No participants enrolled in study.

The purpose of this study is to learn how 2 medications (fentanyl and dexmedetomidine) affect how sick children think and interact with their environments.

Inclusion Criteria:

• Ages 2-<18 at the time of enrollment
• Admitted to the Duke PICU or PCICU
• Planned or anticipated mechanically ventilation for ≥2 days
• Require sedation to maintain mechanical ventilation
• No contraindication to receipt of fentanyl or dexmedetomidine per clinician judgment
• Availability and willingness of the parent/legal guardian to provide written informed consent

Exclusion Criteria:

• Any concomitant condition, which in the opinion of the investigator would preclude a subject's participation in the study.
• Previous participation in this study
• Planned receipt of sedatives other than fentanyl or dexmedetomidine
• Participants with any of the following diagnoses: traumatic brain injury, intracranial hemorrhage, baseline neurodevelopmental delay, status epilepticus, or requiring inotropic support for hemodynamic stability.
• Renal failure requiring renal replacement therapy
• Hepatic failure
• Support with extracorporeal membrane oxygenation