Lung ultrasound detects regional aeration inhomogeneity in ventilated preterm lambs.

BACKGROUND: Inhomogeneous lung aeration is a significant contributor to preterm lung injury. EIT detects inhomogeneous aeration in the research setting. Whether LUS detects inhomogeneous aeration is unknown. The aim was to determine whether LUS detects regional inhomogeneity identified by EIT in preterm lambs. METHODS: LUS and EIT were simultaneously performed on mechanically ventilated preterm lambs. LUS images from non-dependent and dependent regions were acquired and reported using a validated scoring system and computer-assisted quantitative LUS greyscale analysis (Q-LUSMGV). Regional inhomogeneity was calculated by observed over predicted aeration ratio from the EIT reconstructive model. LUS scores and Q-LUSMGV were compared with EIT aeration ratios using one-way ANOVA. RESULTS: LUS was performed in 32 lambs (~125d gestation, 128 images). LUS scores were greater in upper anterior (non-dependent) compared to lower lateral (dependent) regions of the left (3.4 vs 2.9, p = 0.1) and right (3.4 vs 2.7, p < 0.0087). The left and right upper regions also had greater LUS scores compared to right lower (3.4 vs 2.7, p < 0.0087) and left lower (3.7 vs 2.9, p = 0.1). Q-LUSMGV yielded similar results. All LUS findings corresponded with EIT regional differences. CONCLUSION: LUS may have potential in measuring regional aeration, which should be further explored in human studies. IMPACT: Inhomogeneous lung aeration is an important contributor to preterm lung injury, however, tools detecting inhomogeneous aeration at the bedside are limited. Currently, the only tool clinically available to detect this is electrical impedance tomography (EIT), however, its use is largely limited to research. Lung ultrasound (LUS) may play a role in monitoring lung aeration in preterm infants, however, whether it detects inhomogeneous lung aeration is unknown. Visual LUS scores and mean greyscale image analysis using computer assisted quantitative LUS (Q-LUSMGV) detects regional lung aeration differences when compared to EIT. This suggests LUS reliably detects aeration inhomogeneity warranting further investigation in human trials.

Inflating Pressure and Not Expiratory Pressure Initiates Lung Injury at Birth in Preterm Lambs.

Rationale: Inflation is essential for aeration at birth, but current inflating pressure settings are without an evidence base. Objectives: To determine the role of inflating pressure (ΔP), and its relationship with positive end-expiratory pressure (PEEP), in initiating early lung injury pathways in the preterm lamb lung. Methods: Preterm (124 to 127 d) steroid-exposed lambs (n = 45) were randomly allocated (8-10 per group) to 15 minutes of respiratory support with placental circulation and 20 or 30 cm H2O ΔP, with an initial high PEEP (maximum, 20 cm H2O) recruitment maneuver known to facilitate aeration (dynamic PEEP), and compared with dynamic PEEP with no ΔP or 30 cm H2O ΔP and low (4 cm H2O) PEEP. Lung mechanics and aeration were measured throughout. After an additional 30 minutes of apneic placental support, lung tissue and bronchoalveolar fluid were analyzed for regional lung injury, including proteomics. Measurements and Main Results: The 30 cm H2O ΔP and dynamic PEEP strategies resulted in quicker aeration and better compliance but higher tidal volumes (often >8 ml/kg, all P < 0.0001; mixed effects) and injury. ΔP 20 cm H2O with dynamic PEEP resulted in the same lung mechanics and aeration, but less energy transmission (tidal mechanical power), as ΔP 30 cm H2O with low PEEP. Dynamic PEEP without any tidal inflations resulted in the least lung injury. Use of any tidal inflating pressures altered metabolic, coagulation and complement protein pathways within the lung. Conclusions: Inflating pressure is essential for the preterm lung at birth, but it is also the primary mediator of lung injury. Greater focus is needed on strategies that identify the safest application of pressure in the delivery room.