title: Bedside assessment of the effects of positive end-expiratory pressure on lung inflation and recruitment by the helium dilution technique and electrical impedance tomography.
abstract: OBJECTIVE
  Higher positive end-expiratory pressure might induce lung inflation and recruitment, yielding enhanced regional lung protection. We measured positive end-expiratory pressure-related lung volume changes by electrical impedance tomography and by the helium dilution technique. We also used electrical impedance tomography to assess the effects of positive end-expiratory pressure on regional determinants of ventilator-induced lung injury.
  
  
  METHODS
  A prospective randomized crossover study was performed on 20 intubated adult patients: 12 with acute hypoxemic respiratory failure and 8 with acute respiratory distress syndrome. Each patient underwent protective controlled ventilation at lower (7 [7, 8] cmH2O) and higher (12 [12, 13] cmH2O) positive end-expiratory pressures. At the end of each phase, we collected ventilation, helium dilution, and electrical impedance tomography data.
  
  
  RESULTS
  Positive end-expiratory pressure-induced changes in lung inflation and recruitment measured by electrical impedance tomography and helium dilution showed close correlations (R (2) = 0.78, p < 0.001 and R (2) = 0.68, p < 0.001, respectively) but with relatively variable limits of agreement. At higher positive end-expiratory pressure, recruitment was evident in all lung regions (p < 0.01) and heterogeneity of tidal ventilation distribution was reduced by increased tidal volume distending the dependent lung (p < 0.001); in the non-dependent lung, on the other hand, compliance decreased (p < 0.001) and tidal hyperinflation significantly increased (p < 0.001). In the subgroup of ARDS patients (but not in the whole study population) tidal hyperinflation in the dependent lung regions decreased at higher positive end-expiratory pressure (p = 0.05), probably indicating higher potential for recruitment.
  
  
  CONCLUSIONS
  Close correlations exist between bedside assessment of positive end-expiratory pressure-induced changes in lung inflation and recruitment by the helium dilution and electrical impedance tomography techniques. Higher positive end-expiratory pressure exerts mixed effects on the regional determinants of ventilator-induced lung injury; these merit close monitoring.
authors: Department of Anesthesia, Critical Care and Emergency, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via F. Sforza 35, 20122, Milan, Italy.
authors: Tommaso
authors: T
authors: Mauri
authors: Department of Emergency, San Gerardo Hospital, Monza, Italy.
authors: Nilde
authors: N
authors: Eronia
authors: Department of Anesthesia, Critical Care and Emergency, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via F. Sforza 35, 20122, Milan, Italy.
authors: Cecilia
authors: C
authors: Turrini
authors: Department of Anesthesia, Critical Care and Emergency, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via F. Sforza 35, 20122, Milan, Italy.
authors: Marta
authors: M
authors: Battistini
authors: Department of Anesthesia, Critical Care and Emergency, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via F. Sforza 35, 20122, Milan, Italy.
authors: Giacomo
authors: G
authors: Grasselli
authors: Department of Emergency, San Gerardo Hospital, Monza, Italy.
authors: Roberto
authors: R
authors: Rona
authors: Department of Morphology, Surgery and Experimental Medicine, Section of Anesthesia and Intensive Care, University of Ferrara, Ferrara, Italy.
authors: Carlo Alberto
authors: CA
authors: Volta
authors: Department of Emergency, San Gerardo Hospital, Monza, Italy.|Department of Medicine and Surgery, University of Milan-Bicocca, Monza, Italy.
authors: Giacomo
authors: G
authors: Bellani
authors: Department of Anesthesia, Critical Care and Emergency, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Via F. Sforza 35, 20122, Milan, Italy. antonio.pesenti@unimi.it.|Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy. antonio.pesenti@unimi.it.
authors: Antonio
authors: http://orcid.org/0000-0003-2593-729X
authors: A
authors: Pesenti
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018592:Cross-Over Studies; D017097:Electric Impedance / Q000627:therapeutic use*; D005260:Female; D006371:Helium / Q000627:therapeutic use*; D006801:Humans; D008176:Lung Volume Measurements / Q000379:methods; D008297:Male; D008875:Middle Aged; D000067716:Point-of-Care Testing; D011175:Positive-Pressure Respiration / Q000379:methods*; D011446:Prospective Studies; D012128:Respiratory Distress Syndrome / Q000628:therapy; D012131:Respiratory Insufficiency / Q000628:therapy; D013990:Tidal Volume; D014054:Tomography / Q000379:methods*; D055397:Ventilator-Induced Lung Injury / Q000209:etiology
chemical_list: D006371:Helium
keywords: Acute respiratory distress syndrome; Electrical impedance; Lung volume measurements; Mechanical ventilation; Positive end-expiratory pressure; Ventilator-induced lung injury