After obtaining Institutional Ethical Committee approval of Faculty of Medicine, Minia University and written informed consent from patients or first- degree relatives, this prospective randomized non-blind comparative study will be conducted in adult intensive care unit (ICU) of Anesthesia, Intensive Care and Pain management department Minia university hospital over a period from September 2025 to April 2026. This study is designed to compare the effectiveness of two protocols of sequential use of High Flow Nasal Cannula (HFNC) and noninvasive ventilation (NIV) versus NIV alone in patients with Acute Respiratory failure (ARF) admitted to the intensive care unit (ICU). The study will include 75 patients of both sexes, classified as ASA class Ⅰ-ⅠⅠⅠ, divided into three groups with 25 patients in each group.