A 70-yeаr-оld with chrоnic systоlic heаrt fаilure presents with acute respiratory distress. Findings: RR 36/min, SpO₂ 80% on room air, BP 170/94, crackles to mid-lung fields, pink frothy sputum, S3 present. The client is anxious and speaking in single words. What is the nurse’s priority action?