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Zero expiratory pressure and low oxygen concentration promote heterogeneity of regional ventilation and lung densities
Author(s) -
Borges J. B.,
Porra L.,
Pellegrini M.,
Tannoia A.,
Derosa S.,
Larsson A.,
Bayat S.,
Perchiazzi G.,
Hedenstierna G.
Publication year - 2016
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/aas.12719
Subject(s) - medicine , ventilation (architecture) , mechanical ventilation , lung , positive end expiratory pressure , respiratory system , coefficient of variation , respiratory physiology , cardiology , mathematics , statistics , mechanical engineering , engineering
Background It is not well known what is the main mechanism causing lung heterogeneity in healthy lungs under mechanical ventilation. We aimed to investigate the mechanisms causing heterogeneity of regional ventilation and parenchymal densities in healthy lungs under anesthesia and mechanical ventilation. Methods In a small animal model, synchrotron imaging was used to measure lung aeration and regional‐specific ventilation ( sV̇ ). Heterogeneity of ventilation was calculated as the coefficient of variation in sV̇ ( CV sV̇ ). The coefficient of variation in lung densities ( CV D ) was calculated for all lung tissue, and within hyperinflated, normally and poorly aerated areas. Three conditions were studied: zero end‐expiratory pressure ( ZEEP ) and F I O 2 0.21; ZEEP and F I O 2 1.0; PEEP 12 cmH 2 O and F I O 2 1.0 (Open Lung‐ PEEP = OLP ). Results The mean tissue density at OLP was lower than ZEEP ‐1.0 and ZEEP ‐0.21. There were larger subregions with low sV̇ and poor aeration at ZEEP ‐0.21 than at OLP : 12.9 ± 9.0 vs. 0.6 ± 0.4% in the non‐dependent level, and 17.5 ± 8.2 vs. 0.4 ± 0.1% in the dependent one ( P = 0.041). The CV sV̇ of the total imaged lung at PEEP 12 cmH 2 O was significantly lower than on ZEEP , regardless of F I O 2 , indicating more heterogeneity of ventilation during ZEEP (0.23 ± 0.03 vs. 0.54 ± 0.37, P = 0.049). CV D changed over the different mechanical ventilation settings ( P = 0.011); predominantly, CV D increased during ZEEP . The spatial distribution of the CV D calculated for the poorly aerated density category changed with the mechanical ventilation settings, increasing in the dependent level during ZEEP . Conclusion ZEEP together with low F I O 2 promoted heterogeneity of ventilation and lung tissue densities, fostering a greater amount of airway closure and ventilation inhomogeneities in poorly aerated regions.