Pneumothorax and tension pneumothorax

A pneumothorax is air in the pleural space that has broken the negative pressure holding the lung out against the chest wall, so the lung on that side collapses away from it and stops taking part in gas exchange -- the air entering through a wound in the chest wall, through lung punctured from inside by a fractured rib, a central venous catheter, a thoracentesis or a biopsy needle, through a bleb that has burst in the previously well patient of tall slim build or in lung already diseased by emphysema, asthma or infection, or through alveoli forced open by positive-pressure ventilation -- and it declares itself on one side as sudden pleuritic chest pain and breathlessness with a climbing respiratory rate and pulse, reduced movement of that side of the chest, breath sounds that are diminished or absent over it, a hyperresonant percussion note, a falling saturation and a patient who is restless and anxious; the danger that makes it an emergency is that the leak can behave as a one-way valve, admitting air on every breath and letting none out, so pressure builds in the pleural space until it flattens the lung completely, pushes the mediastinum towards the opposite side and kinks the great veins so the heart can no longer fill -- a breathing problem that has become obstructive shock and can end in cardiac arrest within minutes -- and that tension is recognised at the bedside by respiratory distress that is severe and worsening with absent breath sounds and a hyperresonant hemithorax on one side, a falling blood pressure with a rising heart rate, distended neck veins, cyanosis and agitation, and in the patient on positive-pressure ventilation by airway pressures that suddenly climb while the saturation and blood pressure fall, with tracheal deviation away from the affected side and absent movement of that hemithorax being late signs that are never waited for; so the nurse who suspects tension treats it as the one respiratory emergency in which sending the patient for imaging is itself the fatal act -- staying with the patient and sending someone else for the emergency team rather than leaving to fetch help, giving high-concentration oxygen, sitting the patient upright if the blood pressure allows it, starting continuous monitoring of rate, rhythm, blood pressure and saturation, securing intravenous access, and preparing at once for needle decompression of the affected side followed by a chest drain, because the decompression is a clinical decision acted on before any film is seen, while an open sucking chest wound is covered with a dressing sealed on three sides so that air can leave the chest but cannot be drawn in; and a pneumothorax that is small and a patient who is stable may instead be observed or aspirated, but only with the same watch kept for the enlargement that turns it into the emergency, because the patient most likely to tension is the one everybody has decided is stable.