Relationship between neonatal respiratory distress syndrome pulmonary ultrasonography and respiratory distress score, oxygenation index, and chest radiography grading

Abstract

BACKGROUND

Accurate condition assessment is critical for improving the prognosis of neonatal respiratory distress syndrome (RDS), but current assessment methods for RDS pose a cumulative risk of harm to neonates. Thus, a less harmful method for assessing the health of neonates with RDS is needed.

AIM

To analyze the relationships between pulmonary ultrasonography and respiratory distress scores, oxygenation index, and chest X-ray grade of neonatal RDS to identify predictors of neonatal RDS severity.

METHODS

This retrospective study analyzed the medical information of 73 neonates with RDS admitted to the neonatal intensive care unit of Liupanshui Maternal and Child Care Service Center between April and December 2022. The pulmonary ultrasonography score, respiratory distress score, oxygenation index, and chest X-ray grade of each newborn before and after treatment were collected. Spearman correlation analysis was performed to determine the relationships among these values and neonatal RDS severity.

RESULTS

The pulmonary ultrasonography score, respiratory distress score, oxygenation index, and chest X-ray RDS grade of the neonates were significantly lower after treatment than before treatment (P < 0.05). Spearman correlation analysis showed that before and after treatment, the pulmonary ultrasonography score of neonates with RDS was positively correlated with the respiratory distress score, oxygenation index, and chest X-ray grade (ρ = 0.429–0.859, P < 0.05). Receiver operating characteristic curve analysis indicated that pulmonary ultrasonography screening effectively predicted the severity of neonatal RDS (area under the curve = 0.805–1.000, P < 0.05).

CONCLUSION

The pulmonary ultrasonography score was significantly associated with the neonatal RDS score, oxygenation index, and chest X-ray grade. The pulmonary ultrasonography score was an effective predictor of neonatal RDS severity.

Key Words: Neonatal respiratory distress syndrome; Pulmonary ultrasonography; Ultrasonography score; Respiratory distress score; Oxygenation index; Chest X-ray grading

Core Tip: Current diagnostic and therapeutic evaluation methods for neonatal respiratory distress syndrome (RDS) often cause physical harm to neonates. No studies have yet reported the predictive value of pulmonary ultrasonography scores for neonatal RDS. This study evaluated the relationship between changes in the pulmonary ultrasonography score and the respiratory distress score, oxygenation index, and chest X-ray stage before and after treatment of neonatal RDS. Receiver operating characteristic curves showed that the pulmonary ultrasonography score predicted neonatal RDS severity.

INTRODUCTION

Neonatal respiratory distress syndrome (RDS) is a common clinical disease caused by the progressive collapse of alveoli owing to a lack of pulmonary surfactant (PS). RDS is most often seen in preterm infants with a gestational age of < 35 wk. The typical manifestations of RDS include progressive dyspnea, moaning, cyanosis, and an inspiratory triple concave sign within 4–12 h after birth. In severe cases, RDS can progress to respiratory failure in newborns, which can be life-threatening and is one of the main causes of neonatal death[1,2]. Therefore, conducting a proper evaluation of the severity of RDS can provide a reference for developing treatment plans for newborns with RDS and improve their prognosis. Currently, chest X-ray examination is the primary method for diagnosing and evaluating the efficacy of RDS in clinical practice. For many years, researchers in China and abroad have been exploring new methods to diagnose RDS in newborns because of the cumulative damage caused by repeated exposure to ionizing radiation. Pulmonary ultrasonography has been applied to the diagnosis of RDS[3]. Pulmonary ultrasonography has high sensitivity and specificity for the diagnosis of pulmonary diseases. It is both simple and noninvasive, can be performed at the bedside, and does not emit ionizing radiation, making it increasingly popular in clinical practice[4-6]. However, the usefulness of lung ultrasonography for the diagnosis and assessment of RDS has not been validated by research. This study aimed to analyze the relationships between pulmonary ultrasonography findings and scores, neonatal RDS scores, oxygenation indices, and lung X-ray grades to explore the practical value of pulmonary ultrasonography for diagnosing and assessing RDS severity. The results will be used to improve the accuracy of diagnosing RDS, the subsequent therapeutic efficacy, and the prognosis of affected children.

MATERIALS AND METHODS

Objective

This was a retrospective study that used quantitative variables and equation 1 was used to calculate the sample size[7]. In the equation, if the test level was α = 0.05, then the statistical quantity was U1 − α = 1.96. Based on pre-experimental results, the RDS neonatal ultrasonography score was S = 4 and the survey error was d = 1. After calculation, the required sample size was n ≥ 62. Considering possible cases with missing data, the sample size was increased by 10%. Finally, the study sample size needed to be ≤ 69 cases.

n = U²_1-α× S² ÷ d² (1)

According to the sample size estimation results, 73 newborns with RDS admitted to the neonatal intensive care unit of Liupanshui Maternal and Child Care Service Center between April and December 2022 were selected from our medical record information system and included in the study. After communicating with their families, authorization and signed informed consent forms were obtained. Of the 73 neonates with RDS, were 50 male and 23 were female. The gestational age was 26.43–41.29 wk, with an average of 32.97 ± 3.09 wk and the body weight was 950–3700 g, with an average of 1985.75 ± 674.03 g. The first ultrasonography was performed between 0.5 h and 12 h, with an average of 1.90 ± 2.01 h. The study was approved by the Medical Ethics Committee and was performed following the ethical principles for medical research involving human subjects of the World Medical Assembly Declaration of Helsinki[8].

Inclusion criteria: Eligible participants (1) Met the diagnostic criteria for RDS of the “European consensus guidelines on the management of neonatal respiratory distress syndrome in preterm infants”[9]; (2) Symptoms such as progressive dyspnea, inspiratory triple concave sign, and nasal fan appeared within 24 h after birth; and (3) Blood gas analysis showed hypercapnia and hypoxemia.

Exclusion criteria: (1) Pregnancy < 26 wk or > 42 wk; (2) Respiratory distress caused by asphyxia, infection, lung dampness, or other factors during childbirth; (3) Severe congenital heart defect or abnormal lung development; (4) Presence of genetic metabolic disease; (5) Presence of chromosomal abnormalities; (6) Twins or above; (7) Serious adverse reactions during treatment; (8) Pulmonary ultrasonography examination not performed before or within 12 h after treatment; and (9) Missing clinical data were reasons for exclusion.

Dropout criteria: Newborns in whom (1) The condition worsened or the patient was voluntarily withdrawn for other reasons; (2) Serious adverse reactions occurred during treatment; (3) Who did not undergo pulmonary ultrasonography examination before or within 12 h after treatment; and (4) Clinical data were incomplete were. withdrawn.

Treatment methods

The neonates were given noninvasive continuous positive airway pressure ventilation. The initial positive expiratory end positive pressure was 6–7 cmH₂O. The inhaled oxygen concentration was adjusted to maintain the target oxygen saturation of 90%–95%. When the newborn’s demand for inhaled oxygen concentration exceeded 40% or the chest X-ray was classified as grade III or IV, PS treatment was performed according to the relevant standards in the United Kingdom National Consensus expert consensus on surfactant replacement therapy for respiratory distress syndrome in preterm infants[10].

Inspection methods and relevant standards

Pulmonary ultrasonography examination and score: (1) The inspection instrument was a SonoSound M-Turbo portable color ultrasonography diagnostic instrument (SonoSound Company, United States) with a linear array probe (frequency 9–13 MHz); (2) The examination method was a. bedside pulmonary ultrasonography examination, requires the newborn to be in a quiet state in supine and lateral positions. The procedure followed the protocol for ultrasonography examination of bilateral lung areas in the “new international guidelines and consensus on the use of lung ultrasonography”[11]. Twelve lung areas in the upper and lower parts of the anterior, posterior, and lateral chest walls of the newborn were evaluated; (3) The pulmonary ultrasonography examination was performed before receiving PS treatment and within 12 h of respiratory support treatment. In addition, a dynamic re-examination of the newborn was conducted according to the condition. The video image data was saved and ultrasonography scoring was performed; and (4) The 12-zone ultrasonography scoring standards were previously described by Bouhemad et al[12] and included b the nature of the B-line and the presence or absence of lung consolidation. A new six-zone ultrasonography scoring system (Table 1) is proposed based on the actual operational structure. The B-line and pulmonary consolidation were assigned scores based on their respective characteristics. The total B-line score was 12 points, the total lung consolidation score was 24 points, and the total overall score was 36 points. Higher scores indicate a more severe neonatal condition.

Table 1 Ultrasonography B-line and dual-lung 6-zone pulmonary consolidation score in children with respiratory distress syndrome.

Classification	Ultrasonography changes	Ultrasonography scores
B-line	There are A-lines and the number of B-lines is < 3	0
	B-lines appear between two consecutive ribs or more, i.e. B-lines ≥ 3	1
	Dense and integrated B-line (without A-line)	2
Pulmonary consolidation	No pulmonary consolidation	0
	Involved intercostal space, lung consolidation range ≤ 1/2 of the lung field	3
	The range of the lung consolidation involving the intercostal space is greater than half of the lung field	4

Neonatal respiratory distress score: The respiratory scoring scale of the Canadian Critical Care Neonatal Care tutorial was used to evaluate the neonatal RDS. The scale consists of six items: respiratory frequency, oxygen demand, oxygen-intake depression, moaning, respiratory sounds, and gestational age. Each item is scored as 0–2 points for a total score of 0–12 points. The higher the score, the worse the respiratory condition of the newborn. Severity was based on the original description by Bouhemad et al[12]. Neonatal respiratory distress was divided into three levels by the score as mild (score of < 5 points), moderate (score = 5–8 points), and severe (score of > 8 points) respiratory distress.

Oxygenation index: Based on the relevant pulmonary ventilation parameters displayed on the ventilator, the oxygenation index was calculated by equations (2) and (3).

MAP = K [(PIP×Ti + PEEP × TE) ÷ Ti + TE] (2)

Oxygenation index= MAP × FiO₂ ÷ PaO₂ (3)

where MAP is the average airway pressure, K is the pressure waveform coefficient, Ti is the inspiratory time, PEEP is the positive end expiratory pressure, TE is the expiratory time, FiO₂ is the inhalation oxygen concentration, and PaO₂ is the arterial oxygen partial pressure.

The higher the oxygenation index, the worse the respiratory status of the newborn. Neonatal respiratory distress was divided into three levels by the oxygenation index: mild (oxygenation index = 4.0–7.9), moderate (oxygenation index = 8.0–15.9), and severe (oxygenation index > 16).

Lung X-ray grading: A Philips MultiDiagnosis X-ray machine was used to perform X-ray examinations on newborns, and their lungs were classified by the imaging findings. The grading standards are shown in Table 2, and the corresponding X-ray imaging manifestations for different X-ray grades are shown in Figure 1. Grades I and II indicate mild RDS, and grades III and IV indicate severe RDS.

Figure 1 X-ray imaging manifestations corresponding to different X-ray grades. A-D: X-ray grades 1, 2, 3, and 4, respectively.

Table 2 X-ray grading and imaging manifestations.

X-ray grading	X-ray imaging manifestations
0	No image changes
I	The transparency of both lung fields is generally reduced, with evenly scattered small particles and reticular shadows visible
II	Except for the aggravation of grade I changes, bronchial inflation sign can be seen, extending to the middle and outer zones of the lung field
III	The lesion worsens, the transparency of the lung field decreases further, and the cardiac and diaphragmatic margins appear blurry
IV	The entire lung field appears as a white lung, with more pronounced bronchial inflation signs resembling bald branches

Data collection

The pulmonary ultrasonography score, respiratory distress score, oxygenation index, and pulmonary X-ray grades of all children with RDS were collected before and within 12 h after treatment. Data were collected by two nurses who had received unified professional training. An ultrasonography functional physician and a neonatal physician jointly interpreted the pulmonary ultrasonography for diagnosis and grading.

Statistical methods

SPSS 26.0 (IBM Statistics for Windows, IBM Corp., Armonk, NY, United States) was used for data processing and analysis. The Kolmogorov–Smirnov test was performed to verify that the measurement data, reported as means ± SD, were normally distributed. Two categories of baseline data were compared by independent t-tests, and three categories of baseline data were compared by single-factor analysis of variance. Values of clinical indicators before and after treatment were compared with the paired t-test. The Wilcoxon rank sum test was used to compare rank data groups of binary baseline data for the number and percentage (n, %) of use cases of counting data, and the Kruskal–Wallis test was used to compare rank data groups of ternary baseline data. Spearman correlation analysis was performed to assess the relationships of the RDS neonatal pulmonary ultrasonography score, respiratory distress score, oxygenation index, and chest X-ray grade. Graph Prism 9 (GraphPad Software, Boston, MA, United States) was used for plotting. Values of P < 0.05 indicated statistically significant differences.

RESULTS

Comparison of the neonatal RDS ultrasonography scores, respiratory distress scores, oxygenation indexes, and chest X-ray grades before treatment

A total of 73 valid datasets were collected, with a data recovery effectiveness rate of 87.95%. There were no statistically significant differences in the ultrasonography scores, respiratory distress scores, oxygenation index, and chest X-ray grades of RDS newborns among different sexes, gestational weeks, weight, and first ultrasonography time (P > 0.05) before treatment (Table 3). The pulmonary ultrasonography imaging results of one newborn from each of the different chest X-ray grade groups were also analyzed. The details of the pulmonary ultrasonography scores are shown in Figures 2-5.

Figure 2 X-ray grade 1 respiratory distress syndrome neonatal pulmonary ultrasonography images. A, B, E: Representative images showing increase in B-lines in the anterior chest of R1–R2/L1–L2. Real-time ultrasonography shows that B-lines and A-lines alternate with lung slip, resulting in 1 point each; C, D, F, G: Representative images showing ground-glass-like changes in each region of R3–R4/L3–L4 R5–R6/L5–L6, with 2 points each and a total ultrasonography score of 10 points.

Figure 3 X-ray grade 2 respiratory distress syndrome neonatal pulmonary ultrasonography images. A, B, F–H: Representative images showing ground-glass-like changes in the R1–R4/L1–L4 region. Transverse scanning confirms continuous interruption of pleural lines with snowflake-like changes, similar to lung adenocarcinoma in situ, but in reality, they indicate early or mild lung consolidation changes, with 2 points for each region; C–E, I, J: Representative images showing the disappearance of pleural and A-lines in the R5–6/L5–6 region, with pulmonary consolidation accompanied by bronchial inflation sign. Transverse scan confirms that each area scores 6 points, and the total ultrasonography score is 20 points.

Figure 4 X-ray grade 3 respiratory distress syndrome neonatal lung ultrasonography images. A: Ground-glass-like changes in the right lung R1–R2, as shown by the A-line, resulting in 2 points; B, E–G: Representative images showing consolidation of the left lung L1–L4 and right lung L3–L4 in half of the lung field, with 5 points for each area; C, D, H–J: Representative images showing consolidation of R5–R6/L5–L6 involving the entire lung field, with 6 points for each area and a total ultrasonography score of 29 points.

Figure 5 X-ray grade 4 respiratory distress syndrome neonatal pulmonary ultrasonography images. A–H: Representative images showing involvement of consolidation with bronchial inflation sign in each longitudinal area. The transverse scan confirms the existence of the above changes, with 6 points for each area and a total ultrasonography score of 36 points.

Table 3 Comparison of respiratory distress syndrome neonatal ultrasonography score, respiratory distress score, oxygenation index, and chest X-ray grade before treatment.

Items		n	Ultrasonography score, points	Respiratory distress score, points	Oxygenation index	Chest X-ray grade
						0	I	II	III	IV
Sex	Male	50	26.68 ± 7.41	7.60 ± 1.32	7.99 ± 2.64	0	1	13	17	19
	Female	23	26.87 ± 7.35	7.83 ± 0.98	7.76 ± 1.59	0	1	7	5	10
t/Z			−0.102	−0.730	0.388	−0.057
P value			0.919	0.468	0.699	0.955
Pregnancy duration in wk	< 32	29	25.66 ± 7.83	7.69 ± 1.26	7.59 ± 2.76	0	2	7	10	10
	32–36	35	26.77 ± 6.95	7.57 ± 1.29	8.01 ± 2.17	0	0	11	11	13
	> 36	9	30.11 ± 6.86	8.00 ± 0.87	8.66 ± 1.40	0	0	2	1	6
F/H			1.277	0.436	0.744	2.073
P value			0.285	0.648	0.479	0.355
Weight in g	< 1500	21	26.29 ± 8.28	7.76 ± 1.22	7.87 ± 3.06	0	1	6	5	9
	1500–2500	38	26.29 ± 6.85	7.53 ± 1.22	7.56 ± 2.03	0	1	10	14	13
	> 2500	14	28.64 ± 7.39	7.93 ± 1.27	8.97 ± 1.70	0	0	4	3	7
F/H			0.576	0.625	1.901	0.494
P value			0.565	0.538	0.157	0.781
First ultrasonography time in h	< 1	15	29.20 ± 6.13	8.07 ± 0.80	9.02 ± 2.65	0	0	2	3	10
	1–1.5	39	25.23 ± 7.68	7.59 ± 1.33	7.68 ± 2.30	0	2	12	13	12
	> 1.5	19	27.89 ± 7.09	7.53 ± 1.26	7.55 ± 2.06	0	0	6	6	7
F/H			1.954	1.000	2.135	5.689
P value			0.149	0.373	0.126	0.058

Data are mean ± standard deviation or n (%).

Comparison of the neonatal RDS ultrasonography scores, respiratory distress scores, oxygenation indexes, and chest X-ray grades before and after treatment

The RDS neonatal ultrasonography scores, respiratory distress scores, oxygenation indexes, and chest X-ray grades were significantly lower after treatment than before treatment (P < 0.05) (Table 4).

Table 4 Comparison of the respiratory distress syndrome neonatal ultrasonography score, respiratory distress score, oxygenation index, and chest X-ray grade before and after treatment.

Items		Before treatment, n = 73	After treatment, n = 73	t/Z	P value
Ultrasonography score (points)		26.74 ± 7.34	15.12 ± 6.11	17.324	< 0.001
Respiratory distress score (points)		7.67 ± 1.23	3.93 ± 1.25	47.887	< 0.001
Oxygenation index		7.92 ± 2.35	5.84 ± 2.13	9.543	< 0.001
Chest X-ray grade	0	0 (0.00)	32 (43.84)	−7.460	< 0.001
	I	2 (2.74)	24 (32.88)
	II	20 (27.40)	16 (21.92)
	III	22 (30.14)	1 (1.37)
	IV	29 (39.73)	0 (0.00)

Data are mean ± standard deviation or n (%).

Relationship between neonatal RDS ultrasonography scores, respiratory distress scores, oxygenation indexes, and chest X-ray grades before and after treatment

The RDS neonatal ultrasonography scores, respiratory distress scores, oxygenation indexes, and chest X-ray grades showed a significant decrease after treatment compared to before treatment (P < 0.05) (Table 4). Of these, the linear relationship shown in Figure 6A–D was relatively good, but the scatter in Figure 6E–F was relatively broad, with a relatively poor linear relationship. Spearman’s correlation analysis showed that the ultrasonography scores of the RDS newborns before and after treatment were positively correlated with the respiratory distress scores, oxygenation indexes, and chest X-ray grades (< 0.05) (Table 5).

Figure 6 Scatter plot of the relationship between the respiratory distress syndrome neonatal ultrasonography score, respiratory distress score, oxygenation index, and chest X-ray grade before and after treatment. A: Relationship between the pretreatment ultrasonography scores and respiratory distress scores; B: Relationship between the pretreatment ultrasonography score and oxygenation index; C: Relationship between the pretreatment ultrasonography scores and chest X-ray grade; D: Relationship between the ultrasonography scores and respiratory distress scores after treatment; E: Relationship between the ultrasonography scores and oxygenation index after treatment; F: Relationship between the post-treatment ultrasonography score and chest X-ray grade; the red circle in the figure represents the corresponding data of each sample indicator.

Table 5 Correlation between the respiratory distress syndrome neonatal ultrasonography score and respiratory distress score, oxygenation index, and chest X-ray grade before and after treatment (n = 73).

Comparator	Ultrasonography score
	Before treatment		After treatment
	ρ	P value	ρ	P value
Respiratory distress score	0.446	< 0.001	0.429	< 0.001
Oxygenation index	0.703	< 0.001	0.748	< 0.001
Chest X-ray grade	0.859	< 0.001	0.764	< 0.001

Predictive efficacy of the pulmonary ultrasonography scores for chest X-ray grades of newborns with RDS

To verify the value of the pulmonary ultrasonography score for predicting neonatal RDS severity, the pulmonary ultrasonography score was used as a variable and the chest X-ray grade as a categorical variable to perform receiver operating characteristic (ROC) analysis. The results showed that the pulmonary ultrasonography score effectively predicted the severity of the RDS condition of newborns. Table 6 shows the ROC-related parameters, and Figure 7 shows the ROC curves.

Figure 7 Receiver operating characteristic correlation of the pulmonary ultrasonography score with newborn respiratory distress syndrome severity. The green line is the receiver operating characteristic (ROC) of pulmonary X-ray grades I and II; the blue line is the ROC of pulmonary X-ray grades II and III; and the purple line is the ROC of pulmonary X-ray grades III and IV.

Table 6 Respiratory distress syndrome parameters.

Categorical variable	AUC	SE	P value	Youden index	Optimal cutoff value	Sensitivity, %	Specificity, %
I–II	1.000	0.000	< 0.001	1.000	> 12	100.00	100.00
II–III	0.805	0.077	< 0.001	0.682	> 24	68.18	100.00
III–IV	0.946	0.030	< 0.001	0.795	> 30	93.10	86.36

AUC: Area under the curve; SE: Standard error.

DISCUSSION

The theory of pulmonary ultrasonography was first proposed by Lichtenstein in 1992. The total reflection of ultrasonography when encountering gas in the alveoli and the influence of a bony chest led most researchers to believe that pulmonary ultrasonography had limitations that prevented it from becoming a routine auxiliary examination method in the early stages of development. After years of research and clinical practice, it has been found that under pathological conditions, the gas–liquid ratio of pulmonary tissue changes, greatly reducing the effect of gas in the alveoli on imaging. The sensitivity and specificity of pulmonary ultrasonography diagnosis have increased with advancements in ultrasonography technology. Given that this technique is convenient, radiation free, and repeatable, pulmonary ultrasonography technology is widely used in the clinical diagnosis and treatment of various pulmonary diseases. In newborns with RDS, pulmonary ultrasonography can often recognize and distinguish between normal and abnormal pulmonary tissue based on features such as extensive alveolar collapse, pulmonary interstitial edema, and the formation of an eosinophilic transparent membrane. This differentiation is possible because of the formation of ultrasonography reverberation artifacts[13,14]. In this study, the ultrasonographic examination of the lungs of. newborns with RDS was characterized by abnormal pleural lines, abnormal A-lines, the presence of B-lines, manifestations similar to pulmonary adenocarcinoma in situ, and pulmonary consolidation changes accompanied by the bronchial inflation sign, which were consistent with the pulmonary ultrasonography results of RDS newborns in previous studies[15,16].

The neonatal respiratory distress score was derived from the Canadian ACoRN tutorial, which has the characteristics of simplicity, accuracy, and high clinical applicability[17]. The neonatal respiratory distress score objectively and accurately assesses the respiratory status of newborns, and the protocol resulted in dividing RDS newborns into three score levels. Noninvasive continuous positive airway pressure ventilation was provided for newborns with moderate respiratory distress, and invasive ventilator-assisted ventilation was provided for newborns with severe respiratory distress, which is similar to the methods used in clinical practice. This score also provided a good diagnosis and treatment reference for physicians with relatively limited clinical experience. The oxygenation index reflects the ventilation function of the lungs. Some studies have reported that dynamic changes in the oxygenation index can effectively predict the prognosis of patients with RDS[18]. This is because the extravascular lung water index is closely related to damage of the pulmonary vascular endothelium and alveolar epithelial cells. An increase of the extravascular lung water index often indicates aggravated lung injury. However, when the extravascular lung water is more than twice the normal value, gas diffusion and lung function are affected, leading to pulmonary edema, thereby reducing the static compliance of the oxygenation index[19]. In addition, Picano and Pellikka[20] noted that the number of B-lines was related to the extravascular lung water content and reflected neonatal RDS severity. That is consistent with the results of this study regarding the effect of lung ultrasonography. However, Tang et al[21] reported that the oxygenation index was not a prognostic factor for neonatal RDS. Chest X-ray is currently the most commonly used imaging technique for diagnosing RDS and assessing RDS severity. However, chest X-ray image quality is affected by factors including neonatal respiratory movement and body position. Importantly, the ionizing radiation of X-rays can affect the physical health of newborns. The findings of this study indicated that the ultrasonography score of newborns with RDS was positively correlated with the respiratory distress score, oxygenation index, and chest X-ray grade (P < 0.05), indicating that the pulmonary ultrasonographic findings and score are also closely related to RDS severity. The pulmonary ultrasonography findings and score can be used for the diagnosis and evaluation of RDS. The ROC analysis results showed that the pulmonary ultrasonography score predicted and identified neonatal RDS severity as grades I–II, II–III, and III–IV, with a sensitivity of 68.18%–100.00% and specificity of 86.36%–100.00%, which support use of the score as a predictor of neonatal RDS severity. Previous studies that compared the diagnostic efficacy of pulmonary ultrasonography and chest X-rays in RDS found that the diagnostic results of the two examination methods were highly consistent (kappa = 0.647)[22]. This finding is consistent with our study results. In this study, we used a new six-zone pulmonary ultrasonography scoring method in line with that of Brat et al[23] who proposed a pulmonary 6-zone ultrasonography scoring method that used the same scores for different ranges of pulmonary consolidation and coexistence with different B-line degrees, which may affect the final disease evaluation results. However, the new pulmonary 6-zone ultrasonography scoring method used in this study had independent scores for the B-line and pulmonary consolidation and did not affect the overall scoring results[24].

CONCLUSION

In summary, pulmonary ultrasonography findings and scores had varying degrees of correlation with the neonatal RDS score, oxygenation index, and chest X-ray grade, and were used clinically as predictors of the neonatal RDS condition. However, owing to the small sample size used in this study, the results may be biased. Future studies with larger sample sizes would be useful to further explore the value of pulmonary ultrasonography findings and scores for evaluating neonatal RDS conditions.