title: Limited predictability of maximal muscular pressure using the difference between peak airway pressure and positive end-expiratory pressure during proportional assist ventilation (PAV).
abstract: BACKGROUND
  If the proportional assist ventilation (PAV) level is known, muscular effort can be estimated from the difference between peak airway pressure and positive end-expiratory pressure (PEEP) (ΔP) during PAV. We conjectured that deducing muscle pressure from ΔP may be an interesting method to set PAV, and tested this hypothesis using the oesophageal pressure time product calculation.
  
  
  METHODS
  Eleven mechanically ventilated patients with oesophageal pressure monitoring under PAV were enrolled. Patients were randomly assigned to seven assist levels (20-80%, PAV20 means 20% PAV gain) for 15 min. Maximal muscular pressure calculated from oesophageal pressure (Pmus, oes) and from ΔP (Pmus, aw) and inspiratory pressure time product derived from oesophageal pressure (PTPoes) and from ΔP (PTPaw) were determined from the last minute of each level. Pmus, oesand PTPoeswith consideration of PEEPi were expressed as Pmus, oes, PEEPiand PTPoes, PEEPi, respectively. Pressure time product was expressed as per minute (PTPoes, PTPoes, PEEPi, PTPaw) and per breath (PTPoes, br, PTPoes, PEEPi, br, PTPaw, br).
  
  
  RESULTS
  PAV significantly reduced the breathing effort of patients with increasing PAV gain (PTPoes214.3 ± 80.0 at PAV20 vs. 83.7 ± 49.3 cmH2O•s/min at PAV80, PTPoes, PEEPi277.3 ± 96.4 at PAV20 vs. 121.4 ± 71.6 cmH2O•s/min at PAV80, p < 0.0001). Pmus, awoverestimates Pmus, oesfor low-gain PAV and underestimates Pmus, oesfor moderate-gain to high-gain PAV. An optimal Pmus, awcould be achieved in 91% of cases with PAV60. When the PAV gain was adjusted to Pmus, awof 5-10 cmH2O, there was a 93% probability of PTPoes<224 cmH2O•s/min and 88% probability of PTPoes, PEEPi< 255 cmH2O•s/min.
  
  
  CONCLUSIONS
  Deducing maximal muscular pressure from ΔP during PAV has limited accuracy. The extrapolated pressure time product from ΔP is usually less than the pressure time product calculated from oesophageal pressure tracing. However, when the PAV gain was adjusted to Pmus, awof 5-10 cmH2O, there was a 90% probability of PTPoesand PTPoes, PEEPiwithin acceptable ranges. This information should be considered when applying ΔP to set PAV under various gains.
authors.affiliation: Section of Chest Medicine and Respiratory Care, Department of Internal Medicine, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Po-Lan
authors.initials: PL
authors.lastname: Su
authors.affiliation: Section of Chest Medicine and Respiratory Care, Department of Internal Medicine, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan.|Graduate Institute of Clinical Medical Sciences; Department of Respiratory Care, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Pei-Shan
authors.initials: PS
authors.lastname: Kao
authors.affiliation: Medical Intensive Care Unit, Department of Internal Medicine, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Wei-Chieh
authors.initials: WC
authors.lastname: Lin
authors.affiliation: Department of Statistics, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Pei-Fang
authors.initials: PF
authors.lastname: Su
authors.affiliation: Medical Intensive Care Unit, Department of Internal Medicine, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan. cwchen@mail.ncku.edu.tw.|Medical Device Innovation Center, National Cheng Kung University, Tainan, Taiwan. cwchen@mail.ncku.edu.tw.
authors.forename: Chang-Wen
authors.identifier: http://orcid.org/0000-0001-7954-4278
authors.initials: CW
authors.lastname: Chen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D004947:Esophagus / Q000502:physiology*; D005260:Female; D005544:Forecasting; D006801:Humans; D007362:Intensive Care Units / Q000592:standards*; D059725:Interactive Ventilatory Support / Q000379:methods / Q000592:standards*; D008297:Male; D008875:Middle Aged; D010366:Peak Expiratory Flow Rate / Q000502:physiology*; D011175:Positive-Pressure Respiration / Q000379:methods / Q000592:standards*; D011312:Pressure; D015656:Respiratory Mechanics / Q000502:physiology; D013990:Tidal Volume / Q000502:physiology
keywords: Airway pressure; Pressure time product; Proportional assist ventilation