Variable ventilation improves ventilation and lung compliance in preterm lambs

Abstract

Variable ventilation improves ventilation efficiency and in vivo lung compliance in the preterm lung, but unlike adult models, had no effect on arterial oxygenation.

Variable ventilation enhances ventilation without exacerbating injury in preterm lambs with respiratory distress syndrome

“…The early improvement in lung elastance (reflected in reduced peak inspiratory pressures and increased compliance) and lower wet:dry ratio may be important for a preterm infant with respiratory distress syndrome and requires further assessment in a longerduration study. Similar to the findings of our earlier study (6) and despite improved lung compliance, we again did not observe a translation to improved arterial oxygenation. Oxygenation deteriorated in both ventilated groups toward the end of our study, reflecting the significant immaturity of the cardiorespiratory system.…”

“…Atelectatrauma and volutrauma are major contributors to inflammation and lung injury arising from ventilation of the surfactant-deficient, immature preterm lung that is unsupported by a highly compliant chest wall. Our measurements of lower tissue elastance in the VV group suggest that lung volume improved over time in the VV group, particularly over the first 100 min of the study, further supporting our earlier observations (6). Although the important role of sustained cyclic volutrauma in the initiation of lung injury is evident, our findings of no increase in injury in the VV group as compared with CV animals suggests that intermittent moderate increased V T may provide physiological benefit without increasing injury.…”

“…Of note, the trends toward lower elastance and higher ventilatory efficiency index emerged as early as 20 min after the initiation of ventilation despite equivalence of cord blood gases. A similar rapid improvement in lung compliance was observed within 25 min of commencing VV in an earlier study in preterm lambs (6). Together, these findings suggest that retention of variability in V T and RR is an important consideration during acute ventilation of the preterm lung during the immediate postnatal transition period.…”

“…In adult animal models, VV improves oxygenation and enhances gas exchange as compared with controlled conventional mechanical ventilation (CV) (3)(4)(5). Recently, we showed that VV enhanced both respiratory mechanics and gas exchange in preterm lambs as compared with CV that tightly regulated both breath size and rate (6), similar to findings of studies in adult animal models. However, unlike the adult animal studies, VV did not improve oxygenation in the preterm lambs, most likely due to shunting across fetal channels.…”

“…Although there was no evidence of increased lung inflammation or injury markers in our initial preterm lamb study (6), the experiment was designed to compare physiological outcomes for animals receiving constant and equivalent breath-to-breath minute volumes over the experimental period. The superior gas exchange efficiency of VV as compared with CV masked our ability to discriminate between the strategies with respect to lung injury due to hypoventilation in the CV group (6). In this study, we aimed to establish whether VV achieved physiological benefit without increasing evidence of ventilation-induced lung injury (VILI), using a strategy in which V T was adjusted to target clinically accepted ranges for gas exchange.…”