Postoperative nausea and vomiting

Risk factors Risk factors for PONV can be classified into three main categories: patient-related, surgical, and anesthetic-related. Patient-related Patient factors that confer increased risk for PONV include female gender, younger age (<16 years old), obesity, non-smoking status, high levels of preoperative anxiety, and prior history of PONV, motion sickness, or chemotherapy-induced nausea. The Apfel risk-scoring system is commonly used to sensitively and specifically determine the risk of PONV in adults. • Female sex (most reliable) • Non-smoking status • History of PONV or motion sickness • Post-operative opioid use The presence of 0, 1, 2, 3, or 4 factors corresponds to PONV risks of approximately 10%, 20%, 40%, 70%, and 80%, respectively. Research has also shown a genetic disposition towards PONV. Certain procedure types such as gynecological, abdominal, laparoscopic, ENT surgeries, and strabismus surgery in children are associated with a modestly increased risk of PONV versus other general surgical procedures. The approach taken to anesthesia may also play a role in the risk of nausea and vomiting post-operatively. A significant body of evidence indicates that total intravenous anesthesia (TIVA) using propofol for induction and maintenance can reduce the incidence of postoperative nausea and vomiting significantly in both adults and children (3.5-fold vs. 5.7-fold reduction respectively) in comparison to volatile-anesthetic based techniques. Regional anesthesia has also demonstrated better outcomes for patients when compared to its general counterpart. == Mechanism ==

The pathophysiology of PONV is mediated by several key neurotransmitters, including histamine, dopamine, serotonin, acetylcholine, and the more recently recognized neurokinin-1 (substance P). Pharmacologic stimulation of different chemoreceptors in the brain trigger different pathways that can result in PONV. Additionally, direct surgical manipulation of the vestibular system (cranial nerve VIII) or gastrointestinal structures innervated by the vagus nerve (cranial nerve X) can further activate the neural pathways involved in precipitating nausea and vomiting. == Prevention ==

Key strategies in the prevention of postoperative nausea and vomiting include diligent risk assessment and stratification, use of non-volatile anesthetic techniques when feasible, provision of preventative medications based on risk, and employment of multimodal, opioid-sparing techniques for surgical pain control. Optimizing intravascular fluid volume during surgery is another strategy to reduce the risk of PONV, often achieved by administering additional IV fluids under general anesthesia. This approach addresses the fluid deficit caused by preoperative fasting, which typically restricts oral fluid intake for 2–6 hours before surgery. There is some evidence that providing the person undergoing anesthesia with supplemental perioperative intravenous crystalloids may reduce vomiting and/or nausea in patients with certain characteristics (American Society of Anesthesiologists (ASA) class I and II patients). The potential risks and other adverse effects with this type of therapy are unknown. For minor surgical procedures, more research is needed to determine the risks and benefits of this approach. ==Management==

Commonly administered medications like serotonin receptor antagonists (ondansetron), corticosteroids (dexamethasone), and neurokinin-1 receptor antagonists (aprepitant) primarily act by modifying the release and activity of the aforementioned neurotransmitters involved in nausea and vomiting, effectively reducing the incidence of PONV. Using a multimodal approach by combining drugs targeting different receptors involved in PONV has been shown to be more efficacious than monotherapy. Medications • Serotonin (5-HT3) receptor antagonists can be administered as a single dose at the end of surgery. Adverse effects include prolongation of the QT interval on electrocardiogram (EKG). Medications include ondansetron, granisetron, and dolasetron. • Anticholinergics can be used as a long-acting patch placed behind the patient's ear. Adverse effects include dry mouth and blurry vision. Care must be taken when handling the patch, as transfer of medication to the eye can induce pupillary dilation. Avoid use in elderly patients. Medications include scopolamine. • Glucocorticoids have direct antiemetic effects and can reduce need for postoperative opioids. Adverse effects include a transient increase in serum glucose level, and poor wound healing (controversial). Medications include dexamethasone. • Butyrophenones are antipsychotic medications that are typically administered as a single injection at the end of surgery. Medications include droperidol and haloperidol, although droperidol is less frequently used as it may cause QT prolongation on EKG. Alternative therapies The management of perioperative pain using opioid-sparing multimodal analgesic techniques is critically important for reducing PONV incidence and achieving enhanced recovery after surgery. In addition to incorporating non-opioid analgesics like NSAIDs and acetaminophen, at least one study has found that application to the pericardium meridian 6 acupressure point produced a positive effect in relieving PONV. Another study found no statistically significant difference. The two general types of alternative pressure therapy are sham acupressure and the use of the P6 point. A 2015 study found no significant difference between the use of either therapy in the treatment or prevention of PONV. In a review of 59 studies, both therapies significantly affected the nausea aspect, but had no significant effect on vomiting. There is also some evidence suggesting that music interventions in the perioperative period can effectively reduce postoperative vomiting, although the impact of music therapy and interventions on nausea remains unclear. Cannabinoids have also been used for treatment of PONV, but its safety and efficacy are controversial. ==Epidemiology==

Typically, the incidence of nausea or vomiting after general anesthesia ranges between 25 and 30%. Nausea and vomiting can be extremely distressing for patients, and so is 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 PONV. ==References==