evaluate the Efficacy of high flow nasal oxygen as a weaning strategy in mechanically ventilated patients with respiratory failure.

Acute respiratory failure is a main cause of IMV and admission to intensive care unit (ICU){1}.

The day of extubation is a critical time during an intensive care unit (ICU) stay because in case of postextubation failure {2},which reach to 25 - 40% from extubated patient associated with VAP and barotrauma, mortality rate and hospital stay will increase , we use Adjuvant oxygen therapy to prevent these undesirable event like COT ,NIV and High-flow nasal cannula (HFNC) which can be used as an initial weaning strategy from IMVdue to its physiologic benefits [3-4].

HFNC devices supply between 30 and 60 L/min of a controlled mixture of actively warmed (32-37 °C) and humidified (up to 100% relative humidity) oxygen and air through modified nasal prongs. producing {5-6-7}:

1. moderate positive end-expiratory pressure (PEEP) .
2. HFNC might help prevent extubation failure through different

Mechanisms:

1. First, the controlled oxygen concentration may reduce transient hypoxemic episodes .
2. Second, the high flow washes the nasopharyngeal dead space, thus reducing CO2 re-breathing; this effect reduces respiratory rate and minute ventilation .
3. Third, the small amount of PEEP may reduce lung collapse . c)enabling better gas exchange and reduced work of breathing. d)in patients with chronic obstructive pulmonary disease (COPD), this level of PEEP may counterbalance auto PEEP, further reducing the work of breathing.

e) humidification may improve mucus drainage and reduce mucus retention, alleviating the associated atelectasis.

Inclusion Criteria:

1- All adult patients who were admitted to our ICU requiring endotracheal intubation (ETI), were eligible for the study.

Exclusion Criteria:

1. Non-intubated patients or those with tracheostomy were excluded from the study.
2. those having neurological alteration unrelated to hypercapnoeic encephalopathy, cranio-facial deformity, upper airway obstruction, cardiogenic pulmonary edema, cardiogenic shock, acute myocardial infarction, pneumothorax, pulmonary neoplasm, pulmonary thromboembolism, gastrointestinal bleeding, and post-operative respiratory failure.
3. Patients less than 18 y.

all patient in respiratory ICU who mechanically intubated will be enrolled in study by using high flow nasal oxygen as a weaning strategy.