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      Continuous external negative pressure improves oxygenation and respiratory mechanics in Experimental Lung Injury in Pigs – A pilot proof-of-concept trial

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          Abstract

          Background

          Continuous external negative pressure (CENP) during positive pressure ventilation can recruit dependent lung regions. We hypothesised that CENP applied regionally to the thorax or the abdomen only, increases the caudal end-expiratory transpulmonary pressure depending on positive end-expiratory pressure (PEEP) in lung-injured pigs. Eight pigs were anesthetised and mechanically ventilated in the supine position. Pressure sensors were placed in the left pleural space, and a lung injury was induced by saline lung lavages. A CENP shell was placed at the abdomen and thorax (randomised order), and animals were ventilated with PEEP 15, 7 and zero cmH 2O (15 min each). On each PEEP level, CENP of − 40, − 30, − 20, − 10 and 0 cmH 2O was applied (3 min each). Respiratory and haemodynamic variables were recorded. Electrical impedance tomography allowed assessment of centre of ventilation.

          Results

          Compared to positive pressure ventilation alone, the caudal transpulmonary pressure was significantly increased by CENP of ≤ 20 cmH 2O at all PEEP levels. CENP of – 20 cmH 2O reduced the mean airway pressure at zero PEEP ( P = 0.025). The driving pressure decreased at CENP of ≤ 10 at PEEP of 0 and 7 cmH 2O ( P < 0.001 each) but increased at CENP of – 30 cmH 2O during the highest PEEP ( P = 0.001). CENP of – 30 cmH 2O reduced the mechanical power during zero PEEP ( P < 0.001). Both elastance ( P < 0.001) and resistance ( P < 0.001) were decreased at CENP ≤ 30 at PEEP of 0 and 7 cmH 2O. Oxygenation increased at CENP of ≤ 20 at PEEP of 0 and 7 cmH 2O ( P < 0.001 each). Applying external negative pressure significantly shifted the centre of aeration towards dorsal lung regions irrespectively of the PEEP level. Cardiac output decreased significantly at CENP -20 cmH 2O at all PEEP levels ( P < 0.001). Effects on caudal transpulmonary pressure, elastance and cardiac output were more pronounced when CENP was applied to the abdomen compared with the thorax.

          Conclusions

          In this lung injury model in pigs, CENP increased the end-expiratory caudal transpulmonary pressure. This lead to a shift of lung aeration towards dependent zones as well as improved respiratory mechanics and oxygenation, especially when CENP was applied to the abdomen as compared to the thorax. CENP values ≤ 20 cmH 2O impaired the haemodynamics.

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          Is mechanical power the final word on ventilator-induced lung injury?—no

          Despite being a promising idea that combines several variables related to ventilator-induced lung injury (VILI), the concept of mechanical power (MP) carries a number of limitations, leaves several open questions, lacks proper modelling of positive end-expiratory pressure (PEEP) effects and, more importantly, does not respect the amount of lung tissue subjected to MP. First, the assessment of MP as a measure for development of VILI would have the highest relevance when volume displacement and related pressure changes are measured directly within the lung. Thus, ideally the relationship between MP delivered to the total respiratory system, and that delivered to lung tissue is discerned. Second, MP as defined today relates to the inspiratory phase only, and it is very possible that the expiratory phase will also play a role. Third, the calculation of MP during spontaneous breathing is challenging as airway pressure, flow and esophageal pressure are affected counter-directionally and simultaneously overlapping by the action of the ventilator and the respiratory muscles. Fourth, in its current form, MP is modelled with a positive linear relationship with PEEP, which is based on incorrect mathematical modelling to integrate the role of PEEP into MP. Fifth, the present equation used to calculate MP is qualitatively in disagreement with clinical data on VILI. The reduction of MP to its elastic part, might not only result in a higher association with VILI, but also amplifies an indirect U-shaped relationship with PEEP.
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            Cardiovascular effects of mechanical ventilation.

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              Validation of esophageal pressure occlusion test after paralysis.

              Measurements of respiratory mechanics are frequently made in ventilated infants and children. Esophageal pressure measurements (Pes) using a balloon on a catheter have been used to partition the respiratory mechanics into lung and chest wall components. Appropriate positioning of this balloon is crucial to obtain accurate estimates of pleural pressure. Traditionally, in spontaneously breathing subjects the balloon position is assessed with an occlusion test. In ventilated subjects, it is not always possible to perform an occlusion test prior to paralysis, and even if such a test is performed it may be relevant under conditions of positive pressure ventilation. By occluding the airway opening and applying gentle pressure to the abdomen or rib cage, positive swings in pressure can be measured by both Pes and airway opening pressure (Pao). We compared traditional occlusion tests measured in 16 spontaneously breathing puppies to the positive pressure occlusion test performed after paralysis. In 2 pups we were unable to obtain a reasonable traditional occlusion test (> 15% difference between Pes and Pao) but we obtained 10 traditional occlusion tests in each of the remaining 14 pups (2.1-14 kg). In 11 of these animals delta Pes was within 10% of delta Pao. This compared well to positive pressure occlusion test using abdominal pressure performed after analysis, where delta Pes was within 10% of delta Pao in 10 animals. In 9 of these pups occlusion tests were also performed by applying pressure on the rib cage, where delta Pes was within 10% of delta Pao in 6 animals.(ABSTRACT TRUNCATED AT 250 WORDS)
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                Author and article information

                Contributors
                robert.huhle@tu-dresden.de
                Conference
                Intensive Care Med Exp
                Intensive Care Med Exp
                Intensive Care Medicine Experimental
                Springer International Publishing (Cham )
                2197-425X
                18 December 2020
                18 December 2020
                December 2020
                : 8
                : Suppl 1
                : 49
                Affiliations
                [1 ]GRID grid.412282.f, ISNI 0000 0001 1091 2917, Pulmonary Engineering Group, Dept. of Anaesthesiology and Intensive Care Medicine, , University Hospital Carl Gustav Carus at Technische Universität Dresden, ; Fetscherstrasse 74, 01307 Dresden, Germany
                [2 ]GRID grid.4708.b, ISNI 0000 0004 1757 2822, Department of Pathophysiology and Transplantation, , University of Milan, ; Via Francesco Sforza 35, 20122 Milano, Italia
                [3 ]GRID grid.416052.4, ISNI 0000 0004 1755 4122, Devision of Respiratory Physiopathology, , Monaldi Hospital, ; Naples, Italy
                Author information
                http://orcid.org/0000-0003-2185-1819
                Article
                315
                10.1186/s40635-020-00315-1
                7746426
                3a101fc8-5bed-47b2-a6f8-36186a9fd120
                © The Author(s) 2020

                Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

                4th International Symposium on Acute Pulmonary Injury and Translational Research - INSPIRES 2019
                INSPIRES IV
                Dresden, Germany
                25-26 November 2019
                History
                : 9 June 2020
                : 11 June 2020
                Categories
                Research
                Custom metadata
                © The Author(s) 2020

                continuous external negative pressure,cenp,negative pressure ventilation,mechanical ventilation,acute respiratory distress syndrome,ards,lung mechanics,pleural pressure,transpulmonary pressure,electrical impedance tomography

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