Traditionally, one traumatic and one medical cause is attributed to paradoxical breathing. However, almost any cause of shortness of breath, if severe enough, can lead to paradoxical breathing.
In only one cause, flail chest, is paradoxical breathing a diagnostic sign all by itself.
The most common cause for paradoxical breathing noted in the literature is called a flail chest, which consists of a segment of the free-floating chest wall from multiple rib fractures.
It takes a minimum of four complete rib fractures to develop a flail segment, which is defined as two or more consecutive ribs each broken in two or more places.
Some sources suggest that at least three adjacent ribs must be broken in order to qualify as a flail segment. It’s not as much about the number of ribs involved as it is about the size of the segment.
Flail chest is a very rare condition. In one study of 25,467 trauma patients admitted over a six-year period, only 85 patients had a flail segment, about 1/3 of a percent.
The amount of force needed to cause a single rib fracture is significant. To create a flail segment, that level of force must be applied over a much larger area and break an entire section of ribs apart from its neighboring rib cage.
Such force is likely to damage much more than just the chest wall. Many patients with flail chest also have associated internal injuries.
The movement of the free-floating flail segment is paradoxical because it sucks in when you inhales and bulges out when you exhales. This is the opposite movement of the rest of the chest wall.
The movement of a large flail segment minimizes the efficacy of your attempts to breathe. It’s hard to expand the chest to move air in because the segment moves in and reduces the change in overall chest volume. The same thing happens during exhalation.
In flail chest, paradoxical breathing can lead to complications such as pneumothorax and pneumonia.