Impact of Timing of Midazolam Administration on Incidence of Postoperative Nausea and Vomiting

Midazolam is often administered in the perioperative period to reduce anxiety in addition to causing sedation and amnesia. The pharmacologic qualities allow for a rapid onset, short duration, and short half-life. The clinical effects of midazolam result from an agonist action on the γ-aminobutyric acid A (GABAA) receptor throughout the central nervous system. Benzodiazepines do not work directly on the GABA receptor, so there is a physiologic ceiling effect, which contributes to their safety and low toxicity. Although the exact antiemetic mechanisms remain unknown, researchers postulate that midazolam works on the chemoreceptor trigger zone by reducing the synthesis, release, and postsynaptic dopamine. It remains debatable whether midazolam reduces dopamine directly or blocks the reuptake of adenosine leading to an adenosine-mediated reduction of dopamine release. Additionally, the binding of midazolam to the GABA benzodiazepine complex may cause dopaminergic neuronal activity and the release of 5-hydroxytryptamine. The reduction of PONV may also be a secondary effect of the anxiolytic properties of benzodiazepines. Despite literature demonstrating the PONV benefits of midazolam in the perioperative period, But the timing of administration of this drug is still not well established. As it is known that it has half-life of about 1.5 - 2.5 hours and the controversies remain whether to administer this drug preoperatively or postoperatively to prevent PONV. So this comparative study is designed to know the better time for administration of this drug to prevent PONV and to improve patient satisfaction.