Comparison of lung area by chest radiograph, with estimation of lung volume by helium dilution during prone and supine positioning in mechanically ventilated preterm infants: A pilot study

Abstract

Measurement of lung volume may be useful in determining the degree of lung disease and for optimizing an infant's mechanical ventilator settings. A chest radiograph (CXR) is often used to estimate lung volume, because direct measurement, e.g., functional residual capacity (FRC), is neither practical nor possible in the neonatal intensive care unit. In supinely positioned infants, good correlation was found between lung area determined by CXR and lung volume, e.g., functional residual capacity (FRC). Whether this is true for the prone position is unknown. Since positioning may affect oxygenation and pulmonary function, we studied the relationship between lung area measured from CXR and FRC during both supine and prone positioning in 14 mechanically ventilated preterm infants. Lung area was determined from CXRs using computed radiography and FRCs obtained by helium dilution at end-expiration in both supine and prone positions. Reproducibility of lung area measurements was demonstrated by high correlations between two observers (R2 = 0.92 and 0.99 for supine and prone, respectively). When supine, lung area was 15.4 +/- 3.1 cm2, and FRC was 19.5 +/- 7.3 ml. In prone position, lung area was 16.7 +/- 4.2 cm2, and FRC 23.0 +/- 9.4 ml. There was a moderate to strong positive correlation between lung area and FRC for both positions (supine: r = 0.57, P < 0.03; prone: r = 0.63, P < 0.02). Lung area measured by computed radiography is a reproducible and practical method for estimating lung volume from routine chest X-rays in both supine and prone positions in mechanically ventilated preterm infants.

Placing preterm infants for sleep: first prone, then supine

“…Using sophisticated equipment for pulmonary function testing and a pulse oximeter, Kassim et al 15 confirm previous work suggesting that the prone position is associated with a higher lung volume and a better ventilation/perfusion matching 3 5. This is why these infants are nursed predominantly in the prone position in neonatal intensive care units (NICUs) throughout the world, and there is no reason to change this practice, particularly as SIDS is not an issue in these infants during their first few weeks of life in the NICU.…”

“…These epidemiological data contrast with the fact that infants who are born prematurely exhibit less apnoea and intermittent hypoxia, have better thoracoabdominal synchrony, higher lung volumes and better oxygenation when nursed in the prone position, which is particularly true for those with chronic lung disease 3 – 11. Once the infants are nearing discharge, however, these physiological advantages of the prone position become less clear 12.…”

Chest radiograph thoracic areas and lung volumes in infants developing bronchopulmonary dysplasia

“…18 In addition, a moderate to strong positive correlation between the CXR lung area and FRC assessed by helium dilution was demonstrated in 14 preterm ventilated infants in both the prone and supine positions. 19 Using a gas dilution technique, however, lung volumes can be under-recorded, as suboptimal gas diffusion occurs in lung units with a long time constant due to an elevated resistance. Under-recording can be avoided if a protocol is used which stipulates that the measurement continues until there is no change in the helium concentration, as this will allow equilibration of the helium even in areas of the lung with long time constants.…”

Tools to assess lung aeration in neonates with respiratory distress syndrome

“…There is large breath-to-breath variability in end-expiratory lung volume in premature infants with and without RDS Helium gas dilution Kumar (2005) 71 Correlation between functional residual capacity measured by chest X-ray and helium dilution 14 Functional residual capacity measured by chest X-ray is moderately correlated to functional residual capacity measured by helium dilution 38,50 Therefore, lung ultrasound may not be useful in determining successful surfactant replacement therapy, which may limit its implementation into clinical practice.…”