Diaphragmatic Dysfunction and Cardiac Surgery; Perioperative Assessment and Effect on Outcome

Inclusion Criteria: * 18 years old and older * Planned cardiac surgery * Ready for weaning from mechanical ventilation (fraction of inspired oxygen (FIO2) ≤ 50%, positive end-expiratory pressure(PEEP) level≤ 5 centimeter water (cmH2O), respiratory rate ≤30 breaths/min, partial pressure of oxygen in arterial blood(PaO2)/FIO2 ratio \>200 , Glasgow coma score ≥14). * Stable cardiovascular status (i.e., heart rate \<120 beats/min; systolic blood pressure, 90-160 mmHg; and no or minimal vasopressor use, i.e., dopamine or dobutamine ≤5 μg/kg/min or noradrenaline ≤0.05 μg/kg/min). * Stable metabolic status (i.e., electrolytes and glycaemia within normal range, body temperature \<38 °C, hemoglobinemia ≥8-10 g/dL). Exclusion Criteria: * Patients with a history of diaphragmatic or neuromuscular disease or evidence of pneumothorax or pneumomediastinum. * Patients with low EF (EF ≤ 30%). * Patients with post-operative cerebrovascular stroke. * Reventilation due to cardiac cause ( arrest, arrhythmias, or failure) * Patient refusal.