Lung anatomy, energy load, and ventilator-induced lung injury.

Abstract

BACKGROUND:

High tidal volume can cause ventilator-induced lung injury (VILI), but positive end-expiratory pressure (PEEP) is thought to be protective. We aimed to find the volumetric VILI threshold and see whether PEEP is protective per se or indirectly.

METHODS:

In 76 pigs (22 ± 2 kg), we examined the lower and upper limits (30.9-59.7 mL/kg) of inspiratory capacity by computed tomography (CT) scan at 45 cmH2O pressure. The pigs underwent a 54-h mechanical ventilation with a global strain ((tidal volume (dynamic) + PEEP volume (static))/functional residual capacity) from 0.45 to 5.56. The dynamic strain ranged from 18 to 100 % of global strain. Twenty-nine pigs were ventilated with end-inspiratory volumes below the lower limit of inspiratory capacity (group "Below"), 38 within (group "Within"), and 9 above (group "Above"). VILI was defined as death and/or increased lung weight.

RESULTS:

"Below" pigs did not develop VILI; "Within" pigs developed lung edema, and 52 % died before the end of the experiment. The amount of edema was significantly related to dynamic strain (edema 188-153 × dynamic strain, R (2) = 0.48, p < 0.0001). In the "Above" group, 66 % of the pigs rapidly died but lung weight did not increase significantly. In pigs ventilated with similar tidal volume adding PEEP significantly increased mortality.

CONCLUSIONS:

The threshold for VILI is the lower limit of inspiratory capacity. Below this threshold, VILI does not occur. Within these limits, severe/lethal VILI occurs depending on the dynamic component. Above inspiratory capacity stress at rupture may occur. In healthy lungs, PEEP is protective only if associated with a reduced tidal volume; otherwise, it has no effect or is harmful.

• Authors: Alessandro Protti, Davide T Andreis, Marta Milesi, Giacomo E Iapichino, Massimo Monti, Beatrice Comini, Paola Pugni, Valentina Melis, Alessandro Santini, Daniele Dondossola, Stefano Gatti, Luciano Lombardi, Emiliano Votta, Eleonora Carlesso, Luciano Gattinoni
• Journal: Intensive care medicine experimental (Intensive Care Med Exp) Vol. 3 Issue 1 Pg. 34 (Dec 2015) ISSN: 2197-425X [Print] Germany
• PMID: 26671060 (Publication Type: Journal Article)