Study will be conducted in Pediatric Intensive Care Unit (PICU) in King Abdullah Specialist Children Hospital (KASCH), National Guard Health Affairs, Riyadh, Saudi Arabia. Total of 430 patients will participate to assess the safety and efficacy of prolonged Dexmedetomidine use beyond 24 hours in pediatric Intensive Care Unite.

Prospective, randomized, open label, controlled study, will be conducted in Pediatric Intensive Care Unit (PICU) in King Abdullah Specialist Children Hospital (KASCH), National Guard Health Affairs, Riyadh, Saudi Arabia. 340 patients will be randomly randomized to Midazolam (M) or Dexmedetomidine (D), to assess the safety and efficacy of prolonged Dexmedetomidine use beyond 24 hours.

Inclusion Criteria:

1. Age 1-14 years both male and female who require mechanical ventilation
2. Informed consent from signed by patient's legal representatives, and for patients aged 12- 14 who has an age-appropriate understanding additional assent form signed by patient is required.
3. Intubated within 6 hours and anticipated to require mechanical ventilation for more than 48 hours

Exclusion Criteria:

1. Septic shock and/or multi-organ failure.
2. Hemodynamically instability and requires inotropes.
3. Severe intracranial or spinal trauma with high intracranial pressure
4. Liver failure
5. Acute or chronic renal failure.
6. Glasgow Coma Scale (GCS) ≤8
7. Known to have allergy to the study drugs
8. Airway surgery