Collapsed lung is one of the important problems in critically ill patients, and the clinical condition may worsen rapidly. Treatment with a therapeutic fiberoptic bronchoscopic procedure at the bedside was introduced and good results were reported in many studies. This therapeutic procedure includes repetitive sputum suctioning and bronchial washing with normal saline solution; complete or partial re-expansion of atelectasis was attained in 60 to 90 percent of the cases.
When the lung volume decreases, the alveolar radius will decrease and the alveolar pressure rise according to Laplace relationship: Рт = 2 T/r (Рт-alveolar pressure, T-alveolar surface tension, r-alveolar radius). In these conditions, the surfactant will work to lower the alveolar surface tension; this reduction in surface tension offsets the reduction in alveolar radius and prevents alveolar pressure from rising. But if the atelectasis is profound, the reduction in surface tension can not overcome the reduction in alveolar radius, and the alveolar pressure will rise and create a higher critical opening pressure in the atelectatic alveoli and lower lung compliance. The above findings are especially common in cases with a small area of collapse. In these cases, the transpulmonary pressure of the atelectatic alveoli is often too low to overcome the critical pressure. These refractory atelectasis do not easily re-expand even after the above bronchoscopic procedures. It would be useful if we could introduce positive pressure ventilation directly into the collapsed area to overcome the critical opening pressure. But if we can not sufflate the air directly into the atelectatic alveoli, the insufflated air will tend to be distributed into the noncollapsed areas because of lower airway resistance and higher lung compliance. This will result in a hyperinflated normal lung area which in turn will compress the collapsed area.