Pressure- versus volume-limited sustained inflations at resuscitation of premature newborn lambs

Abstract

BackgroundSustained inflations (SI) are advocated for the rapid establishment of FRC after birth in preterm and term infants requiring resuscitation. However, the most appropriate way to deliver a SI is poorly understood. We investigated whether a volume-limited SI improved the establishment of FRC and ventilation homogeneity and reduced lung inflammation/injury compared to a pressure-limited SI.Methods131 d gestation lambs were resuscitated with either: i) pressure-limited SI (PressSI: 0-40 cmH2O over 5 s, maintained until 20 s); or ii) volume-limited SI (VolSI: 0-15 mL/kg over 5 s, maintained until 20 s). Following the SI, all lambs were ventilated using volume-controlled ventilation (7 mL/kg tidal volume) for 15 min. Lung mechanics, regional ventilation distribution (electrical impedance tomography), cerebral tissue oxygenation index (near infrared spectroscopy), arterial pressures and blood gas values were recorded regularly. Pressure-volume curves were performed in-situ post-mortem and early markers of lung injury were assessed.ResultsCompared to a pressure-limited SI, a volume-limited SI had increased pressure variability but reduced volume variability. Each SI strategy achieved similar end-inflation lung volumes and regional ventilation homogeneity. Volume-limited SI increased heart-rate and arterial pressure faster than pressure-limited SI lambs, but no differences were observed after 30 s. Volume-limited SI had increased arterial-alveolar oxygen difference due to higher FiO2 at 15 min (p = 0.01 and p = 0.02 respectively). No other inter-group differences in arterial or cerebral oxygenation, blood pressures or early markers of lung injury were evident.ConclusionWith the exception of inferior oxygenation, a sustained inflation targeting delivery to preterm lambs of 15 mL/kg volume by 5 s did not influence physiological variables or early markers of lung inflammation and injury at 15 min compared to a standard pressure-limited sustained inflation.

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.…”

“…We have recently shown that there is considerable variability in the spatiotemporal behavior of lung mechanics at birth, even in controlled preclinical experiments (6,12,23). Although our choice of SI parameters is based on previous work (9,10,12,20,27,29), it is likely that some of our lambs required a longer SI duration. Our results may reflect insufficient regional aeration, a situation clinicians currently have no bedside tools to rapidly detect during a SI.…”

“…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.…”

“…The most widely examined intentional recruitment maneuver at birth is the use of an initial sustained inflation (SI) to clear fetal lung liquid from the airways (18,19). Preclinical experimental studies of SI have been mixed (5,6,(9)(10)(11)20), with an increase in lung injury reported in some studies (21-23). Improved short-term respiratory outcomes have been reported in some clinical trials (24,25), although without long-term benefits, and an increased risk of patent ductus arteriosus (19).…”

“…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).…”