Role of Ultrasound Assessment of Parasternal Intercostal Muscle Thickness During Weaning From Mechanical Ventilation

Inclusion Criteria: Any patient invasively mechanically ventilated at least 24 hours on a pressure support mode who is clinically stable and ready to undergo a spontaneous breathing trial. All patients will be: * Alert. * Afebrile. * Adequate cough with absence of excessive tracheobronchial secretion. * Fraction of inspired oxygen (FIO2) of \<50%. * PEEP ≤8 cmH2O. * PaO2/FiO2 \> 150. * pH ≥7.35 and ≤7.45. * Respiratory rate (RR) ≤35 breaths/min. * Hemodynamically stable in the absence of vasopressors. * Stable metabolic and endocrinal status. * Euglycemic state. * Adequate mentation (no sedation or stable neurologic patient). Exclusion Criteria: Diaphragmatic paralysis (detected by ultrasonography).Patients\&Methods. 6 * Pregnant women. * Age: \>= 18 years. * Surgical dressings over measurement point which would preclude ultrasound exam. * Underweight patients (Body mass index \<18.5 kg/m2). * Morbidly obese patient (Body mass index ≥ 40 kg/m2). * Primary neuro-muscular diseases. * Central coditions with depressed central respiratory drive (encephalitis, and brainstem haemorrhage/ischaemia). * Repiratory conditions with reduced pulmonary compliance (interstitial lung disease, pulmonary hemorrhage, and diffuse pulmonary infiltrates) or reduced chest wall compliance (kyphoscoliosis). * Cardiac conditions with high risk of weaning induced pulmonary edema (congestive heart failure, cyanotic heart diease, pulmonary hypertension, and ischemic heart diease). * Addict patients. * Patients with psychiatric disease.