title: Cycling-off modes during pressure support ventilation: effects on breathing pattern, patient effort, and comfort.
abstract: OBJECTIVE
  Expiratory asynchrony during pressure support ventilation (PSV) has been recognized as a cause of patient discomfort, increased workload, and impaired weaning process. We evaluated breathing pattern, patient comfort, and patient effort during PSV comparing 2 flow termination criteria: fixed at 5% of peak inspiratory flow vs automatic, real-time, breath-by-breath adjustment within the range of 5% to 55%.
  
  
  METHODS
  Randomized crossover clinical trial. Sixteen awake patients, in the process of weaning, under PSV for more than 24 hours were subjected to 3 phases of PSV, each lasting 1 hour and using 1 of the 2 aforementioned termination criteria.
  
  
  RESULTS
  Effective pressure support during automatic adjustment (AA) was 12.5±3.2 cm H2O vs 12.5±3.9 cm H2O (P=.9) with the fixed termination criterion, and external positive end-expiratory pressure was 6.2±1.8 vs 6.8±2 (P<.05). The effective termination criterion was higher during AA (31% [23-39] vs 12% [6-23]; P<.01), but without producing premature breath terminations. Pressure overshoots and alternative cycling-off were also decreased. Throughout the AA period, we observed a higher respiratory rate (24±8 breaths/min vs 19±6 breaths/min; P<.001), lower tidal volume (484 ± 88 mL vs 518±102 mL; P<.001), and shorter inspiratory times (1.0±0.3 seconds vs 1.3±0.3 seconds; P<.001). Automatic adjustment was associated with lower airway occlusion pressure after 0.1 second (P0.1) (1.8±0.9 cm H2O vs 2.4±1 cm H2O; P<.01), lower pressure-time product to trigger the ventilator, and lower subjective discomfort (visual analog scale, 3.7±1.3 vs 4.5±1.2; P<.001).
  
  
  CONCLUSIONS
  When compared with a fixed termination criterion, the use of a variable, real-time-adjusted termination criterion improved some indices of patient-ventilator synchrony, producing better breathing pattern, less discomfort, and slightly lower patient effort during PSV.
authors.affiliation: Intensive Care Unit, Hospital Mãe de Deus, Porto Alegre, Brazil; Graduate Program in Medical Sciences, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.
authors.forename: Fabrícia C
authors.initials: FC
authors.lastname: Hoff
authors.affiliation: Pulmonary Division, Heart Institute (INCOR), Hospital das Clinicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil.
authors.forename: Mauro R
authors.initials: MR
authors.lastname: Tucci
authors.affiliation: Pulmonary Division, Heart Institute (INCOR), Hospital das Clinicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil.
authors.forename: Marcelo B P
authors.initials: MB
authors.lastname: Amato
authors.affiliation: Graduate Program in Cardiology and Cardiovascular Sciences, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil; Physiotherapy Division, Universidade Luterana do Brasil, Torres, Brazil.
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Santos
authors.affiliation: Intensive Care Unit, Hospital Mãe de Deus, Porto Alegre, Brazil; Graduate Program in Medical Sciences, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil; Intensive Care Unit, Hospital de Clínicas de Porto Alegre, Porto Alegre, Brazil. Electronic address: josuev@terra.com.br.
authors.forename: Josué A
authors.initials: JA
authors.lastname: Victorino
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D018592:Cross-Over Studies; D045853:Exhalation / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D012119:Respiration; D056152:Respiratory Rate / Q000502:physiology*; D013312:Stress, Physiological; D013990:Tidal Volume; D013997:Time Factors; D015300:Ventilator Weaning / Q000379:methods*
keywords: Cycling-off criteria; Patient comfort; Patient ventilator interaction; Pressure support ventilation