MSU-
APRV is a different animal altogether. Your P-low is analogous to your "PEEP"- usually 0-5 in APRV. The P-high (35mmHg) is analogous to "CPAP"-the inflation pressure if you will. The danger of pneumo is in higher PEEP because of higher Mean Airway pressures that the chest wall has to work against. (Picture sitting on a super inflated balloon that is laying against sidewalk where the balloon is your lung and the sidewalk+butt=chest wall.) APRV is used to accomodate the decreased compliance of diseased lungs. It is also relatively new to the scene and I believe you will find it used with more frequency in facilities that both have the capability to do it (Newer vents), and practitioners that are comfortable with using new ideas.
And just to make clear- if you truly used 35mmHg of PEEP, the next sound you would hear would be your high pressure alarms followed rapidly by the patients lungs popping.
http://www.aacn.org/pdfLibra.NSF/Fil...e/ci120205.pdf
The above link is to an AACN article that explains APRV far better than I can.
Vandy-
As for multiple chest tubes, I would assume you are asking why more than one would be needed on one side. I'll use a common example-Lets say you have a patient that is post thoracotomy for a wedge resection. The surgeon has created a pneumo and modified the lung anatomy as well. s/he might place one chest tube aimed at the anterior superior apex of the pleural space(where air should accumulate in a slightly inclined supine patient.) and also decide to place another aimed more posterior/inferior (where blood/fluid is more likely to accumulate in a patient.)