Estimating Preterm Lung Volume: A Comparison of Lung Ultrasound, Chest Radiography, and Oxygenation

Abstract

To determine the relationship between lung ultrasound (LUS), chest x-ray (CXR), radiographic and clinical evaluation in the assessment of lung volume in preterm infants STUDY DESIGN: In this prospective cohort study LUS was performed before CXR on 70 preterm infants and graded using: 1. a LUS score; 2. an atelectasis score; and 3. measurement of atelectasis depth. Radiographic diaphragm position and radio-opacification were used to determine global and regional radiographic atelectasis. The relationship between LUS, CXR, and oxygenation was assessed using receiver operator characteristics (ROC) and correlation analysis. LUS scores, atelectasis scores, and atelectasis depth did not correspond with radiographic global atelectasis (area under ROC curves [95% CI]: 0.54[0.36,0.71], 0.49[0.34,0.64], 0.47[0.31,0.64], respectively). Radiographic atelectasis of the right upper, right lower, left upper, and left lower quadrants was predicted by LUS scores (0.75[0.59,0.92], 0.75[0.62,0.89], 0.69[0.56,0.82], 0.63[0.508,0.751]) and atelectasis depth (0.66 [0.54,0.78], 0.65[0.53,0.77], 0.63[0.50,0.76], 0.56[0.44,0.70]). LUS findings were moderately correlated with oxygen saturation index (ρ=0.52[0.30,0.70]) and saturation to fraction of inspired oxygen ratio (ρ=-0.63[-0.76,-0.46]). The correlation between radiographic diaphragm position, oxygenation saturation index, and SpO2 to FiO2 ratio was very weak (ρ=0.36[0.11,0.59] and ρ=-0.32[-0.53,-0.07] respectively). LUS assessment of lung volume does not correspond with radiographic diaphragm position preterm infants. However, LUS predicted radiographic regional atelectasis and correlated with oxygenation. The relationship between radiographic diaphragm position and oxygenation was very weak. While LUS may not replace all radiographic measures of lung volume, LUS more accurately reflects respiratory status in preterm infants.