Impact of Recruitment on Static and Dynamic Lung Strain in Acute XXXX .

@entity1 @entity1707 @entity3952 @entity4358 @entity649
BACKGROUND: Lung strain, defined as the ratio between end-inspiratory volume and functional residual capacity, is a marker of the mechanical load during ventilation. However, changes in lung volumes in response to pressures may occur in injured lungs and modify strain values. The objective of this study was to clarify the role of recruitment in strain measurements. METHODS: Six @entity3952 -injured @entity1707 were ventilated at positive end-expiratory pressure (PEEP) 0 and 10 cm @entity4358 before and after a recruitment maneuver (PEEP = 20 cm @entity4358 ). Lung volumes were measured by helium dilution and inductance plethysmography. In addition, six @entity1 with moderate-to-severe acute @entity649 were ventilated with three strategies (peak inspiratory pressure/PEEP: 20/8, 32/8, and 32/20 cm @entity4358 ). Lung volumes were measured in computed tomography slices acquired at end-expiration and end-inspiration. From both series, recruited volume and lung strain (total, dynamic, and static) were computed. RESULTS: In the animal model, recruitment caused a significant decrease in dynamic strain (from [mean    SD] 0.4    0.12 to 0.25    0.07, P < 0.01), while increasing the static component. In @entity1 , total strain remained constant for the three ventilatory settings (0.35    0.1, 0.37    0.11, and 0.32    0.1, respectively). Increases in tidal volume had no significant effects. Increasing PEEP constantly decreased dynamic strain (0.35    0.1, 0.32    0.1, and 0.04+0.03, P < 0.05) and increased static strain (0, 0.06    0.06, and 0.28    0.11, P < 0.05). The changes in dynamic and total strain among @entity1 were correlated to the amount of recruited volume. An analysis restricted to the changes in normally aerated lung yielded similar results. CONCLUSION: Recruitment causes a shift from dynamic to static strain in early acute @entity649 .
