Adults with ARF and within 8 h of starting NIV were randomized to receive IV dexmedetomidine ( 0.2 g/kg/h titrated every 30 min to 0.7 g/kg/h to maintain a Sedation-Agitation Scale [ SAS ] score of 3 to 4 ) or placebo in a double-blind fashion up to 72 h , until NIV was stopped for 2 h , or until intubation .