POSITION MAY STOP PNEUMOTHORAX PROGRESSION IN DOGS

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Abstract
To determine the effect of position on the rate of pneumothorax formation, 6 anesthetized, spontaneously breathing dogs in the left decubitus position had a chest tube 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 avacuated 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. This maneuver caused the site of leak to completely seal 11 of 21 times in which the puncture site was placed dependent. There was no significant change in the rate of pneumothorax formation with the puncture site kept in the nondependent position. Apparently, placing the site of pleural gas leak in the most dependent position causes a reduction in alveolar size and the alveolar to pleural pressure gradient in the region surrounding the leak. Both of these factors would tend to slow the rate of penumothorax formation and allow sealing of the puncture site.