RESPECTIVE ROLE OF TIDAL VOLUME AND PEEP ON GLOBAL AND REGIONAL OPENING CLOSING IN ALI/ARDS

INTRODUCTION. Repeated opening and closing (O/C) of unstable alveoli in ALI/ARDS patients can induce ventilator induced lung injury. We analyze the role of both tidal volume (Vt) and positive end-expiratory pressure (PEEP) in producing atelectrauma, assessed by CT-scan. METHODS. Observational CTscan study in ten patients with ALI/ARDS. Single CT slices were taken during inspiratory and expiratory pauses with Vt 6 and 10 ml/kg at PEEP 10, 5, 15 and 20 cmH2O. Non-aerated tissue (NAT) was measured by Maluna®. Global O/C was calculated for each PEEP/Vt combination as (NAT weight/Total weight at expiration)-(NAT weight/Total weight at inspiration). Regional O/C was evaluated splitting CT slices in ten compartments in the sterno-vertebral axis. RESULTS. At Vt 6, increasing PEEP levels decrease O/C, reaching significance at PEEP 20 (2.2±2.7% vs 6.1±5.8% at PEEP 5, p<0.03). At both PEEP 5 and 15, higher Vt did not increase global O/C. Regional O/C, at PEEP 5 and Vt 6, increased from ventral to middle levels (reaching 10±12.5% at level 7, p<0.04 vs level 1), and then decreased at posterior levels (Figure). Increasing PEEP up to 20, regional O/C decreased in middle zones (p<0.02 for level 6 vs PEEP 5). Increasing Vt from 6 to 10, at PEEP 5, regional O/C persisted higher in CT middle zones and at PEEP 15, regional O/C decreased in middle zones, but significantly increased in dorsal zones. CONCLUSION. Global O/C is higher at lower PEEP levels. Regional O/C at PEEP 5 is higher in middle CT zones and can be reversed at higher PEEP levels. High Vt associated with PEEP 15 induced higher O/C at more dependent zones.