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The Open Lung Approach Improves Pulmonary Vascular Mechanics in an Experimental Model of Acute Respiratory Distress Syndrome
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory.
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2017 (English)In: Critical Care Medicine, ISSN 0090-3493, E-ISSN 1530-0293, Vol. 45, no 3, p. e298-e305Article in journal (Refereed) Published
Abstract [en]

OBJECTIVE: To test whether positive end-expiratory pressure consistent with an open lung approach improves pulmonary vascular mechanics compared with higher or lower positive end-expiratory pressures in experimental acute respiratory distress syndrome.

DESIGN: Experimental study.

SETTING: Animal research laboratory.

SUBJECTS: Ten pigs, 35 ± 5.2 kg.

INTERVENTIONS: Acute respiratory distress syndrome was induced combining saline lung lavages with injurious mechanical ventilation. The positive end-expiratory pressure level resulting in highest compliance during a decremental positive end-expiratory pressure trial after lung recruitment was determined. Thereafter, three positive end-expiratory pressure levels were applied in a random order: hyperinflation, 6 cm H2O above; open lung approach, 2 cm H2O above; and collapse, 6 cm H2O below the highest compliance level. High fidelity pressure and flow sensors were placed at the main pulmonary artery for measuring pulmonary artery resistance (Z0), effective arterial elastance, compliance, and reflected pressure waves.

MEASUREMENTS AND MAIN RESULTS: After inducing acute respiratory distress syndrome, Z0 and effective arterial elastance increased (from 218 ± 94 to 444 ± 115 dyn.s.cm and from 0.27 ± 0.14 to 0.62 ± 0.22 mm Hg/mL, respectively; p < 0.001), vascular compliance decreased (from 2.76 ± 0.86 to 1.48 ± 0.32 mL/mm Hg; p = 0.003), and reflected waves arrived earlier (0.23 ± 0.07 vs 0.14 ± 0.05, arbitrary unit; p = 0.002) compared with baseline. Comparing the three positive end-expiratory pressure levels, open lung approach resulted in the lowest: 1) Z0 (297 ± 83 vs 378 ± 79 dyn.s.cm, p = 0.033, and vs 450 ± 119 dyn.s.cm, p = 0.002); 2) effective arterial elastance (0.37 ± 0.08 vs 0.50 ± 0.15 mm Hg/mL, p = 0.04, and vs 0.61 ± 0.12 mm Hg/mL, p < 0.001), and 3) reflection coefficient (0.35 ± 0.17 vs 0.48 ± 0.10, p = 0.024, and vs 0.53 ± 0.19, p = 0.005), comparisons with hyperinflation and collapse, respectively.

CONCLUSIONS: In this experimental setting, positive end-expiratory pressure consistent with the open lung approach resulted in the best pulmonary vascular mechanics compared with higher or lower positive end-expiratory pressure settings.

Place, publisher, year, edition, pages
2017. Vol. 45, no 3, p. e298-e305
Keywords [en]
Fluid responsiveness, Spontaneous breathing, Head-up tilt, Pulse pressure variation, Stroke volume variation, Systolic pressure variation
National Category
Anesthesiology and Intensive Care
Identifiers
URN: urn:nbn:se:uu:diva-307915DOI: 10.1097/CCM.0000000000002082PubMedID: 27763913OAI: oai:DiVA.org:uu-307915DiVA, id: diva2:1048834
Available from: 2016-11-22 Created: 2016-11-22 Last updated: 2018-01-12Bibliographically approved
In thesis
1. Hemodynamic Effects of Lung Function Optimization in Experimental Acute Respiratory Distress Syndrome
Open this publication in new window or tab >>Hemodynamic Effects of Lung Function Optimization in Experimental Acute Respiratory Distress Syndrome
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Acute Respiratory Distress Syndrome (ARDS) is a severe pulmonary inflammation affecting thousands of patients every year in Sweden and has a mortality of 30-50%. Mechanical ventilation (MV) is usually necessary, but could per se augment the inflammation and contribute to mortality. MV strategies protective for the lung parenchyma have been developed but without considering the pulmonary circulation or the right heart ventricle (RV) that also are affected in ARDS. MV should ideally be optimized to protect both the lung parenchyma and the RV/pulmonary vasculature. My hypothesis was that MV that prevents alveolar collapse and overdistension, i.e., the “open lung approach (OLA)” would be optimal. The aims of this project were 1) to carefully describe the pulmonary vascular mechanics (PVM) in ARDS compared with healthy lungs, 2) to assess how different ventilatory methods influence PVM, and 3) to propose a ventilatory method that protects both lung parenchyma and circulation.

In a porcine model, high fidelity pressure and flow sensors were applied directly on the main pulmonary artery to evaluate steady and oscillatory components of PVM.  In this way a complete PVM description was obtained for normal and injured lungs at different MV. In particular, the effects of OLA were compared with standard MV and, in addition, with MV methods where overdistension or collapse were present.

Results: 1) Compared with collapse or overdistension, OLA provided better PVM. 2) The effects on PVM of OLA and the standard protective MV were similar. 3) Early ARDS augmented the effects of pulse wave reflection on PVM leading to a situation in which the RV had to increase its work to maintain adequate blood flow. Thus, a part of this work was wasted by the effect of wave reflections, making the RV/pulmonary vasculature inefficient. 4) Tidal breathing affected PVM cyclically and this effect was enhanced in ARDS compared with healthy lungs.

In conclusion, ARDS and different ventilatory methods, as well as tidal ventilation per se, affected PVM. OLA improved PVM compared with other MV settings where significant collapse and overdistension were allowed. However, OLA was not superior to standard protective MV.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 60
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1419
Keywords
Acute respiratory distress syndrome, Lung protective ventilation, Mechanical ventilation, Open lung approach, Pulmonary heart disease, Pulmonary vascular mechanics, Pulmonary vascular dysfunction, Pulse wave analysis, Right ventricular dysfunction
National Category
Physiology Anesthesiology and Intensive Care
Research subject
Anaesthesiology and Intensive Care; Physiology
Identifiers
urn:nbn:se:uu:diva-338688 (URN)978-91-513-0210-2 (ISBN)
Public defence
2018-03-08, Rosen, Akademiska sjukhuset 75185 Uppsala, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2018-02-13 Created: 2018-01-12 Last updated: 2018-03-07

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Santos, ArnoldoBatista Borges, JoãoHedenstierna, GöranLarsson, AndersSuarez-Sipmann, Fernando

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