A pneumothorax is air in the pleural space. It may be spontaneous or related to trauma.
Clinical signs of a pneumothorax are reduced breath sounds/air entry on auscultation and being hyper-resonant to percussion. There may also be mediastinal shift if the pneumothorax is large enough. This can be detected by feeling for the trachea in the neck and determining if it is midline or not.
A big tension pneumothorax is a medical emergency. A large bore needle to aspirate the air must be inserted quickly to save the patient's life. This can be done by grabbing a large bore cannula (18 gauge or larger) and poking in the second intercostal rib space in the mid-clavicular line.
A tension pneumothorax should NEVER be confirmed by X-ray. If it is not obvious clinically, the patient is likely to be dead by the time the X-ray is taken.