Answer is A (Iatrogenic Pneumothorax): Subclan vein cannulation is an impoant cause of iatrogenic pneumothorax. Absence of breath sounds and Hyper-resonance of chest wall on percussion alongwith sudden breathlessness after attempted subclan vein cannulation suggests a diagnosis of Iatrogenic Pneumothorax. Common causes of Iatrogenic Pneumothorax (Decreasing order of frequency) Transthoracic Needle Lung Biopsy Subclan vein cannulation Thoracocentesis Pleural Biopsy Positive Pressure ventilation Iatrogenic Pneumothorax History History of Procedure known to cause iatrogenic pneumothorax (subclan vein cannulation) Sudden onset Breathlessness Chest discomfo / chest pain Examination Inspection/ palpatum * Reduced movements over affected side * Mediastinal shift to opposite side * Decreased vocal fremitus Percussion Hyper-resonant Auscultation Diminished or absent breath sound