORS: SURGERY

Evidence for the impact of surgical type on PONV is limited by publication bias; however, there is a strong historical consensus on high-risk surgeries that are associated with PONV.

A. Ophthalmic surgeries, especially strabismus surgeries, are well known to cause dizziness and PONV.

B. ENT middle ear surgeries can lead to profound PONV, and ENT procedures with bleeding down the GI track can lead to emesis.

C. Gynecologic, urologic, and abdominal procedures can lead to visceral stimulation that is highly emetogenic. In addition, laparoscopic procedures with insufflation can cause visceral pressure and retained abdominal CO₂, causing PONV.

D. Other surgical factors that are less well studied but may still have a role in PONV include incisional pain, hypotension, hypoxia, ileus, and the presence of a nasogastric tube.

E. In addition, special care should be given to patients undergoing surgeries following which retching or vomiting would be highly detrimental, especially laryngeal/tracheal surgery, surgeries with vulnerable vascular anastomoses, or those during which intracranial hypertension is present.

IV. RISK FACTORS: ANESTHESIA

The type of anesthesia delivered has long been known to affect PONV, especially in susceptible populations. Recent meta-analysis suggests that the most strongly associated anesthesia risk factors for PONV are the use of volatile anesthetics, duration of anesthesia, use of nitrous oxide, and postoperative opioids.

A. Volatile anesthetics have been shown to be the strongest predictor of early PONV, and it is unsurprising that prolonged exposure to volatile anesthetics further increases the risk of PONV.

B. Nitrous oxide has been shown to be associated with PONV, especially when the duration exceeds 45 minutes to 1 hour. Proposed mechanisms of nitrous oxide-induced PONV include bowel distention, middle ear pressure changes, and direct effects on receptors in emetogenic centers in the brain.

C. Postoperative opioids are thought to cause PONV through peripheral µ-opioid receptor activation, leading to reduced peristaltic activity and to decreased gastric and colonic emptying and visceral distention.

V. PONV RISK SCORES AND PROPHYLAXIS

Medications used to treat PONV are not without side effects; therefore, many risk scores have been developed to stratify patients’ likelihood of developing PONV to help guide the choice of prophylaxis. Most of these assign points to known patient, surgical, and anesthesia risk factors (such as those listed above) and give approximate PONV risk
and suggestions for prophylaxis. There is continued debate as to the benefits of routine PONV prophylaxis given cost-effectiveness of treatment and possible medication side effects; however, in certain patient populations, it is warranted.