Being A challenging complaint, many studies tried to find an effective preventive strategies for PONV. In this study protocol the investigators aim to compare between 0.5 mic/kg and 0.75 mic/kg bolus doses of dexmedetomidine when given toward the end of head and neck surgeries in highly susceptible patients with a controlled group receiving ondansetron.~The primary outcome is the 1st 24 hours incidence of PONV~Other outcomes include:~Time to 1st call for rescue antiemetic and the total amount of antiemetics~Number of PONV attacks~Post operative pain score with visual analogous scale (VAS) and time to 1st call for rescue analgesia~Sedation Score using Observer's Assessment of Alertness and sedation (OAA/S)~Patient satisfaction~Vital signs in the 1st 24 hours
The study aims to compare between two bolus doses of dexmedetomidine in preventing PONV in highly susceptible patients.