high flow nasal cannula (HFNC) oxygen therapy utilizes an air oxygen blend allowing from 21 % to 1 00% FiO2 delivery and generates up to 60 L/min flow rates The gas is heated and humidified through an active heated humidifier and delivered via a single limb heated inspiratory circuit (to avoid heat loss and condensation) to the patient through a large diameter nasal cannula Theoretically, HFNC offers significant advantages in oxygenation and ventilation over COT. Constant high flow oxygen delivery provides steady FiO2 and decreases oxygen dilution. It also washes out physiologic dead space and generates positive end expiration pressure (PEEP) that augments ventilation The heated humidification facilitates secretion clearance, decreases bronchospasm, and maintains mucosal integrity.

This study aims to evaluate the effectiveness of HFNC compared to NIMV in management of Acute hypoxemic and acute hypercapneic respiratory failure

• Acute respiratory failure (ARF) is a common and serious complication among hospitalized patients. It is the most frequent reason for admission to the intensive care unit (ICU) . It carries an in-hospital mortality rate of 20.6% and cost 54.3 billion dollars nationwide in United States in 2009. Among those patients with ARF, 42.1 % of patients require mechanical ventilation (MV), which is associated with a significant increase in both length of stay and medical expense
• ARF can be categorized into acute hypoxemic respiratory failure(AHRF) and acute hypercapneic respiratory failure.
• Supplemental oxygen and treatment of the underlying cause is the mainstay of therapy for AHRF. Options for oxygen therapy include conventional oxygen therapy delivered via nasal cannulae (NC) or face masks (FM) initially, followed by non-invasive ventilation (NIV), and finally intubation or mechanical ventilation (MV) .
• Traditional NC and FM (collectively referred to as conventional oxygen therapy or COT) can achieve flow rates of up to 1 5 L/min. However, these flow rates may be significantly lower than patients' spontaneous inspiratory flow rates and the oxygen is diluted as it is mixed with room air Consequently, the fraction of inspired oxygen (FiO2) delivered Is variable and this is thought to explain why many patients require an escalation of oxygen therapy to NIV or MV.
• By contrast, humidified high flow nasal cannula (HFNC) oxygen therapy utilizes an air oxygen blend allowing from 21 % to 1 00% FiO2 delivery and generates up to 60 L/min flow rates The gas is heated and humidified through an active heated humidifier and delivered via a single limb heated inspiratory circuit (to avoid heat loss and condensation) to the patient through a large diameter nasal cannula Theoretically, HFNC offers significant advantages in oxygenation and ventilation over COT. Constant high flow oxygen delivery provides steady FiO2 and decreases oxygen dilution. It also washes out physiologic dead space and generates positive end expiration pressure (PEEP) that augments ventilation The heated humidification facilitates secretion clearance, decreases bronchospasm, and maintains mucosal integrity
• HFNC has been well studied in the neonatal and pediatric settings However, in adults, the use of HFNC has Primarily been studied in post-cardiac surgery post-extubation and bronchoscopy patients. However, the utility of HFNC use in adults with AHRF in emergency and general inpatient practice is less clear .Heated and humidified high-flow oxygen through nasal cannula (HFNC) has been developed over the past 2 decades, as an alternative to standard oxygen delivery systems
• . In adults, it has been used to treat hypoxemic respiratory failure, cardiogenic pulmonary edema, postoperatively and postextubation in do-not-intubate patients or during bronchoscopy
• To date, the literature supports the possibility to use HFNC as alternative to non-invasive ventilation (NIV) in some settings, while in others might be even superior . It is also an alternative to standard oxygen as first line therapy in management of patients with acute respiratory failure . NIV is strongly recommended in patients with acute-on-chronic respiratory failure associated with acute respiratory acidosis, the vast majority of whom meet the criteria for Chronic Obstructive Pulmonary Disease (COPD) exacerbation
• Recently, Studies revealed no difference of the 30-day mortality and intubation rate between NIV and HFNC, in severe acute exacerbation of COPD with moderate, hypercapnic, acute respiratory failure. In a retrospective study, that suggeste that HFNC oxygen therapy was beneficial, even in respiratory failure Type 2, resulting in significant improvement of both oxygenation and hypercapnia. another study also indicated that HFNO leads to a flow-dependent reduction in PaCO2 in patients with stable hypercapnic COPD, due to a washout of the respiratory tract and a functional reduction in dead space
• Although cumulative evidence supports that HFNC is effective in patients with hypercapnia, randomized studies to compare HFNC vs. NIV in patients with acute, hypercapnic respiratory failure are missing. so the investigator conducting this prospective, randomized, controlled trial, involving patients admitted to the Emergency Department (ED), to compare the efficacy of HFNC versus NIV in the management of acute hypercapnic respiratory failure.

Inclusion Criteria:

• Age above 18
• Acute hypoxemic respiratory failure. (Participants admitted with acute hypoxemic respiratory with the following criteria:

RR> 25 breath/minute Use of accessory muscles of respiration, paradoxical breathing, thoracoabdominal asynchrony.

Hypoxemia evidenced by PaO2 / FiO2 ratio <300)

• Acute hypercapnic respiratory failure ((Participants admitted with acute hypercapneic respiratory with the following criteria:

pO2 less than 60 mm Hg (hypoxemia). pCO2 greater than 50 mm Hg (hypercapnia) with pH less than 7.35. Signs and symptoms of acute respiratory distress)

Exclusion Criteria:

• Patients with preprocedural or post-procedural settings (ex: surgery, bronchoscope) post- extubation,
• Patients with cancer or transplant patients,
• Patients less than 18 years old
• Patients with Heart failure patients
• Patients with renal failure patients
• Patients with hemodynamic instability
• Patients with central causes of hypercapnic respiratory failure
• Patients with disturbed conscious level
• Patients who refuse to participate in the study
• Indication for emergency endotracheal intubation
• Tracheotomy or other upper airway disorders
• Active upper gastrointestinal bleeding

Neither the participant , care provider , the investigator nor the outcome assessor will select patients in both groups , see results of other patients till the end of the study or informed by literature opinion in this intervention