Tension pneumothorax is the most common life-threatening manifestation of barotrauma. The likelihood that a pneumothorax will be under tension depends not only on the volume of air in the pleural space but also on compressibility of the ipsilateral lung. When the lung resists collapse, as in ARDS or with gross hyperinflation, a relatively small amount of intrapleural air may produce positive intrapleural pressure. A tension pneumothorax leads to worsening hypoxemia and decreased venous return with hypotension. Hyperresonance and a reduction of breath sounds on the side of the pneumothorax are common, and inflation pressures are increased.
Atelectasis is a common cause of severe hypoxemia that develops during mechanical ventilation.
Left lung atelectasis may result from intubation of the right mainstem bronchus, a problem that also may lead to overdistention of the right lung. A more common cause of atelectasis is mucoid impaction. Because the right lung is more easily suctioned than the left, the latter is more likely to be affected by retained secretions. With atelectasis of an entire lung, breath sounds are diminished or absent on the affected side, with a shift of the trachea to that side. A chest radiograph will reveal increased opacity in the affected hemithorax, together with ipsilateral tracheal shift and elevation of the hemidiaphragm.