title: Tracheal pressure regulated volume assist ventilation in acute respiratory failure.
abstract: OBJECTIVE
  Proportional assist ventilation (PAV) uses volume assist (VAV) and flow assist ventilation (FAV) to reduce elastic and resistive effort, respectively. Proportional assist ventilation may be difficult to apply clinically, particularly due to FAV related considerations. It was hypothesized that regulating tracheal (Ptr) rather than airway opening pressure (Pao), to overcome endotracheal tube related resistive effort, during VAV would provide an effective alternative method of ventilation. We therefore compared the effects of Pao and Ptr regulated VAV on breathing pattern and inspiratory effort.
  
  
  METHODS
  In seven intubated patients, flow, volume, Pao, Ptr, esophageal and transdiaphragmatic pressure were measured during VAV (0-80% respiratory system elastance) using Pao vs Ptr to regulate ventilator applied pressure. Breathing pattern and the pressure-time integral of the inspiratory muscles (integralP(mus) . dt) and diaphragm (integralP(di) . dt) were determined.
  
  
  RESULTS
  Compared to spontaneous breathing, the respiratory rate to tidal volume ratio, or rapid shallow breathing index (RSBI), improved progressively with increasing VAV (130 +/- 64 vs 70 +/- 35, VAV 0 vs 80%; P < 0.05) while inspiratory effort fell (integralP(mus) . dt = 39.6 +/- 7.5 vs 28.5 +/- 7.2 cm H(2)O.sec.L(-1), integralP(di) . dt, = 35.4 +/- 7.8 vs 24.2 +/- 5.9 cm H(2)O.sec.L(-1), VAV 0 vs 80%; P < 0.05) due to a decrease in elastic related effort. At any given level of support, there was further reduction in RSBI, integralP(mus) . dt, and integralP(di) . dt (which averaged 23.6 +/- 2.7, 33.7 +/- 4.4, and 38.5 +/- 5.1%, respectively; P < 0.05) for Ptr compared to Pao regulated VAV due to a decrease in resistive effort.
  
  
  CONCLUSIONS
  Tracheal pressure regulated VAV can be a simple and effective method of partial ventilatory support in acute respiratory failure. Further work will be needed to determine its efficacy and potential benefit relative to PAV and other modes of ventilation in routine clinical practice.
authors.affiliation: McGill University Health Centre, Royal Victoria Hospital, 687 Pine Avenue West, Room M4.10, Montreal, Quebec H3A 1A1, Canada. stewart.gottfried@muhc.mcgill.ca.
authors.forename: Tomislav
authors.initials: T
authors.lastname: Mirkovic
authors.forename: Vesna
authors.initials: V
authors.lastname: Paver-Erzen
authors.forename: Tomislav
authors.initials: T
authors.lastname: Klokocovnik
authors.forename: Ashvini
authors.initials: A
authors.lastname: Gursahaney
authors.forename: Paul
authors.initials: P
authors.lastname: Hernandez
authors.forename: Stewart B
authors.initials: SB
authors.lastname: Gottfried
mesh_terms: D000208:Acute Disease; D000368:Aged; D003627:Data Interpretation, Statistical; D003964:Diaphragm / Q000503:physiopathology; D005260:Female; D006801:Humans; D007442:Intubation, Intratracheal; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D011175:Positive-Pressure Respiration; D011312:Pressure; D012121:Respiration, Artificial; D012131:Respiratory Insufficiency / Q000503:physiopathology / Q000628:therapy*; D015656:Respiratory Mechanics / Q000502:physiology; D012132:Respiratory Muscles / Q000503:physiopathology; D013990:Tidal Volume / Q000502:physiology; D014132:Trachea / Q000502:physiology* / Q000503:physiopathology; D014159:Transducers
chemical_list: D010100:Oxygen