LAUSR

BACKGROUND Variable ventilation recruits alveoli in atelectatic lungs, but it is unknown how it compares with conventional recruitment manoeuvres. OBJECTIVES To test whether mechanical ventilation with variable tidal volumes and conventional recruitment manoeuvres have comparable effects on lung function. DESIGN Randomised crossover study. SETTING University hospital research facility. ANIMALS Eleven juvenile mechanically ventilated pigs with atelectasis created by saline lung lavage. INTERVENTIONS Lung recruitment was performed using two strategies, both with an individualised optimal positive-end expiratory pressure (PEEP) associated with the best respiratory system elastance during a decremental PEEP trial: conventional recruitment manoeuvres (stepwise increase of PEEP) in pressure-controlled mode) followed by 50 min of volume-controlled ventilation (VCV) with constant tidal volume, and variable ventilation, consisting of 50 min of VCV with random variation in tidal volume. MAIN OUTCOME MEASURES Before and 50 min after each recruitment manoeuvre strategy, lung aeration was assessed by computed tomography, and relative lung perfusion and ventilation (0% = dorsal, 100% = ventral) were determined by electrical impedance tomography. RESULTS After 50 min, variable ventilation and stepwise recruitment manoeuvres decreased the relative mass of poorly and nonaerated lung tissue (percent lung mass: 35.3 ± 6.2 versus 34.2 ± 6.6, P = 0.303); reduced poorly aerated lung mass compared with baseline (−3.5 ± 4.0%, P = 0.016, and −5.2 ± 2.8%, P < 0.001, respectively), and reduced nonaerated lung mass compared with baseline (−7.2 ± 2.5%, P < 0.001; and −4.7 ± 2.8%, P < 0.001 respectively), while the distribution of relative perfusion was barely affected (variable ventilation: −0.8 ± 1.1%, P = 0.044; stepwise recruitment manoeuvres: −0.4 ± 0.9%, P = 0.167). Compared with baseline, variable ventilation and stepwise recruitment manoeuvres increased PaO2 (172 ± 85mmHg, P = 0.001; and 213 ± 73 mmHg, P < 0.001, respectively), reduced PaCO2 (−9.6 ± 8.1 mmHg, P = 0.003; and −6.7 ± 4.6 mmHg, P < 0.001, respectively), and decreased elastance (−11.4 ± 6.3 cmH2O, P < 0.001; and −14.1 ± 3.3 cmH2O, P < 0.001, respectively). Mean arterial pressure decreased during stepwise recruitment manoeuvres (−24 ± 8 mmHg, P = 0.006), but not variable ventilation. CONCLUSION In this model of lung atelectasis, variable ventilation and stepwise recruitment manoeuvres effectively recruited lungs, but only variable ventilation did not adversely affect haemodynamics. TRIAL REGISTRATION This study was registered and approved by Landesdirektion Dresden, Germany (DD24-5131/354/64).