Static Pressure-Volume (P-V) Loops of the Respiratory System in Surfactant-Treated Immature Lambs in vivo - Effect of Positive End-Expiratory Pressure (PEEP) 1679

Static inspiratory P-V curves are typically S-shaped with a lower(LIP) and upper inflection point (UIP), probably because of successive recruitment of lung units. It is often said that PEEP should be above LIP to avoid derecruitment during expiration. However, the effect of PEEP on lung volume is determined by the expiratory part of the P-V loop, which has a markedly different shape. Twelve lambs with gestational age 119 to 141 days were given surfactant and were then mechanically ventilated for 2 h. Using an interrupter technique, static P-V loops were recorded between end-expiratory pressures of zero or 5 cm H₂O and an end-inspiratory pressure of 35 cm H₂O. In loops from zero pressure, LIP was at 15-20 cm H₂O, while UIP was above 30 cm H₂O, if seen at all. The expiratory limbs showed a high deflation stability, with a steep segment at low pressures, and consequently loops had a large hysteresis. Loops from 5 cm H₂O had a nearly linear inspiratory limb and a much smaller hysteresis. We conclude that in preterm newborns with adequate surfactant function and undamaged lungs, derecruitment can be avoided at much lower PEEP than is indicated by LIP. The Figure shows loops at 15 min of age in a 119 days GA lamb, weighing 2.5 kg.

Figure 1