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      Physiologic effects of alveolar recruitment and inspiratory pauses during moderately-high-frequency ventilation delivered by a conventional ventilator in a severe lung injury model

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          Abstract

          Background and aims

          To investigate whether performing alveolar recruitment or adding inspiratory pauses could promote physiologic benefits (VT) during moderately-high-frequency positive pressure ventilation (MHFPPV) delivered by a conventional ventilator in a porcine model of severe acute respiratory distress syndrome (ARDS).

          Methods

          Prospective experimental laboratory study with eight pigs. Induction of acute lung injury with sequential pulmonary lavages and injurious ventilation was initially performed. Then, animals were ventilated on a conventional mechanical ventilator with a respiratory rate (RR) = 60 breaths/minute and PEEP titrated according to ARDS Network table. The first two steps consisted of a randomized order of inspiratory pauses of 10 and 30% of inspiratory time. In final step, we removed the inspiratory pause and titrated PEEP, after lung recruitment, with the aid of electrical impedance tomography. At each step, PaCO 2 was allowed to stabilize between 57–63 mmHg for 30 minutes.

          Results

          The step with RR of 60 after lung recruitment had the highest PEEP when compared with all other steps (17 [16,19] vs 14 [10, 17]cmH 2O), but had lower driving pressures (13 [13,11] vs 16 [14, 17]cmH 2O), higher P/F ratios (212 [191,243] vs 141 [105, 184] mmHg), lower shunt (23 [20, 23] vs 32 [27, 49]%), lower dead space ventilation (10 [0, 15] vs 30 [20, 37]%), and a more homogeneous alveolar ventilation distribution. There were no detrimental effects in terms of lung mechanics, hemodynamics, or gas exchange. Neither the addition of inspiratory pauses or the alveolar recruitment maneuver followed by decremental PEEP titration resulted in further reductions in VT.

          Conclusions

          During MHFPPV set with RR of 60 bpm delivered by a conventional ventilator in severe ARDS swine model, neither the inspiratory pauses or PEEP titration after recruitment maneuver allowed reduction of VT significantly, however the last strategy decreased driving pressures and improved both shunt and dead space.

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          Most cited references21

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          Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome.

          In patients with the acute respiratory distress syndrome, massive alveolar collapse and cyclic lung reopening and overdistention during mechanical ventilation may perpetuate alveolar injury. We determined whether a ventilatory strategy designed to minimize such lung injuries could reduce not only pulmonary complications but also mortality at 28 days in patients with the acute respiratory distress syndrome. We randomly assigned 53 patients with early acute respiratory distress syndrome (including 28 described previously), all of whom were receiving identical hemodynamic and general support, to conventional or protective mechanical ventilation. Conventional ventilation was based on the strategy of maintaining the lowest positive end-expiratory pressure (PEEP) for acceptable oxygenation, with a tidal volume of 12 ml per kilogram of body weight and normal arterial carbon dioxide levels (35 to 38 mm Hg). Protective ventilation involved end-expiratory pressures above the lower inflection point on the static pressure-volume curve, a tidal volume of less than 6 ml per kilogram, driving pressures of less than 20 cm of water above the PEEP value, permissive hypercapnia, and preferential use of pressure-limited ventilatory modes. After 28 days, 11 of 29 patients (38 percent) in the protective-ventilation group had died, as compared with 17 of 24 (71 percent) in the conventional-ventilation group (P<0.001). The rates of weaning from mechanical ventilation were 66 percent in the protective-ventilation group and 29 percent in the conventional-ventilation group (P=0.005): the rates of clinical barotrauma were 7 percent and 42 percent, respectively (P=0.02), despite the use of higher PEEP and mean airway pressures in the protective-ventilation group. The difference in survival to hospital discharge was not significant; 13 of 29 patients (45 percent) in the protective-ventilation group died in the hospital, as compared with 17 of 24 in the conventional-ventilation group (71 percent, P=0.37). As compared with conventional ventilation, the protective strategy was associated with improved survival at 28 days, a higher rate of weaning from mechanical ventilation, and a lower rate of barotrauma in patients with the acute respiratory distress syndrome. Protective ventilation was not associated with a higher rate of survival to hospital discharge.
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            Experimental pulmonary edema due to intermittent positive pressure ventilation with high inflation pressures. Protection by positive end-expiratory pressure.

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              Epidemiology and outcomes of acute lung injury.

              Acute lung injury (ALI) and its presentation with more severe hypoxemia, the ARDS, is a challenging entity for clinical investigation because, like many critical illness syndromes, it lacks an accepted diagnostic test and relies on a constellation of clinical findings for diagnosis. Despite these barriers, there have been important advances in the clinical and population epidemiology of ALI. This article will review recent studies of the incidence, diagnosis, etiologic and prognostic factors, relevant disease subsets, mortality, and long-term outcomes of ALI. A detailed understanding of the epidemiology and outcomes of ALI is essential for future research on mechanisms of both the acute presentation and long-term sequelae, for designing studies to identify genetic risk factors for developing ALI, and to develop strategies to treat or prevent the morbidity encountered by survivors.
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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Writing – original draft
                Role: ConceptualizationRole: InvestigationRole: MethodologyRole: Project administrationRole: ResourcesRole: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Project administration
                Role: ConceptualizationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Project administrationRole: ResourcesRole: SupervisionRole: Writing – original draft
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Project administrationRole: SupervisionRole: ValidationRole: Writing – original draftRole: Writing – review & editing
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                29 September 2017
                2017
                : 12
                : 9
                : e0185769
                Affiliations
                [1 ] Research and Education Institute, Hospital Sírio-Libanês, São Paulo, Brazil
                [2 ] Cardio-Pulmonary Department, Pulmonary Division, Heart Institute (Incor), University of São Paulo, São Paulo, Brazil
                [3 ] Intensive Care Unit, Hospital Israelita Albert Einstein, São Paulo, Brazil
                [4 ] Intensive Care Unit, Hospital Alemão Oswaldo Cruz, São Paulo, Brazil
                [5 ] Emergency Medicine Discipline, Universidade de São Paulo, São Paulo, Brazil
                University of Bari, ITALY
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Author information
                http://orcid.org/0000-0001-7521-399X
                Article
                PONE-D-17-13204
                10.1371/journal.pone.0185769
                5621701
                28961282
                2f638cc6-d642-4df9-839c-7343f533e298
                © 2017 Cordioli et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 5 April 2017
                : 19 September 2017
                Page count
                Figures: 3, Tables: 2, Pages: 12
                Funding
                The authors are grateful to the Research and Education Institute, Hospital Sírio - Libanês, São Paulo Brazil and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), São Paulo, Brazil for the Grant offered to the study development. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Medicine and Health Sciences
                Pulmonology
                Pulmonary Function
                Tidal Volume
                Medicine and Health Sciences
                Vascular Medicine
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                Biology and Life Sciences
                Physiology
                Respiratory Physiology
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                Physiology
                Respiratory Physiology
                Engineering and Technology
                Equipment
                Laboratory Equipment
                Ventilators
                Research and Analysis Methods
                Experimental Organism Systems
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                Pig Models
                Medicine and Health Sciences
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                Acute Respiratory Distress Syndrome
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                Critical Care and Emergency Medicine
                Respiratory Failure
                Acute Respiratory Distress Syndrome
                Medicine and Health Sciences
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                Respiratory Failure
                Acute Respiratory Distress Syndrome
                Biology and Life Sciences
                Anatomy
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                Blood Vessels
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                Biology and Life Sciences
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