Comparative Study between Chest X-Ray and Lung Ultrasound in Neonatal Respiratory Distress

Acknowledgements

To all the staff members, assistant lecturers, residents and nursing team of the NICU and to every one helped to finish this study in the final form.

Author's contributions

HE, ME and HH equally contributed in the study concept, design, supervision, methodology, statistical analysis and data collection. TM performed the investigations workup and wrote the first draft of the manuscript.

Conflict of interest

Authors declare they have no conflict of interest

Fund

The manuscript funded only from the authors.

Date received: 16^th December 2020, accepted 18^th January 2021.

Methods

This prospective study has been conducted at Neonatal Intesive Care Unit (NICU) in Al-Azhar Assiut University Hospital from 1^st November 2019 to 31^th October 2020. The study was conducted to 50 neonates with moderate respiratory distress, 14 of them were females (28%) and 36 of them were males (72%). All newborns included in the study admitted to neonatal intensive care unit: 13 of them stabilized on nasal oxygen, 37 of them stabilized on Nasal Continuous Positive Airway Pressure (NCPAP) for 6 hours. 8 of them need mechanical ventilation based on clinical, arterial blood gases and lung ultrasonographic findings. Lung ultrasound was performed within 2 hours and repeated after 6 hours. Chest x-ray also was performed and scored.

Both Lung ultrasound score and chest x-ray score were used and compared for respiratory distress syndrome neonates.

Inclusion criteria: Full term and preterm neonates in a clinical setting with signs and symptoms of moderate respiratory distress diagnosed using a combination of clinical indicators (presentation, vital signs and auscultation),chest x-ray and laboratory blood gas analysis.

Exclusion criteria: Neonates presented with respiratory distress due to extra pulmonary causes e.g.: Congenital heart diseases (CHD), renal failure, and electrolyte disturbances early severe sepsis….etc.

All neonates enrolled in this study were subjected to:

Pre-natal history: pregnancy condition including (drug intake, smoking, seizures in pregnancy, hospitalization in early pregnancy, severe anemia , frequency of prenatal visits, prior fetal death, birth interval), Natal history: labour and delivery (spontaneous or induced onset of labour, duration of labour, methods of delivery, signs of fetal distress, problem during labour and delivery, medicines given to the mother e.g. pethidine and antenatal steroid ,  Post-natal history: Apgar score and any resuscitation needed, any abnormalities detected, birth weight and circumference, estimated gestational age and vitamin K given. Full clinical examination: General examination, systemic examination, chest examination. Investigations: CBC (Complete blood count), CRP (C- reactive protein), Blood gas analysis.  A Lung Ultrasound (LUS) was performed at the bedside on respiratory distressed neonates 2 hours repeated after 6 hours immediately after admission by Transthoracic approach with longitudinal scans of the anterior and posterior chest walls, A high-resolution linear probe with a frequency of more than 7.5 MHz (GE Voluson i or E 6, USA) was used and read by an independent radiologist. Chest X-Ray was performed at the bedside on respiratory distressed patients with low MA (Milliampere second) technique antero-posterior view in the supine position   just following the lung ultrasound.

Chest Radiogram was considered in order to(0-4) score for all (19) neonates with respiratory syndrome (RDS) and it was graded in both lungs as follows:[0] normal radiolucent lung fields with sharp cardiac and diaphragmatic margins [1]slightly reduced radiolucency with still sharp cardiac and diaphragmatic margins [2] markedly reduced radiolucency with retained cardiac and diaphragmatic margins [3]severely reduced radiolucency with air bronchogram and blurred cardiac and diaphragmatic margins [4]completely white lung fields with or without air bronchogram and barely visible cardiac and diaphragmatic margin. [19&20].

Chest ultrasound was considered in order to (0-3) score for all (19) neonates with respiratory syndrome (RDS) and it was graded in both lungs as follows: Lung have been divided into three areas, upper anterior, lower anterior, and lateral. For each area, a score of 0-3 has been assigned. Score values correspond to different patterns. Scores were given as follows [0] presence of only A-lines [1] presence of A-lines in the upper part of the lung and coalescent B-lines in the lower part of the lung (pattern 1a) or at least 3 B-lines (pattern 1b) [2] presence of crowded and coalescent B lines with or without consolidations limited to sub-pleural space [3] presence of extended consolidation [19&20].

Ethical consideration

Oral and written consents were taken from parents or guardians of the patients and the aim of the study was explained to the parents before collection of the data. The privacy of all data collected was assured.

Statistical analysis

The collected data were revised, organized, tabulated and statistically analyzed using statistical package for social sciences (SPSS) version 25.0 for windows. Data are presented as the Mean ± standard deviation (SD), frequency, and percentage. McNemar test and McNemar-Bowker test were used for comparison between different diagnostic methods and findings. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy of the tested findings were calculated. A 0.05 level was chosen as a level of significance in all statistical tests used in the study.

Results

During the study, 64 babies were considered eligible. 11 patients were excluded because of exclusion criteria (4 with complex malformation, 3 with congenital lung diseases and 4 with early severe sepsis) and 3 patients because consent was denied, leaving 50 in the study. The results of the present study were illustrated in the following tables and figures:  

-Table (1): Characteristics of studied neonates with moderate respiratory distress.

-Table (2): Various etiological diagnoses of the 50 neonates with moderate respiratory distress by chest x-ray and lung ultrasound.

-Table (3): Chest ultrasonography findings in 50 neonates with moderate respiratory distress.

-Table (4): Concordance of ultrasound and Radiographic Results for 19 neonates with RDS.

-Table (5):  Chest x rays versus chest ultrasonography in diagnosis of neonatal chest diseases.

-Figure(1): (A) Ultrasound picture of upper chest in RD patient shows multiple longitudinal white lines related to B lines with loss of A lines suggestive of mild interstitial lung edema (score 1). (B) Chest x-ray shows (Score 2) respiratory distress syndrome of reduce radiolucency and preserved cardiac margins.

-Figure (2): (A) Ultrasound picture of upper chest in RD patient shows white lung picture due to multiple adjacent confluent longitudinal white lines related to B lines suggestive of sever form of interstitial lung edema (Score 2). (B) Chest x-ray shows (score 3) respiratory distress syndrome of marked reduced radiolucency and blurred cardiac margins.

-Figure (3):  (A) Lung ultrasound shows a significant area of consolidation with air bronchograms in the left lung.  (B) Chest x-ray shows (score 4) respiratory distress syndrome of marked reduced radiolucency and obscured cardiac margins.

Discussion

In the present study respiratory distress syndrome (RDS) represented the highest percentage of 50 neonates with moderate respiratory distress followed by transient tachypnea of newborn (TTN) and meconium aspiration syndrome (MAS) (38%), (32%) and (10%) respectively .These findings were found to be higher than the findings of  Chen et al study. [11] on routine application of lung ultrasonography in NICU where their percentage were (19.3%), (11.4%)and (6.7%) respectively. However the reverse has been occurred in neonatal pneumonia which was the diagnosis in (17.5%) of our cases compared to (29.8%) in Chen et al study. [11] 

According to Ultrasound indexes used in this study , (Pleural line): is the regular echogenic line under the superficial layers of the thorax moving continuously during respiration, while abnormal pleural lines refer to pleural lines disappearance [13].(A-line): a series of echogenic, horizontal, parallel lines equidistant from one another below the pleural line, which are the reverberation artifacts of the pleural line [14&15].(B-lines): also known as ultrasound lung comets, hyperechoic narrow-based artifacts spreading like laser rays from the pleural line to the edge of the screen[16]. (Lung consolidation): defined as areas of hepatization with presence of air bronchograms or fluid bronchograms [15&17]. (Pleural effusion): defined as anechoic-dependent collections limited by the diaphragm and the pleura [17]. (Interstitial syndrome): defined as the presence of more than 3 B-lines or the presence of areas of ‘white lung’ in every examined area [18].( Bilateral white lung): defined as the presence of compact B-line in the 6areas without horizontal reverberation [13]. (Double lung point sign) refers to a sharp boundary found between relatively aireated superior lung fields and coalescent "B‐lines" (representing interstitial edema) in the basal lung fields, with a reported sensitivity of 45.6%-76.7% and a specificity of 94.8%-100%  in diagnosing transient tachypnea of the newborn[13&21].

In our study the total number of respiratory distress syndrome (RDS) diagnosed by Lung ultrasound  was 19 (38%), The abnormalities of the pleural line and A-line disappearance were found in 19 cases  (100%) which matches with Chen et al. [11] and Liu et al. [12] while, interstitial syndrome, was present in 4 cases (21%) which was higher than that of Chen et al. [11] (14.8%) however  lung consolidation could be found on Lung ultrasound in 18 cases (94.7%) which was less than that of  Chen et al. [11] study (100%).  Pulmonary oedema or white lung could be found on lung ultrasound in 15 cases (78.9%) which was less than that of Chen et al. [11] (85.2%).

The contradictory between our results and that of other studies might be attributed to differences of clinical severity of cases. The number of cases with RDS having pleural effusion was zero compared to that of Chen et al. [11]   (31.7%).However double lung point was not found  in our study and this matches with Chen et al. [11]

The sensitivity and specificity of combined lung consolidation, pleural line abnormalities and bilateral pulmonary edema finding by lung ultrasound in respiratory distress syndrome (RDS) was 96% and 63.3% respectively compared to 100% in studies of Liu et al.[12]  The sensitivity and specificity of combined lung consolidation, pleural line abnormalities and interstitial lung was 84.6 % and 77% respectively compared to 100% in studies of  Liu et al  [12].

Based on lung ultrasound scan after 6 hours on NCPAP, Nine neonates were assigned score 3, five to score 2, and five to score 1. Eight newborns with score 3 were intubated after an average interval of 5-7 hours. No infant with score 1 or score 2 profile was intubated. In predicting failure of NIV, score 3 lung ultrasound had the following accuracy with 71.2% sensitivity and 80% specificity.

On the basis of the chest radiograph, no infant was assigned to grade 4 or 3,whereas five neonates were assigned to grade 2 and 14 to grade 1. The accuracy of grade 2 to predict intubation was as follows: 31.2% sensitivity and 62.3% specificity.

Lung ultrasound in transient tachypnea of newborn reported pleural line abnormality and absence A line  in 16 cases (100%) which was found to be in concordance with that of Chen et al. [11]. While interstitial lung was present in 12 (75%) which was more higher than that of Chen et al. [11] (70.39%). Pulmonary oedema was present in 5 cases of TTN (31.25%) which was higher than that of Chen et al. [11] (29.7%). This disagreement might be due to the severity of the disease.  Double lung point was present in 12 cases (75%) which were higher than those found in Chen et al. [11] and their percent was. (34.1%).  Pleural effusion was not present in any case of transient tachypnea of newborn in comparison to (19.4%) in Chen et al. [11]. We found that there was significant relation between double lung point and TTN in 12 cases (75%) was statistically significant (p value <0.001) with 52% sensitivity and 100% specificity.

The total number of pneumonia of diagnosed by Lung ultrasound was 8 (16%) and this was matched with the initial diagnosis made clinically. In our study the abnormalities of the pleural line were found in 7 cases of pneumonia (87.5%) which was less than Chen et al. [11] that was (90.9%). While A-line disappearance, and lung consolidation were found in 8 cases (100%) which matches with Chen et al. [11]. Double lung point couldn't be seen in pneumonia and this matches with Chen et al. [6] study. Pleural effusion was present in one case (12.5%) which was higher than Chen et al. [11] study which was (8.7%).

All cases diagnosed initially as MAS by chest x rays, their diagnosis confirmed by chest US by the presence of lung consolidation. Pleural line abnormalities was present in 4 cases (80%) less than those detected in Liu et al[12]  which was 100% and Chen et al. [11] which was 88% .  Lung consolidation and absence of A line were present in (100%) which matches with Liu et al. [12] and Chen et al. [11] which were 100%. Pleural effusion was present   in one case of MAS (20%) which was higher than that of Liu et al. [12] study (13.7%) and those found in Chen et al. [11] which was (17.4%). Absence of lung sliding was present in 1case (20%) which was higher than Liu et al. [12] which was 16.2%. We found that the most specific finding in MAS is lung consolidation 5 (100%) (P value <0.05) statistically significant with 100% sensitivity and 40% specificity in comparison to 100% sensitivity and specificity and (p value <0.001) in prospective observational Liu et al study. [12].

However, there are some limitations in this study as follows: The number of respiratory distressed infants should be increase in future studies as well as complicated respiratory distress with air leak syndrome such as (pneumothorax , interstitial emphysema) cannot easily be discovered by using ultrasound machine.

Based on this study, we recommended informing pediatricians to know the importance of learning ultrasound and the importance of follow up neonates with respiratory distress for detection of change of ultrasound finding in each disease during convalescent stage.

Conclusions

Lung ultrasound is a non-invasive, bedside and repeatable method that could improve the management of neonatal respiratory distress. After 6 hours of Nasal Continuous Positive Airway Pressure (NCPAP), neonatal lung ultrasound is a useful predictor of the need for intubation over chest x-ray. Combined lung consolidation, pleural line abnormalities and absence of A line findings were  the most specific lung ultrasound findings in RDS which were present in 94.7% of cases (p value <0.001)  statistically significant  with 96% sensitivity and 63.3% specificity. Double lung point was found in 75% of cases which was statistically significant (p value <0.001) with 52% sensitivity and 100% specificity. Combined lung consolidation, pleural line abnormalities and interstitial lung were found in 87.5% of cases of pneumonia which was statistically significant (p value < 0.001) with 84.6% sensitivity and 77% specificity. It is worth noting  for  ultrasonographic  findings  in MAS we found  the most specific finding was  lung consolidation that was found in 100% of cases statistically significant (p value <0.001) with  100% sensitivity and 40% specificity.