Diaphragmatic Ultrasound With Theophylline Therapeutic Trials

All patients will be subjected to: 1. medical history. 2. clinical examination. 3. diaphragmatic ultrasound : diaphragmatic thickness and excursion will be assessed. 4. theophyllin treatment; 200 mg/d orally for 12 days then reassessment of diaphragm by ultrasound. 5. weaning trial ; Patients are considered ready for weaning when they meet all the following criteria: fraction of inspired oxygen (FiO2) \< 0.5, positive end expiratory pressure (PEEP) ≤ 5 cm water , Pa O2/Fi O2\> 200, respiratory rate (RR) \<30 breaths/min, alert and cooperative, and hemodynamically stable in the absence of any vasopressor therapy support.(11) 1. rapid shallow breathing index (RSBI) will be measured. It's defined as the ratio between the respiratory rate (breaths/min) and tidal volume (TV) (liters). 2. 2-hour spontaneous breathing trial with a T-piece and zero pressure support (before extubation). 3. extubation is done \& follow up for 48 hours

Inclusion Criteria: * The inclusion criteria are as follows: critical ill patients that are admitted to our ICU whether they are mechanically ventilated or not . Exclusion Criteria: * exclusion criteria are the presence of pneumothorax or ascites, a history of either neuromuscular disease or thoracic surgery, congenital diaphragmatic hernia, the presence of a tracheostomy tube,chronic obstructive pulmonary disease (COPD) patients, asthma and poor image quality.