RT Book, Section
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.
SR Print(0)
ID 1135699749
T1 Airway Pressure Release Ventilation
T2 Critical Care Emergency Medicine, 2e
YR 2016
FD 2016
PB McGraw-Hill Education
PP New York, NY
SN 9780071838764
LK accessemergencymedicine.mhmedical.com/content.aspx?aid=1135699749
RD 2024/04/23
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.