Dexmedetomidine Versus Dexmedetomidine With Ketamine in Mechanically Ventilated ARDS Patients

The goal of this clinical trial study is to compare dexmedetomidine versus the combination of dexmedetomidine with ketamine in hemodynamic changes and sedative effects in ARDS patients who are in need of mechanical ventilation. The main question[s] it aims to answer are: - [question 1]: Which dose that get the target in sedation, single and combined drugs? - [question 2]: In which drug group that hemodynamic did not affect Participants will be patients with ARDS that will be divided into two group the first ont will receive dexmedetomidine 0.5 µg/kg/h mixed with ketamine 0.5 mg/kg/h and the second one will receive dexmedetomidine at 0.5 µg/kg/h infusion only. In both the groups, studied drugs will be titrated to achieve target sedation.