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 (P-aw), flow (F), and volume (V) were fitted by a linear single compartment model (LSCM) P-aw(t) = E-rs x V(t) + R-rs x F(t) + PEEP or a volume-and flow-dependent SCM (VFDSCM) P-aw(t) = (E-1 + E-2 x V(t)) x V(t) + (K-1 + K-2 x vertical bar F(t)vertical bar) x F(t) + PEEP, where E-rs and R-rs are respiratory system elastance and resistance, respectively; E-1 and E(2)xV are volume-independent and volume-dependent E-rs, respectively; and K-1 and K-2 x F are flow-independent and flow-dependent Rrs, respectively. Animals were ventilated for 1 h at PEEP 0 cmH(2)O (ZEEP); PEEPminErs; 2 cmH(2)O above PEEPminErs (PEEPminErs+2); or 4 cmH(2)O above PEEPminErs (PEEPminErs+4). Alveolar tidal recruitment/derecruitment and overdistension were assessed by the index % E-2 = 100 x [(E-2 x V-T)/(E-1 + vertical bar E-2 vertical bar x V-T)], and alveolar stability by the slope of E-rs(t). Results % E-2 varied between 0 and 30% at PEEPminErs in most respiratory cycles. Alveolar Tidal recruitment/derecruitment (% E-2 < 0) and overdistension (% E-2 > 30) were predominant in the absence of PEEP and in PEEP levels higher than PEEPminErs, respectively. The slope of E-rs(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-V-T mechanical ventilation.