TY - CHAP M1 - Book, Section TI - Airway Pressure Release Ventilation A1 - Andrews, Penny A1 - Nieman, Gary A1 - Kollisch-Singule, Michaela A1 - Madden, Maria A1 - Habashi, Nader A2 - Farcy, David A. A2 - Chiu, William C. A2 - Marshall, John P. A2 - Osborn, Tiffany M. PY - 2016 T2 - Critical Care Emergency Medicine, 2e AB - For those who have limited exposure to airway pressure release ventilation (APRV), it may help to conceptualize the following discussion through two paradigms. One is to consider high pressure (PHigh) similar to a higher pressure CPAP with periodic releases or breaks. When pressure is held over time, the pressure may dissipate over the lung field. As the pressure dissipates and alveoli begin to open, the wall tension of connected (unrecruited) alveoli is changed, facilitating their recruitment. The time over which the CPAP (PHigh) is held is the “Time high” (THigh). The second paradigm is visualizing blowing up a balloon and holding it by the balloon neck. The PHigh could be considered the pressure within the inflated balloon. PLow is the lower pressure outside the balloon. The Thigh could be considered the amount of time the neck of the balloon is held closed. The TLow could be analogous to how long the neck of the balloon is released. Using the inflated balloon analogy, how much air leaves the balloon (and thus how much remains) is a factor of the pressure differential between the inside of the balloon and the outside, how long the neck of the balloon is released, and extrinsic forces being applied to the outside of the balloon. So, if the neck of an inflated balloon were released for 30 seconds, most of the air would leave the balloon as the pressures equilibrated and the “patient would derecruit.” If the neck of the inflated balloon were to be released for 0.5 seconds, there would be some release of air, but a significant amount would still be retained within the balloon. As will be explained later, this is why there is CO2 release without derecruitment and why the traditional setting of PLow is zero. Further, extrinsic factors can impact how much air is released during a given TLow. For example, as abdominal hypertension progresses to abdominal compartment syndrome, the abdominal contents press against the diaphragm, causing more air to be released during a given TLow, similar to the inflated balloon being compressed while releasing the neck of the balloon. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/03/28 UR - accessemergencymedicine.mhmedical.com/content.aspx?aid=1135699749 ER -