Alveolar Tidal recruitment/derecruitment and Overdistension During Four Levels of End-Expiratory Pressure with Protective Tidal Volume During Anesthesia in a Murine Lung-Healthy Model.

PURPOSE: We compared respiratory mechanics between the positive end-expiratory pressure of minimal respiratory system elastance (PEEPminErs) and three levels of PEEP during low-tidal-volume (6 mL/kg) ventilation in rats. METHODS: Twenty-four rats were anesthetized, paralyzed, and mechanically ventilated. Airway pressure (Paw), flow (F), and volume (V) were fitted by a linear single compartment model (LSCM) Paw(t) = Ers × V(t) + Rrs × F(t) + PEEP or a volume- and flow-dependent SCM (VFDSCM) Paw(t) = (E1 + E2 × V(t)) × V(t) + (K1 + K2 × |F(t)|) × F(t) + PEEP, where Ers and Rrs are respiratory system elastance and resistance, respectively; E1 and E2× V are volume-independent and volume-dependent Ers, respectively; and K1 and K2 × F are flow-independent and flow-dependent Rrs, respectively. Animals were ventilated for 1 h at PEEP 0 cmH2O (ZEEP); PEEPminErs; 2 cmH2O above PEEPminErs (PEEPminErs+2); or 4 cmH2O above PEEPminErs (PEEPminErs+4). Alveolar tidal recruitment/derecruitment and overdistension were assessed by the index %E2 = 100 × [(E2 × VT)/(E1 + |E2| × VT)], and alveolar stability by the slope of Ers(t). RESULTS: %E2 varied between 0 and 30% at PEEPminErs in most respiratory cycles. Alveolar Tidal recruitment/derecruitment (%E2 < 0) and overdistension (%E2 > 30) were predominant in the absence of PEEP and in PEEP levels higher than PEEPminErs, respectively. The slope of Ers(t) was different from zero in all groups besides PEEPminErs+4. CONCLUSIONS: PEEPminErs presented the best compromise between alveolar tidal recruitment/derecruitment and overdistension, during 1 h of low-VT mechanical ventilation.