What are the treatment options available for PONV?
There are several medications that are commonly admin-istered either prophylactically or as direct treat-ment. The following five drugs will be reviewed: droperi-dol, 5-HT3 antagonists, metoclopramide, scopolamine, and dexamethasone.
· Droperidol is a pharmacologic relative of the more widely used antipsychotic drug haloperidol. It is a potent α-adrenergic antagonist. Historically, it was combined with fentanyl and used in neuroleptic anesthesia. In smaller doses, ranging from 0.25 to 2.5 mg given intravenously, it significantly decreases the incidence of PONV. When given in higher doses, it may be associated with excessive sedation and delay in discharge from the PACU. A new controversial US Food and Drug Administration (FDA) “black box” warning notes that droperidol can cause QT prolongation, has been associated with precipitating lethal arrhythmias (e.g., torsades de pointe), and should not be administered in the presence of known QT pro-longation. Further, in the absence of a prolonged QT interval, patients who receive droperidol should have elec-trocardiogram (ECG) monitoring for 3 hours afterwards.
· Ondansetron, dolasetron, and granisetron are the only 5-HT3 antagonists currently FDA-approved for PONV. There does not seem to be any significant difference in efficacy between these two drugs. These medications are devoid of the side-effects of the other medications, but their cost is much higher. The optimal dose of ondansetron is 4 mg intravenously, but the optimal tim-ing of administration seems unclear, with the most recent manufacturer’s recommendation being that it should be administered at the time of induction. The dose of dolasetron is 12.5 mg intravenously, with the time of administration reportedly not critical. Conflicting evidence has been published regarding the efficacy of 5-HT3 antagonists versus older agents, such as droperidol. In the best of cases, a minimal benefit is seen with 5-HT3 antagonists.
· Metoclopramide is a methoxychlorinated derivative of procainamide and is a dopamine antagonist. The antiemetic effect results from its ability to increase acid clearance, esophageal peristaltic amplitude, lower esophageal sphincter pressure, gastric emptying, and gastric contraction rate and amplitude. It may be admin-istered orally, intramuscularly and intravenously in doses of 10–20 mg. The most problematic side-effects are extrapyramidal reactions. Metoclopramide should not be used in epileptics or in patients taking other medica-tions likely to cause extrapyramidal reactions.
· Scopolamine is an anticholinergic drug that is usually administered as a premedicant. A transdermal prepara-tion that has been widely used to prevent motion sick-ness has been shown in small studies to reduce PONV without significant side-effects. Scopolamine, when administered intramuscularly or intravenously, may cause central cholinergic syndrome, which consists of sedation, amnesia, and euphoria.
· Dexamethasone has been found to be as effective as ondansetron in the prevention of PONV in gynecologic surgery. Most corticosteroids have antiemetic properties through a poorly understood mechanism. A dose of 2.5 mg is sufficient and appears to be free of side-effects. Moreover, dexamethasone is inexpensive. However, its effectiveness in treating established PONV has not been studied.
Non-pharmacologic therapies that have been shown to be effective include:
· Administration of supplemental oxygen (FiO2 >0.3), even if limited to the intraoperative period. This may be the result of decreased nitrous oxide administration. There are studies suggesting that an intraoperative FiO2 of 0.8 might be as effective as ondansetron in preventing PONV in patients undergoing laparoscopic gynecologic surgery.
· Aggressive intravenous rehydration.
· Transcutaneous acupoint electrical stimulation.
· Combining available therapies in a “multimodal” man-agement of PONV has been shown to be highly effective, with vomiting rates of 0, versus 7% with ondansetron alone and 22% with placebo.
There is little difference in outcome or patient satisfac-tion (97% vs. 93%) between patients receiving prophylaxis and those being treated as needed in the PACU, suggesting that prophylaxis might be warranted only in high-risk patients.
Although gastric suctioning prior to the completion of the procedure will empty the stomach and theoretically reduce the incidence of nausea and vomiting, no published evidence has documented its efficacy.