title: Assessment of Factors Related to Auto-PEEP.
abstract: BACKGROUND
  Previous physiological studies have identified factors that are involved in auto-PEEP generation. In our study, we examined how much auto-PEEP is generated from factors that are involved in its development.
  
  
  METHODS
  One hundred eighty-six subjects undergoing controlled mechanical ventilation with persistent expiratory flow at the beginning of each inspiration were enrolled in the study. Volume-controlled continuous mandatory ventilation with PEEP of 0 cm H2O was applied while maintaining the ventilator setting as chosen by the attending physician. End-expiratory and end-inspiratory airway occlusion maneuvers were performed to calculate respiratory mechanics, and tidal flow limitation was assessed by a maneuver of manual compression of the abdomen.
  
  
  RESULTS
  The variable with the strongest effect on auto-PEEP was flow limitation, which was associated with an increase of 2.4 cm H2O in auto-PEEP values. Moreover, auto-PEEP values were directly related to resistance of the respiratory system and body mass index and inversely related to expiratory time/time constant. Variables that were associated with the breathing pattern (tidal volume, frequency minute ventilation, and expiratory time) did not show any relationship with auto-PEEP values. The risk of auto-PEEP ≥5 cm H2O was increased by flow limitation (adjusted odds ratio 17; 95% CI: 6-56.2), expiratory time/time constant ratio <1.85 (12.6; 4.7-39.6), respiratory system resistance >15 cm H2O/L s (3; 1.3-6.9), age >65 y (2.8; 1.2-6.5), and body mass index >26 kg/m(2) (2.6; 1.1-6.1).
  
  
  CONCLUSIONS
  Flow limitation, expiratory time/time constant, resistance of the respiratory system, and obesity are the most important variables that affect auto-PEEP values. Frequency expiratory time, tidal volume, and minute ventilation were not independently associated with auto-PEEP. Therapeutic strategies aimed at reducing auto-PEEP and its adverse effects should be primarily oriented to the variables that mainly affect auto-PEEP values.
authors.affiliation: Department of Anesthesia and Intensive Care, Fondazione Poliambulanza Hospital, Brescia, Italy. giuseppe.natalini@gmail.com.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Natalini
authors.affiliation: Department of Anesthesia and Intensive Care, Spedali Civili Hospital, Brescia, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Tuzzo
authors.affiliation: Department of Anesthesia and Intensive Care, Fondazione Poliambulanza Hospital, Brescia, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Rosano
authors.affiliation: Department of Anesthesia and Intensive Care, SS Annunziata Hospital, Savigliano, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Testa
authors.affiliation: Department of Anesthesia and Intensive Care, Fondazione Poliambulanza Hospital, Brescia, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Grazioli
authors.affiliation: Department of Anesthesia and Intensive Care, Misericordia Hospital, Grosseto, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Pennestrì
authors.affiliation: Department of Anesthesia and Intensive Care, San Giovanni Bosco Hospital, Napoli, Italy.
authors.forename: Guido
authors.initials: G
authors.lastname: Amodeo
authors.affiliation: Department of Anesthesia and Intensive Care, Cardarelli Hospital, Napoli, Italy.
authors.forename: Paolo F
authors.initials: PF
authors.lastname: Marsilia
authors.affiliation: Department of Anesthesia and Intensive Care, Mellino Mellini Hospital, Chiari, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Tinnirello
authors.affiliation: Department of Anesthesia and Intensive Care, Agnelli Hospital, Pinerolo, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Berruto
authors.affiliation: Department of Anesthesia and Intensive Care, Santa Maria degli Angeli Hospital, Pordenone, Italy.
authors.forename: Marialinda
authors.initials: M
authors.lastname: Fiorillo
authors.affiliation: Department of Anesthesia, Critical Care Medicine, and Emergency, University of Brescia at Spedali Civili, Brescia, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Filippini
authors.affiliation: Department of Anesthesia and Intensive Care, Cattinara Hospital, Trieste, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Peratoner
authors.affiliation: Respiratory Epidemiology, Occupational Medicine & Public Health, Imperial College, London, United Kingdom.
authors.forename: Cosetta
authors.initials: C
authors.lastname: Minelli
authors.affiliation: Department of Anesthesia and Intensive Care, Fondazione Poliambulanza Hospital, Brescia, Italy.
authors.forename: Achille
authors.initials: A
authors.lastname: Bernardini
mesh_terms: D000367:Age Factors; D000368:Aged; D000402:Airway Obstruction / Q000150:complications* / Q000503:physiopathology; D000403:Airway Resistance / Q000502:physiology; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D005540:Forced Expiratory Flow Rates / Q000502:physiology; D006801:Humans; D007320:Inspiratory Capacity / Q000502:physiology; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D018467:Positive-Pressure Respiration, Intrinsic / Q000209:etiology* / Q000503:physiopathology; D011312:Pressure; D012121:Respiration, Artificial / Q000379:methods; D015656:Respiratory Mechanics / Q000502:physiology*; D013990:Tidal Volume
keywords: artificial; intrinsic; positive-pressure respiration; respiration; respiratory function tests; respiratory insufficiency; respiratory mechanics; respiratory physiological phenomena