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Strain threshold for ventilator-induced lung injury
Critical Carevolume 15, Article number: P198 (2011)
Unphysiological lung strain (tidal volume/functional residual capacity, TV/FRC) may cause ventilator-induced lung injury (VILI) . Whether VILI develops proportionally to the applied strain or only above a critical threshold remains unknown.
In 20 healthy, mechanically ventilated pigs, FRC and lung weight were measured by computed tomography. Animals were then ventilated for up to 54 hours with a TV set to produce a predetermined strain. At the end, lung weight was measured with a balance. VILI was defined as final lung weight exceeding the initial one.
Lung weight either did not increase at all (no-VILI group; lung weight change -73 ± 42 g, n = 9) or markedly augmented (VILI group; 264 ± 80 g, n = 11). In the two groups, strain was 1.38 ± 0.68 and 2.16 ± 0.50 (P < 0.01), respectively. VILI occurred only when lung strain reached or exceeded a critical threshold, between 1.5 and 2.1 (Figure 1).
In animals with healthy lungs VILI only occurs when lung strain exceeds a critical threshold.
Gattinoni L, Carlesso E, Cadringher P, et al.: Physical and biological triggers of ventilator-induced lung injury and its prevention [review]. Eur Respir J 2003,22(Suppl 47):15s-25s.