The exclusion criteria included trauma patients, patients with neuromuscular disorders, requiring emergency intubation within 1 hours of arrival, initiated on NIV after extubation and pregnant patients. 

The initiation of NIV in ED is at the treating physician’s discretion. The NIV is delivered to the patient through a fitted face mask on either Continuous Positive Airway Pressure (CPAP) or Bilevel Positive Pressure Ventilation mode (BIPAP) to relieve dyspnea. Parameters are gradually titrated based on patients’ tolerance. The selection of the face mask size is based on the patient’s facial type. The straps of the mask will be fitted properly while remaining comfortable to the patient. 

Patients are placed in a semirecumbent position to avoid aspiration, assuming there is no contraindication to this position. Common indications to initiate on NIV in acute hypoxemic respiratory failure are clinical presentation of respiratory distress at rest (such as active contraction of the accessory inspiratory muscles or paradoxical abdominal motion), or PaO2 less than 60 mmHg at room air or PaO2/FiO2 less than 300 mmHg with supplemental oxygen. The Positive End Expiratory Pressure is usually maintained between 4 and 10 cm H2O. Inspiratory pressure is usually between 10 and 20 cm H2O. The fractional concentration of oxygen is set to achieve peripheral oxygen saturation targets greater than 92%. In addition, appropriate strategies are used to improve NIV tolerance, such as controlling leakage, keeping the anchoring system as comfortable as possible, providing adequate humidification, and administering sedation. Ventilation settings and continuous oximeter parameters will be monitored by attending physicians. 

If the respiratory distress is relieved and oxygenation improved, NIV will be used intermittently or completely liberated. If respiratory failure progressively deteriorates, intubation for invasive mechanical ventilation is performed. However, the decision to intubate is at the discretion of the attending physician. The need for intubation or cardiac arrest is defined as NIV failure.

We will collect baseline data, vital signs, and arterial blood gas (ABG) on arrival to the ED. Baseline data included age, gender, reason for NIV initiation, underlying disease, severity of disease (assessed by sequential organ failure assessment [SOFA] score), presence of septic shock, and presence of ARDS. The baseline data will be collected by the investigator from the case record. The vital signs included heart rate, respiratory rate, systolic blood pressure, diastolic blood pressure, and consciousness (Glasgow Coma Scale). An updated HACOR score will be calculated at NIV initiation in ED (T0) and 1(T1) hours later on NIV. Similarly, the lung ultrasound score and diaphragm exertion score will be calculated. The studies showed patients with updated HACOR scores of lessthan or equal to 7, 7.5–10.5, 11–14, and morethan 14, respectively, were classified as having a low, moderate, high, and very high probability of NIV failure. The primary outcome is NIV failure during 24 hours with follow-up. NIV failure was defined as the requirement of intubation or cardiac arrest after NIV. The NIV failure will be calculated during a 1 hour, 6-hour period, 12 hour, and 24 hour

The lung ultrasound scan is performed using a linear probe (4.2-13MHz). The lung ultrasound score consists of scanning a predetermined 12 zones (6 regions on each hemithorax) of the lung. Lung aeration of each region is graded between 0 to 3 depending on the ultrasound pattern visualized. In each region, points are allocated according to the following ultrasound pattern: normal = 0, well-defined B-lines = 1, coalescent B-lines = 2, and consolidation = 3. The total score for the LUS assessment therefore, ranges from 0 to 36.

The total lung ultrasound score of more than 18 is calculated as a value of high, and less than 18 as low probability for the lung ultrasound component of the Sono u-HACOR score.

Diaphragm Excursion Score measured -Patient with score  less than 1.2 is considered high risk, and more than 1.2 is considered low risk for NIV failure