Once randomized, patients allocated to the propofol group will be initiated with a 0.5-1 mg/kg i.v. bolus followed by repeated 10-20 mg doses at variable intervals (approximately 15 s, at the discretion of the physician/nurse) until an appropriate level of sedation will be achieved (NICU protocol), which will be subsequently titrated to achieve a target Richmond Agitation-Sedation Scale (+4 = combative to -5 = unarousable) (Sessler et al. The Richmond Agitation-Sedation Scale.Am J Respir Crit Care Med 2002; 166:1338-1344). Nurses will note pre-sedation levels based on the Richmond Agitation-Sedation Scale. While undergoing sedation, target sedation will be defined when the Richmond Agitation-Sedation Scale meets a score of -4 to -5. Patients randomized to the midazolam group will be initiated with 0.5-1.0 mg with incremental dosing at intervals of approximately 1-3 min until a level of sedation will be achieved at a target Richmond Agitation-Sedation scale sedation score (per NICU protocol).