Establishing lung gas volumes at birth: interaction between positive end-expiratory pressures and tidal volumes in preterm rabbits

Abstract

Background:We investigated the effects of positive endexpiratory pressure (PEEP) and tidal volume (V T ) on lung aeration, pulmonary mechanics, and the distribution of ventilation immediately after birth using a preterm rabbit model. Methods: Sixty preterm rabbits (27 d) received volumetargeted positive pressure ventilation from birth, with one of the 12 combinations of PEEP (0, 5, 8, or 10 cmH 2 O) and V T (4, 8, or 12 ml/kg). Outcomes included functional residual capacity (FRC), peak inflating pressure (PIP), dynamic compliance (Cd), and distribution of ventilation. results: Increasing PEEP from 0 to 10 cmH 2 O increased FRC by 4 ml/kg, increased Cd by 0.2 ml/kg/cmH 2 O, and reduced PIP by 5 cmH 2 O. Increasing V T from 4 to 12 ml/kg increased FRC by 2 ml/kg, increased Cd by 0.3 ml/kg/cmH 2 O, and increased PIP by 4 cmH 2 O. No effect of V T on FRC occurred at 0 or 5 PEEP, and no effect of PEEP occurred at V T = 4 ml/kg. At 0 PEEP, increasing V T increased the proportion of gas entering the smaller apical regions, whereas at 10 PEEP, increasing V T increased the proportion of gas entering basal regions, from 47% to 63%. conclusion: Both PEEP and V T have independent, additive effects on FRC, lung mechanics, and the distribution of ventilation during the immediate newborn period.

Sustained inflation at birth did not protect preterm fetal sheep from lung injury

“…A SI of 10 s or greater was needed to develop FRC in neonatal rabbits (41). Physiologically, a 30-s SI improved circulatory return in asphyxiated near-term lambs, whereas a series of five 3-s SI (as suggested by the European resuscitation guidelines) did not increase heart rate over ventilation alone (21,30).…”

The interrelationship of recruitment maneuver at birth, antenatal steroids, and exogenous surfactant on compliance and oxygenation in preterm lambs

“…PEEP is essential in the preterm lung (5,14). In our study, we used a PEEP (8 cmH 2 O) previously shown to be appropriate in preterm lambs (6,11,16,17), and higher than that used in similar animal studies (5,9,10,14,15,20,29), suggesting our results are due to differences in recruitment strategy and not subsequent ventilator management.…”

“…In our study using intubated preterm lambs, we systematically describe the interrelationship between the use of antenatal corticosteroids, exogenous surfactant therapy, and two distinct recruitment strategies applied Unlike previous animal studies of respiratory care at birth (6,(10)(11)(12)15,16,(20)(21)(22)(27)(28)(29)(30), our study involved a large sample size. Pooling all epochs, the use of an OLV stepwise PEEP approach significantly improved C dyn and oxygenation compared to a 30-s 40 cmH 2 O SI.…”

“…It is feasible that the higher maximum possible inflating pressure during the OLV strategy, compared to the initial SI pressure of 40 cmH 2 O, influenced aeration (15,16). Recently, we reported the detailed analysis of the Control epoch compared to a group receiving positive pressure ventilation (PPV) at 8 cmH 2 O PEEP.…”

“…During this period, the infant must rapidly clear lung liquid, aerate the lung, establish a functional residual capacity, and commence tidal ventilation, processes influenced by the intrinsic mechanical properties of the lung as well as the applied respiratory strategy (5,6,(9)(10)(11)(12)(13). The optimal approach in preterm infants remains unclear but broadly requires an inflating pressure to drive fetal lung fluid into the alveoli and allow lung aeration, and positive end-expiratory pressure (PEEP) to maintain aeration and prevent fluid efflux back into the airways (14)(15)(16)(17). In preterm animals, using an initial stepwise PEEP or open lung ventilation (OLV) approach during tidal ventilation from birth improves aeration and short-term respiratory outcomes in preterm animals via utilizing hysteresis and time dependency (6,11).…”