Aprepitant, a selective antagonist of neurokinin-1 (NK-1) receptors, blocks the emetic effects of substance P. NK-1 receptors are found on vagal afferents in the gastrointestinal tract and in the nucleus tractus solitaries in the brain. Substance P action on the NK-1 receptors in the central nervous system (CNS) is one of the final pathways to an emetic response.
Scopolamine antagonizes muscarinic type 1 (M1) and histamine type 1 (H1) receptors in the CNS, hypothalamus, and vomiting center. The noradrenergic system is also suppressed resulting in a diminished response to vestibular stimulation. Surgical procedures, opioids, and movement postoperatively all stimulate the vestibular system making scopolamine effective prophylaxis for PONV.
In adults undergoing general anesthesia with inhalational anesthetic agents, predictive risk factors for PONV include female sex, history of PONV or motion sickness, nonsmoking status, and the use of postoperative opioids. The frequency of PONV is 10% with zero, 21% with one, 39% with two, 61% with three, and 79% with 4 risk factors. The type of surgery also plays a major role. High risk procedures include intrabdominal, laparoscopic, orthopedic, major gynecologic, thyroid, otolaryngological, neurosurgical, breast, and plastic surgery.
Improving PONV prophylaxis would have a profound impact on patient care. Decreasing the incidence of nausea, vomiting, need for rescue medication, prolonged PACU time, and unplanned admissions is beneficial. Recent evidence suggests multiple drug therapy is superior to single agents. The correct preoperative treatment medication is instrumental in the outcome. This study compares the incidence of nausea, vomiting, need for rescue medication, prolonged PACU time, and unplanned hospital admission in patients with high risk for PONV treated with oral aprepitant with or without transdermal scopolamine preoperatively.
