title: Patient-ventilator interaction during pressure support ventilation and neurally adjusted ventilatory assist.
abstract: OBJECTIVE
  To compare the effect of pressure support ventilation and neurally adjusted ventilatory assist on breathing pattern, patient-ventilator synchrony, diaphragm unloading, and gas exchange. Increasing the level of pressure support ventilation can increase tidal volume, reduce respiratory rate, and lead to delayed ventilator triggering and cycling. Neurally adjusted ventilatory assist uses diaphragm electrical activity to control the timing and pressure of assist delivery and is expected to enhance patient-ventilator synchrony.
  
  
  METHODS
  Prospective, comparative, crossover study.
  
  
  METHODS
  Adult critical care unit in a tertiary university hospital.
  
  
  METHODS
  Fourteen nonsedated mechanically ventilated patients (n = 12 with chronic obstructive pulmonary disease).
  
  
  METHODS
  Patients were ventilated for 10-min periods, using two pressure support ventilation levels (lowest tolerable and +7 cm H2O higher) and two neurally adjusted ventilatory assist levels (same peak pressures and external positive end-expiratory pressure as with pressure support ventilation), delivered in a randomized order.
  
  
  RESULTS
  Diaphragm electrical activity, respiratory pressures, air flow, volume, neural and ventilator respiratory rates, and arterial blood gases were measured. Peak pressures were 17 +/- 6 cm H2O and 24 +/- 6 cm H2O and 19 +/- 5 cm H2O and 24 +/- 6 cm H2O with high and low pressure support ventilation and neurally adjusted ventilatory assist, respectively. The breathing pattern was comparable with pressure support ventilation and neurally adjusted ventilatory assist during low assist; during higher assist, larger tidal volumes (p = .003) and lower breathing frequencies (p = .008) were observed with pressure support ventilation. Increasing the assist increased cycling delays only with pressure support ventilation (p = .003). Compared with pressure support ventilation, neurally adjusted ventilatory assist reduced delays of ventilator triggering (p < .001 for low and high assist) and cycling (high assist: p = .004; low assist: p = .04), and abolished wasted inspiratory efforts observed with pressure support ventilation in six subjects. The diaphragm electrical activity and pressure-time product for ventilator triggering were lower with neurally adjusted ventilatory assist (p = .005 and p = .02, respectively; analysis of variance). Arterial blood gases were similar with both modes.
  
  
  CONCLUSIONS
  Neurally adjusted ventilatory assist can improve patient-ventilator synchrony by reducing the triggering and cycling delays, especially at higher levels of assist, at the same time preserving breathing and maintaining blood gases.
authors.affiliation: Critical Care Unit, Sacré-Coeur Hospital, University of Montreal, Montreal, Quebec, Canada. jadranka.spahija@mcgill.ca
authors.forename: Jadranka
authors.initials: J
authors.lastname: Spahija
authors.forename: Michel
authors.initials: M
authors.lastname: de Marchie
authors.forename: Martin
authors.initials: M
authors.lastname: Albert
authors.forename: Patrick
authors.initials: P
authors.lastname: Bellemare
authors.forename: Stéphane
authors.initials: S
authors.lastname: Delisle
authors.forename: Jennifer
authors.initials: J
authors.lastname: Beck
authors.forename: Christer
authors.initials: C
authors.lastname: Sinderby
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D007385:Intermittent Positive-Pressure Ventilation / Q000379:methods; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial / Q000379:methods*; D056152:Respiratory Rate; D013990:Tidal Volume