A lung computed tomography assessment of positive end-expiratory pressureinduced lung overdistention
DOI:
https://doi.org/10.22491/2357-9730.125244Keywords:
Acute lung injury, acute respiratory distress syndrome, computerized tomography, alveolar recruitment, hyperdistension, positive end-expiratory pressureAbstract
OBJECTIVE: The aim of the present study was to establish the tomographic limit of lung overdistention in normal individuals as well as to assess positive end-expiratory
pressure-induced overdistention and alveolar recruitment in patients with acute lung injury.
MATERIALS AND METHODS: Lung distention was first determined in six healthy volunteers in whom computed tomographic sections were obtained at functional
residual capacity and total lung capacity with a positive airway pressure of 30 cmH2O. Tomographic scans at zero end-expiratory pressure and positive end-expiratory
pressure were performed in six patients with acute lung injury. Computed tomographies were performed from the apex to the diaphragm and lung volumes were quantified by the analysis of the density histograms.
RESULTS: Analysis of the density histograms in healthy volunteers was monophasic with a peak at -791 ± 12 Housenfield units. In total lung capacity, lung volume
increased by 79 ± 35% and the peak of lung density decreased to -886 ±26 Housenfield units. More than 70% of the increase in lung volume was located below
-900 Housenfield units, suggesting that this value can be considered as the threshold separating normal aeration from overdistention. In patients with acute lung injury, at
zero end-expiratory pressure the distribution of density histograms was either monophasic (n=3) or biphasic (n=3), with mean density of -319 ± 34 Housenfield
units. With positive end-expiratory pressure application, lung volume increased by 47 ± 19%, while lung density decreased to -538 ± Housenfield units. Positive endexpiratory pressure induced a mean alveolar recruitment of 238 ±320 ml.
CONCLUSIONS: The limit of overdistention in healthy individuals was -900 Housenfield units. This threshold can be used in patients with acute lung injury for
differentiating alveolar recruitment from lung overdistention.
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