Post-operative nausea and vomiting is one of the most common complaints adults have after undergoing anesthesia for a surgical procedure. Children, though, have an even higher incidence of post-op vomiting.1 They also have nausea more often, but because nausea is difficult to diagnose in these patients, it's most likely underreported. In both cases, our focus is on doing all we can to alleviate these unpleasant adverse effects.

We got help in 2003 when some of the best known experts in our field developed the "Consensus Guidelines for the Management of PONV," an evidence-based tool to help clinicians prevent these problems. In October, a multidisciplinary panel made further modifications, with a greater emphasis on preventing and treating PONV in children. Here, we'll highlight some of the key parts of these guidelines.

Criteria for candidates
Prophylactic management of pediatric PONV typically requires using drugs that may be expensive or are associated with unwanted side effects.2 Since it isn't feasible or effective to give the drugs to everyone, it's best to target those children at particular risk as candidates for this treatment.

The risk factors for children are similar to those for adults, but there are a few notable differences. PONV is rare when the patient is younger than 2, but it increases with age until puberty, after which it tapers. A recent study in children younger than 14 years old noted a sharp increase in PONV at age 3, with a 0.2 percent to 0.8 percent per year increase in risk thereafter.3 There appears to be no gender difference among pre-adolescent patients and a history of PONV or motion sickness in a child's parent or sibling may be a factor. Certain surgical procedures are also associated with a higher incidence in children, including adenotonsillectomy, strabismus repair, orchidopexy, penile surgery and hernia repair.4

The revised consensus guidelines included a simplified risk score to determine the degree of risk in children. This was based on the number of the following risk factors that are present:

• duration of surgery ? 30 minutes;
• age ? 3 years;
• strabismus surgery; and
• history of PONV or PONV among relatives.

The risk of PONV is elevated as the number of risk factors increases, with one risk factor representing a 10 percent risk and four risk factors representing a 70 percent risk.

Straightening the baseline
Having determined the patients who are at risk for PONV, the next step is to address factors for reducing baseline risks. In adults, this usually means eschewing nitrous oxide and volatile anesthetic agents to favor the use of propofol for total IV anesthesia, but this has yet to be validated in pediatrics. In adults, the avoidance of general anesthesia by the use of regional techniques is recommended in patients with a high risk for PONV. Although regional anesthesia doesn't always apply to children, its use to minimize opiate requirements may reduce the incidence of pediatric PONV.5 It's also important to add that the new consensus guidelines no longer recommend the use of supplemental oxygen and hydration to reduce baseline risks for PONV.

Prophylactic drug therapies can either be monotherapy or a combination of medications. The prophylactic antiemetics recommended for pediatric patients include the 5-HT3 antagonists ondansetron, dolasetron, granisetron and tropisetron. After the first guidelines were published, ondansetron (0.05 to 0.1mg/kg up to 4mg) received approval for use in children as young as one month of age and granisetron (40mg/kg) and tropisetron (0.1mg/kg) were added as therapeutic options. Because the

5-HT3 antagonists as a group have greater efficacy in the prevention of vomiting than nausea, these are the first-line choices for prophylaxis in children.

Other therapies include dexamethasone (0.15mg/kg), droperidol (0.05 to 0.075mg/kg up to 1.25mg), dimendydrinate (0.5mg/kg) and perphenazine (0.07mg/kg). The revised guidelines specify an upper limit for the dose range of dexamethasone, reduced from 8mg to 5mg, to address concerns over unwanted side effects. The guidelines also recommend that children who are at moderate or high risk for PONV should receive combination therapy with two or three prophylactic drugs from different classes (in contrast, the recommendations for adults suggest that combination therapy should be reserved for "high-risk" patients only). The recommended combinations are:

• ondansetron (0.05mg/kg) with dexamethasone (0.15mg/kg)
• ondansetron (0.1mg/kg) and droperidol (0.15mg/kg) or
• tropisetron (0.1mg/kg) and dexamethasone (0.5mg/kg).

When prevention fails
To treat PONV when it occurs or when prophylaxis fails, choose an antiemetic from a different therapeutic class than the agents you used for prophylaxis. You can use droperidol for pediatric patients who have failed all other therapies and are being admitted to the hospital, but you should be aware of the potential for extrapyramidal side effects. Also, the "black box" warning on droperidol issued by the FDA in 2001 may significantly reduce its availability and make some physicians unwilling to use it.

If everything else fails, it may be time to consider some of the non-pharmacological therapies that have been studied in pediatric patients. For example, acupuncture has been successfully used to prevent PONV in children undergoing strabismus repair, dental surgery and tonsillectomy.6

Just for kids
As is often the case in medicine, it's tempting to manage children based on evidence obtained from adult data. But the pediatric population is difficult to study because of its diversity, as evidenced by the differences between neonates and adolescents, and is further complicated by poor communication skills, and consensual and ethical issues. The aim of the revised consensus guidelines for the management of PONV is to review all available data for clinicians to make evidence-based clinical decisions. And since the incidence of PONV is undoubtedly higher in children than in adults, there is a great need for better understanding and age-appropriate management for our younger patients.

References:
1. Lerman J. Surgical and patient factors involved in postoperative nausea and vomiting. Br J Anaesth. 1992;69(7 Suppl 1):24S-32S.
2. Gan TJ. Risk factors for postoperative nausea and vomiting. Anesth Analg. Jun 2006;102(6):1884-1898.
3. Eberhart LH, Geldner G, Kranke P, et al. The development and validation of a risk score to predict the probability of postoperative vomiting in pediatric patients. Anesth Analg. Dec 2004;99(6):1630-1637, table of contents.
4. Gan TJ. Postoperative nausea and vomiting-can it be eliminated? JAMA. Mar 13 2002;287(10):1233-1236.
5. Khalil SN, Farag A, Hanna E, Govindaraj R, Chuang AZ. Regional analgesia combined with avoidance of narcotics may reduce the incidence of postoperative vomiting in children. Middle East J Anesthesiol. Feb 2005;18(1):123-132.
6. Habib AS, Gan TJ. Evidence-based management of postoperative nausea and vomiting: a review. Can J Anaesth. Apr 2004;51(4):326-341.