Postoperative nausea and vomiting is the phenomenon of nausea, vomiting or retching experienced by a patient in the Post Anesthesia Care Unit or within 24 hours following a surgical procedure. It is an unpleasant complication that affects about 10% of the population undergoing general anaesthesia each year.
Cause
Emetogenic drugs commonly used in anaesthesia include nitrous oxide, physostigmine and opioids. The intravenous anaestheticpropofol 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. This makes it incredibly sensitive to toxin and pharmacological stimulation. There are multiple neurotransmitters such as histamine, dopamine, serotonin, acetylcholine, and the more recently discovered neurokinin-1.
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 post-operative 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. Postoperative nausea and vomiting results from patient factors, surgical & anesthetic factors. Surgical factors that confer increased risk for PONV include procedures of increased length, gynecological, abdominal and laparoscopic procedures, ENT procedures, strabismus procedures in children. Anesthetic risk factors include the use of volatile anesthetics, Nitrous Oxide, 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 pre-operative anxiety and patients with history of PONV in the past. Smokers and the elderly often have a decreased risk for PONV. A risk-stratification method created by Apfel et all has been developed to determine a patient's risk for PONV. The presence 0, 1, 2, 3, and 4 of any of the following risk factors corresponds to a PONV respective risk of 10, 20, 40, 60, and 80 percent. - Female Gender - Non-smoking - History of PONV or motion sickness - Expectant use of post-operative Opioid medications
Management
Because there is currently no single antiemetic available is especially effective on its own, experts recommend a multimodal approach. Anesthetic strategies to prevent vomiting include using regional anesthesia whenever possible and avoiding medications that cause vomiting. Medications to treat and prevent postoperative nausea and vomiting are limited by both cost and the adverse effects. People with risk factors likely warrant preventative medication, whereas a "wait and see" strategy is appropriate for those without risk factors.
Preoperative fasting
Fasting guidelines often restrict the intake of any oral fluid after two to six hours preoperatively. However, it has been demonstrated in a large retrospective analysis in Torbay Hospital that unrestricted clear oral fluids right up until transfer to theatre could significantly reduce the incidence of postoperative nausea and vomiting without an increased risk in the adverse outcomes for which such conservative guidance exists.
Medications
A multimodal approach to treating a patient with PONV can be efficacious. Numerous patient factors as well as medication adverse effects must be taken into consideration when selecting a treatment regimen. Serotonin Receptor Antagonists- Can be administered as a single dose at the end of surgery. Adverse effects include prolongation of the QT interval on EKG. - Medications include ondansetron, granisetron, dolasetron Anticholinergics- Can be used as a long-acting patch placed behind the patient's ear. Adverse effects include dry mouth, 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 effect and can reduce need for post-op opioids. Adverse effects include transient increase in serum glucose level, and poor wound healing - Medications include: dexamethasone Butyrophenones: Typically administered as a single injection at the end of surgery. Adverse effects include prolongation of the QT interval on EKG. - Medications include: droperidol, haloperidol Phenothiazines: Particularly effective in treating opioid-induced PONV. Adverse effects are dose-dependent and include sedation and extrapyramidal symptoms. - Medications include: Promethazine, Prochlorperazine Neurokinin 1 Receptor Antagonists: - Medications include: Aprepitant, Rolapitant Histamine Receptor Antagonists: Can be administered via multiple routes including orally, IM or rectal. Adverse effects include dry mouth, sedation, urinary retention. - Medications include: Dimenhydrinate, Diphenhydramine Propofol: an anesthetic medication that confers antiemetic properties
Alternative medicine
In conjunction with antiemetic medications, at least one study has found that application to the Pericardium Meridian 6 acupressure point produced a positive effect in relieving postoperative nausea and vomiting. 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 that there is no significant difference between the use of either therapy in the treatment or prevention of PONV. In a review of 59 studies it was found that both therapies significantly affected the nausea aspect, but had no significant effect on vomiting. Cannabinoids have also been used for treatment of PONV however its efficacy is controversial.
Epidemiology
On average the incidence of nausea or vomiting after general anesthesia ranges between 25 and 30% . Nausea and vomiting can be extremely distressing for patients and is therefore 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 postoperative nausea and vomiting.
