title: Accuracy of delivered airway pressure and work of breathing estimation during proportional assist ventilation: a bench study.
abstract: BACKGROUND
  Proportional assist ventilation+ (PAV+) delivers airway pressure (P aw) in proportion to patient effort (P mus) by using the equation of motion of the respiratory system. PAV+ calculates automatically respiratory mechanics (elastance and resistance); the work of breathing (WOB) is estimated by the ventilator. The accuracy of P mus estimation and hence accuracy of the delivered P aw and WOB calculation have not been assessed. This study aimed at assessing the accuracy of delivered P aw and calculated WOB by PAV+ and examining the factors influencing this accuracy.
  
  
  METHODS
  Using an active lung model with different respiratory mechanics, we compared (1) the actual delivered P aw by the ventilator to the theoretical P aw as defined by the equation of motion and (2) the WOB value displayed by the ventilator to the WOB measured from a Campbell diagram.
  
  
  RESULTS
  Irrespective of respiratory mechanics and gain, the ventilator provided a P aw approximately 25 % lower than expected. This underassistance was greatest at the beginning of the inspiration. Intrinsic PEEP (PEEPi), associated with an increase in trigger delay, was a major factor affecting PAV+ accuracy. The absolute value of total WOB displayed by the ventilator was underestimated, but the changes in WOB were accurately detected by the ventilator.
  
  
  CONCLUSIONS
  The assistance provided by PAV+ well follows P mus but with a constant underassistance. This is associated with an underestimation by the ventilator of the WOB. PEEPi can be a major factor contributing to PAV+ inaccuracy. Clinical recommendations should include using a high trigger sensitivity and a careful PEEP titration.
authors.affiliation: Keenan Research Centre and Li Ka Shing Knowledge Institute, St. Michael's Hospital, 30 Bond St, Toronto, ON, M5B 1W8, Canada.|Medical Intensive Care Unit, Hospital of Angers, University of Angers, Angers, France.
authors.forename: Francois
authors.initials: F
authors.lastname: Beloncle
authors.affiliation: Department of Intensive Care Medicine, University Hospital of Heraklion, Crete, Greece.
authors.forename: Evangelia
authors.initials: E
authors.lastname: Akoumianaki
authors.affiliation: Keenan Research Centre and Li Ka Shing Knowledge Institute, St. Michael's Hospital, 30 Bond St, Toronto, ON, M5B 1W8, Canada.|Division of Respiratory Diseases and Tuberculosis, Department of Medicine, Faculty of Medicine Siriraj Hospital, Bangkok, Thailand.
authors.forename: Nuttapol
authors.initials: N
authors.lastname: Rittayamai
authors.affiliation: Institut Supérieur des Sciences de la Santé, Université Hassan 1er, Settat, Morocco.
authors.forename: Aissam
authors.initials: A
authors.lastname: Lyazidi
authors.affiliation: Keenan Research Centre and Li Ka Shing Knowledge Institute, St. Michael's Hospital, 30 Bond St, Toronto, ON, M5B 1W8, Canada. brochardl@smh.ca.|Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, ON, Canada. brochardl@smh.ca.
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard