Postoperative nausea and vomiting

Postoperative nausea and vomiting (PONV) is an unpleasant complication affecting about a third of the 10% of the population undergoing general anaesthesia each year.

Cause

Emetogenic drugs commonly used in anaesthesia include nitrous oxide, physostigmine and opioids. The intravenous anaesthetic propofol is currently the least emetogenic general anaesthetic. These medications are thought to stimulate the chemoreceptor trigger zone (CTZ). 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 (substance P).

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.^[1]

Postoperative nausea and vomiting results from patient factors, surgical factors, and anesthetic factors. It has been proven that there is a direct like between length of surgery and risk of postoperative nausea and vomiting (PONV). Due to the length of the procedure, abdominal and laparoscopic are at a higher risk for PONV. Procedures in ENT have an increased risk as well due to the involvement of the vestibulocochlear system. In addition to the length of the surgery the dose of the anesthetic also play a large role in the risk of PONV.

Patients that are female or who have a history of postoperative nausea and vomiting are at greater risk. Smokers have a decreased risk, but this would never be recommended by any physician. Older patients suffer less PONV.

Obesity, age less than 16 years, past history of motion sickness and high levels of pre-operative anxiety are also risk factors for PONV.

Management

Because no currently available antiemetic is especially effective by itself, and successful control is often elusive, experts recommend a multimodal approach. Anaesthetic strategies to prevent vomiting include using regional anaesthesia wherever possible and avoiding medications that cause vomiting. Medications to treat and prevent postoperative nausea and vomiting is limited by both cost and the adverse effects. People with risk factors probably warrant preventative medication, whereas a "wait and see" strategy is appropriate for those without risk factors.

Medications

A Cochrane review found droperidol, metoclopramide, ondansetron, tropisetron, dolasetron, dexamethasone, cyclizine, and granisetron effective for preventing PONV.^[2]

Granisetron and dexamethasone is not recommended due to the higher rate of side effects.^[3]

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.^[4] Another study found no statistically significant difference.^[5] 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.

Epidemiology

On average the incidence of nausea or vomiting after general anesthesia ranges between 25 and 30% [Cohen 1994]. Nausea and vomiting can be extremely distressing for patients and is therefore one of their major concerns [Macario 1999]. 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.

References

<ref>1 Lee, A., Chan, S., Fan, L. (2015). Stimulation of the wrist acupuncture point PC6 for preventing postoperative nausea and vomiting. DOI: 10.1002/14651858.CD003281.pub4 /ref> <ref>Blackburn, J., Spencer, R. (2015). Postoperative nausea and vomiting. /ref> <ref>Pleuvry, B. (2015). Physiology and pharmacology of nausea and vomiting./ref>