Position may stop pneumothorax progression in dogs.

We attempted to see what the effect of position was on the rate of pneumothorax formation. In 6 anesthetized spontaneously breathing dogs in the left decubitus position, a chest tube was inserted into the right hemithorax. A right-sided pneumothorax was induced by percutaneous transthoracic insertion of a 20-gauge needle into the lung. Once a constant rate of pneumothorax formation occurred, the dogs were alternated between 3 min of no evacuation by the chest tube with the puncture site up (left decubitus) or down (right decubitus). The pneumothorax that accumulated was always evacuated immediately thereafter with the chest tube in the highest position (left decubitus). In every case, the rate of pneumothorax formation decreased with the puncture site down rather than with it up. Furthermore, this maneuver caused the site of leak to completely seal 11 of 21 times in which the puncture site was placed dependent. There was, however, no significant change in the rate of pneumothorax formation with the puncture site kept in the nondependent position. These results are consistent with the hypothesis that placing the site of pleural gas leak in the most dependent position causes a reduction in alveolar size as well as the alveolar to pleural pressure gradient in the region surrounding the leak. Both of these factors would tend to slow the rate of pneumothorax formation and allow sealing of the puncture site.