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 (PEEP minErs ) 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 × V ( t ) + R rs × F ( t ) + PEEP or a volume- and flow-dependent SCM (VFDSCM) P aw ( t ) = ( E 1 + E 2 × V ( t )) × V ( t ) + ( K 1 + K 2 × | F ( t )|) × F ( t ) + PEEP, where E rs and R rs are respiratory system elastance and resistance, respectively; E 1 and E 2 × V are volume-independent and volume-dependent E rs , respectively; and K 1 and K 2 × F are flow-independent and flow-dependent R rs , respectively. Animals were ventilated for 1 h at PEEP 0 cmH 2 O (ZEEP); PEEP minErs ; 2 cmH 2 O above PEEP minErs (PEEP minErs+2 ); or 4 cmH 2 O above PEEP minErs (PEEP minErs+4 ). Alveolar tidal recruitment/derecruitment and overdistension were assessed by the index % E 2 = 100 × [( E 2 × V T )/( E 1 + | E 2 | × V T )], and alveolar stability by the slope of E rs ( t ). Results % E 2 varied between 0 and 30% at PEEP minErs 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 PEEP minErs , respectively. The slope of E rs (t) was different from zero in all groups besides PEEP minErs+4 . Conclusions PEEP minErs presented the best compromise between alveolar tidal recruitment/derecruitment and overdistension, during 1 h of low- V T mechanical ventilation.