A radiographic method for estimating lung volumes in sick infants

Point-of-Care Ultrasound versus Chest X-Ray for Determining Lung Expansion Based on Rib Count in High-Frequency Oscillatory Ventilation

INTRODUCTION

Chest X-ray (CXR) is the most prevalent method for evaluating lung expansion in high-frequency oscillatory ventilation (HFOV). The purpose of this study was to compare the accuracy of chest radiography with point-of-care ultrasound (POCUS) in determining lung expansion.

METHODS

This prospective study included newborns who required HFOV and were monitored in a neonatal intensive care unit. A single neonatologist assessed lung expansion with CXR and POCUS to measure the costal level of the right hemidiaphragm and compared the results.

RESULTS

A neonatologist performed 55 measurements in 28 newborns with a gestational age of 32 (23.2-39.4) weeks, followed by HFOV. The rib counts obtained from anterior chest ultrasonography and posterior CXR showed a statistically high concordance (r = 0.913, p < 0.001).

CONCLUSION

Lung ultrasonography is a reliable method for the evaluation of lung expansion based on rib count in patients with HFOV.

Quantifying lung and diaphragm morphology using radiographs in normative pediatric subjects, and predicting CT-derived lung volume

OBJECTIVE

To quantify the effect of age on two-dimensional (2D) radiographic lung and diaphragm morphology and determine if 2D radiographic lung measurements can be used to estimate computer tomography (CT)-derived lung volume in normative pediatric subjects.

MATERIALS AND METHODS

Digitally reconstructed radiographs (DRRs) were created using retrospective chest CT scans from 77 pediatric male and female subjects aged birth to 19 years. 2D lung and diaphragm measurements were made on the DRRs using custom MATLAB code, and Spearman correlations and exponential regression equations were used to relate 2D measurements with age. In addition, 3D lung volumes were segmented using CT scans, and power regression equations were fitted to predict each lung's CT-derived volume from 2D lung measurements. The coefficient of determination (R² ) and standard error of the estimate (SEE) were used to assess the precision of the predictive equations with p < .05 indicating statistical significance.

RESULTS

All 2D radiographic lung and diaphragm measurements showed statistically significant positive correlations with age (p < .01), including lung major axis (Spearman rho ≥  0.90). Precise estimations of CT-derived lung volumes can be made using 2D lung measurements (R²  ≥ 0.95), including lung major axis (R²  ≥ 0.97).

INTERPRETATIONS

The reported pediatric age-specific reference data on 2D lung and diaphragm morphology and growth rates could be clinically used to identify lung and diaphragm pathologies during chest X-ray evaluations. The simple, precise, and clinically adaptable radiographic method for estimating CT-derived lung volumes may be used when pulmonary function tests are not readily available or difficult to perform.

Correlation of radiographic thoracic area and oxygenation impairment in bronchopulmonary dysplasia

We hypothesized that radiographically-assessed hyperinflation in bronchopulmonary dysplasia (BPD) is related to the degree of oxygenation impairment. Our objective was to explore the relation of chest radiographic thoracic area (CRTA) with right-to-left shunt, right shift of the oxyhemoglobin dissociation curve and ventilation/perfusion ratio (VA/Q) in infants with BPD. Twenty-two infants born at median (IQR) gestation of 26 (24-28) weeks with BPD were prospectively studied at 39 (30-69) days. Inspired oxygen (FiO2) was varied to obtain transcutaneous oxygen saturation (SpO2) values between 85 and 96%. Shunt, shift and VA/Q were derived by plotting and analysing pairs of SpO2 and FiO2. CRTA was measured by free hand-tracing the perimeter of the thoracic area in anterio-posterior chest radiographs. Median (IQR) shunt was 8 (1-14)%, shift was 13 (11-19)kPa and VA/Q 0.42 (0.30-0.48). Median (IQR) CRTA/kg was 2495 (1962-2838)mm(2) and was significantly related to shift (r=0.674, p<0.001), VA/Q (r=-0.633, p<0.001), weight at study (r=-0.457, p=0.003) and day of life (r=-0.406, p=0.009), but not to shunt. CRTA in BPD is significantly related to oxygenation impairment as quantified by shift and VA/Q. CRTA can be used as a simple radiographic test to quantify BPD severity.

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

OBJECTIVES

To determine whether chest radiograph (CXR) thoracic areas and lung volumes differed between infants who did and did not develop BPD and according to the severity of BPD developed.

WORKING HYPOTHESIS

Infants developing BPD, particularly if moderate or severe, would have low CXR thoracic areas and lung volumes in the perinatal period.

STUDY DESIGN

Prospective study. PATIENT-SUBJECT SELECTION: 53 infants with a median gestational age of 28 (range 24-32) weeks.

METHODOLOGY

CXR thoracic areas were calculated using a Picture Archiving and Communicating System (PACS) and lung volume assessed by measurement of functional residual capacity (FRC) in the first 72 hr after birth. BPD was diagnosed if the infants were oxygen dependent beyond 28 days, mild BPD in infants no longer oxygen dependent at 36 weeks post-menstrual age (PMA) and moderate/severe BPD in infants who required supplementary oxygen with or without respiratory support at 36 weeks PMA.

RESULTS

Thirty two infants developed BPD, 21 had moderate/severe BPD. The median CXR thoracic areas were higher (P < 0.0001) and FRCs were lower (P < 0.0001) in the BPD compared to no BPD infants. The median CXR thoracic areas of the moderate/severe group (P < 0.001) and the mild group (P < 0.05) were greater than that of the no BPD group and the median FRC of the moderate/severe BPD group was lower than the no BPD group (<0.001) and the mild BPD group (P < 0.05).

CONCLUSION

These results highlight that in the perinatal period infants developing BPD, particularly if moderate/severe, have low functional lung volumes and may have gas trapping, which likely reflects ventilation inhomogeneity.

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

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.

Monitoring early inflammation in CF. Infant pulmonary function testing

Infant pulmonary function tests (iPFTs) have primarily been used as research tools to further define physiologic pulmonary abnormalities in infants and young children with cystic fibrosis (CF). Methodologies used to measure pulmonary function in infants are described, with particular relevance to CF. A comprehensive review of studies and findings in CF infants using iPFTs is presented. Further goals in improving methodologies and in defining pulmonary disease in CF are presented.

Detecting lung overdistention in newborns treated with high-frequency oscillatory ventilation

Positive airway pressure (Paw) during high-frequency oscillatory ventilation (HFOV) increases lung volume and can lead to lung overdistention with potentially serious adverse effects. To date, no method is available to monitor changes in lung volume (DeltaVL) in HFOV-treated infants to avoid overdistention. In five newborn piglets (6-15 days old, 2.2-4.2 kg), we investigated the use of direct current-coupled respiratory inductive plethysmography (RIP) for this purpose by evaluating it against whole body plethysmography. Animals were instrumented, fitted with RIP bands, paralyzed, sedated, and placed in the plethysmograph. RIP and plethysmography were simultaneously calibrated, and HFOV was instituted at varying Paw settings before (6-14 cmH(2)O) and after (10-24 cmH(2)O) repeated warm saline lung lavage to induce experimental surfactant deficiency. Estimates of Delta VL from both methods were in good agreement, both transiently and in the steady state. Maximal changes in lung volume (Delta VL(max)) from all piglets were highly correlated with Delta VL measured by RIP (in ml) = 1.01 x changes measured by whole body plethysmography - 0.35; r(2) = 0.95. Accuracy of RIP was unchanged after lavage. Effective respiratory system compliance (Ceff) decreased after lavage, yet it exhibited similar sigmoidal dependence on Delta VL(max) pre- and postlavage. A decrease in Ceff (relative to the previous Paw setting) as Delta VL(max) was methodically increased from low to high Paw provided a quantitative method for detecting lung overdistention. We conclude that RIP offers a noninvasive and clinically applicable method for accurately estimating lung recruitment during HFOV. Consequently, RIP allows the detection of lung overdistention and selection of optimal HFOV from derived Ceff data.

Measuring lung function in infancy

Although the earliest reliable lung function tests in infants were performed as long as 40 years ago, there has only recently been a growth in this area, as simpler methods and better equipment and IT resources have been developed. Exciting information is accumulating about the normal physiology and pathology of the infant lung. Many basic questions are still unanswered and the ability to perform these tests remains confined to a few specialized centres. To co-ordinate the development of ILFT and establish standardization in a number of areas including measurement conditions, equipment specifications, methodology protocols and data analysis, international collaboration is necessary between the teams working in this field (Table 5). Collaborative groups are currently addressing these issues and are also developing recommendations regarding the design of randomized clinical trials, multi-centre studies and research agendas. Infant lung function testing remains primarily a research tool. Our aim should be not only to refine and develop the techniques of physiological measurement but to apply ILFT to the objective study of respiratory illness in infants in the clinical setting so as to aid in the prevention and treatment of these common, debilitating and costly diseases.

Measuring pulmonary function in infancy

In recent years there has been a growing interest in the measurement of pulmonary function in infants for both clinical and research purposes. Such measurements remain limited by the complexity of the equipment as well as by the technical and physiological challenges of testing infants and neonates. Despite these problems, assessment of respiratory function in early life provides exciting information about the post-natal growth and development of lungs in health and disease. The aim of this paper is to discuss the physiological, technical and ethical problems surrounding these procedures, as well as reviewing the current methods of testing pulmonary function in the very young. Consideration is given to the developments needed if infant pulmonary function tests are to realise fully, their potential as research and clinical tools.

Computer assisted analysis of the chest radiograph lung area and prediction of failure of extubation from mechanical ventilation in preterm neonates

Post-extubation chest radiographs (CXRs) are frequently requested on the neonatal intensive care unit, but it is controversial whether they generate useful information. A low lung volume assessed by measurement of functional residual capacity (FRC) post extubation has been demonstrated to predict extubation failure, which is a subsequent requirement for increased respiratory support. We have previously shown that the CXR lung area obtained by computer assisted analysis significantly correlated with FRC and, therefore, speculated that a low CXR lung area post extubation would reliably predict extubation failure. The aim of this study was to test the hypothesis by analysing CXRs from 20 infants, with median gestational age of 28 weeks (range 25-33 weeks) and postnatal age 4 days (range 1-11 days). CXRs were obtained within 4 h of extubation and were scanned and analysed using a Power Macintosh computer with a Wacom A5 Ultra pad and NIH image software. The cardiac, mediastinal and thymic shadows, and areas of perihilar and lobar consolidation were subtracted from the thoracic area to give the lung area. Seven infants failed extubation and differed significantly from the rest of the cohort only with regard to their CXR lung area, median gestational age, birth weight and postnatal age. Receiver operator characteristic (ROC) curves were constructed and the areas under each ROC curve were compared. Analysis demonstrated that a low CXR lung area and an older postnatal age were the best predictors of extubation failure. A post-extubation CXR lung area of < 8.5 cm2 had the highest specificity (100%) in predicting extubation failure. We conclude that routine post-extubation CXRs can have a useful role.

Estimation of gas and tissue lung volumes by MRI: functional approach of lung imaging

PURPOSE

The purpose of this work was to assess the accuracy of MRI for the determination of lung gas and tissue volumes.

METHOD

Fifteen healthy subjects underwent MRI of the thorax and pulmonary function tests [vital capacity (VC) and total lung capacity (TLC)] in the supine position. MR examinations were performed at inspiration and expiration. Lung volumes were measured by a previously validated technique on phantoms. Both individual and total lung volumes and capacities were calculated. MRI total vital capacity (VC(MRI)) was compared with spirometric vital capacity (VC(SP)). Capacities were correlated to lung volumes. Tissue volume (V(T)) was estimated as the difference between the total lung volume at full inspiration and the TLC.

RESULTS

No significant difference was seen between VC(MRI) and VC(SP). Individual capacities were well correlated (r = 0.9) to static volume at full inspiration. The V(T) was estimated to be 836+/-393 ml.

CONCLUSION

This preliminary study demonstrates that MRI can accurately estimate lung gas and tissue volumes. The proposed approach appears well suited for functional imaging of the lung.

A radiographic method for assessing lung area in neonates

The aim of this study was to determine whether computer assisted analysis of lung area on the chest radiograph reliably predicted lung volume in neonates. Anteroposterior chest radiographs taken for clinical purposes were scanned and analysed using a Power Macintosh computer with a Wacom A5 Ultra Pad and NIH image software. The cardiac, mediastinal and thymic densities and areas of perihilar and lobar consolidation were subtracted from the thoracic area to give the lung area. This was compared with lung volume, assessed by measurement of functional residual capacity (FRC), within 1 h of the chest radiograph being performed. 50 infants, median gestational age 30 weeks (range 24-43) were studied. Their median lung area was 11.23 cm2 (range 0.82-28.53) and lung volume 28 ml (range 3-103). The intraobserver and interobserver coefficients of repeatability of lung area were 1.0 cm2 and 1.06 cm2, respectively. Lung area correlated significantly with FRC (r = 0.60, p < 0.0001). It is concluded that computer assisted analysis of the chest radiograph lung area is a reliable method of assessing lung volume in neonates.

Comparison of lung volume measurements by antero-posterior chest X-ray and the SF6 washout technique in mechanically ventilated infants

While anterior/posterior chest x-rays (CXR) are routinely performed to estimate lung volume (LV) and adjust ventilator settings, the precise measurement of LV requires additional sophistication. In 31 infants ventilated because of surfactant deficiency (n=23), bronchopulmonary dysplasia (n=7), or pulmonary hypoplasia (n=1) with either intermittent positive pressure (n=18) or high frequency oscillation (n=13) (gestational age 23-39 weeks (median 26 weeks); birthweight 550-2780 g (median 840 g); age at measurement 1-91 days (median 6 days); weight at study time (WST) 675-3000 g (median 938 g)), we investigated whether LV, as measured by the sulfur hexafluoride (SF6) washout technique, could by estimated from CXR by: 1) the sum (A+B) of the right (A) and left (B) lung fields areas; 2) the product (LxW) of the distances from the right apex to the right costophrenic angle (L) and between both costophrenic angles (W); 3) the diaphragm position relative to the posterior parts of the ribs (DP); and 4) the lung radiolucency (RL, grades 0-4). Correlations between A+B (r=0.44) or LxW (r=0.37) and LV were poor, but improved when A+B, LxW, and LV were normalized to WST: (A+B)/WST vs. LV/WST (r=0.74), and LxW/WST vs. LV/WST (r=0.67). DP (r=0.13) and RL (Spearman's rho=0.17) did not correlate with LV/WST. A multiple linear regression analysis led to the following best-fit equation: LV/WST=2.58 (A+B)/WST - 5.47 DP + 42.2 (r=0.83). We concluded that an estimate of LV from CXR lacked sufficient accuracy. DP and RL did not correlate with LV measured by SF6 washout.

Randomized trial of long-term diuretic therapy for infants with oxygen-dependent bronchopulmonary dysplasia

STUDY OBJECTIVE

To determine whether long-term oral diuretic therapy would improve the pulmonary function of preterm infants with bronchopulmonary dysplasia.

DESIGN

Randomized, double-blind, placebo-controlled study.

SETTING

Level III intensive care nursery.

INTERVENTION

We randomly selected 43 stable patients with oxygen-dependent bronchopulmonary dysplasia to receive either orally administered spironolactone and chlorothiazide or placebo. These drugs were continued until the patients no longer required supplemental oxygen. Both groups received furosemide as needed.

MEASUREMENTS AND RESULTS

Each infant had pulmonary function tests at study entry, 4 weeks after study entry, 1 week and 8 weeks after being weaned to room air and off study drugs, and at 1 year of corrected age. Pulmonary function tests include dynamic pulmonary compliance, airway resistance, thoracic gas volume, and maximal expiratory flow at functional residual capacity; most of the infants had functional residual capacity measured. Between the first and second pulmonary function tests (while the infants were receiving diuretic or placebo), the infants in the diuretic group had a significant improvement in dynamic pulmonary compliance (46%; p < 0.001) and airway resistance (31%; p < 0.05); there were no changes in compliance or resistance in the placebo group. Although patients in both the diuretic and the placebo groups required progressively less supplemental oxygen, by 4 weeks after study entry the patients in the diuretic group needed less supplemental oxygen than did those in the placebo group (p < 0.01). There were no significant differences in results of serial pulmonary function tests in either group after discontinuation of diuretic therapy. Despite the significant differences in pulmonary function between the two groups, there was no significant difference between them in the total number of days that supplemental oxygen was required. Significantly more infantsin the placebo group received more than 10 doses of furosemide on an as-needed basis.

CONCLUSIONS

Long-term diuretic therapy in stable infants with oxygen-dependent bronchopulmonary dysplasia, after extubation, improves their pulmonary function and decreases their fractional inspired oxygen requirement, but does not decrease the number of days that they require supplemental oxygen. The improvement in pulmonary function associated with diuretic therapy is not maintained after treatment is discontinued.