Background

Two third of the neonatal mortality is related to neonates who weigh lower than 2500 gr at the time of birth, and even though very low birth weight infants consist less than 1% of all births, 50% of neonatal mortality is related to this group (1,2).

The most common causes of pre-term neonatal mortality are bronchopulmonary dysplasia and respiratory distress syndrome (RDS). Bronchopulmonary dysplasia (BPD) is a chronic lung disease that is seen most often in severely premature babies (birth weight lower than 1,000 grams at birth) who developed RDS. Respiratory distress syndrome (RDS) is a life-threatening lung disorder in which a baby’s lungs are not fully formed and cannot function outside the uterine. This condition primarily affects premature babies (3-5).

Pneumothorax, congenital diagraphmatic hernia, pneumonia, sepsis, temporary tachypnea and respiratory distress syndrome (RDS) have been proposed as the main causes of respiratory distress. RDS is one of the most common causes of death in premature infants (6) which is caused by developmental insufficiency of surfactant production and structural immaturity in the lungs (7). Labored breathing which is characterized by grunting, nasal flaring and the use of accessory muscles of respiration is the most common clinical sign of RDS.  Low birth weight has been regarded as one of the leading causes of RDS as most of the neonate with birth weight of 500-1500 suffer from RDS (8).    

Chest X-rays have shown promising results regarding the early diagnosis of respiratory distress (7). Fisch in 2006 declared that chest x-rays in preterm neonates can provide useful information for diagnostic procedures (9). Diffuse reticulogranular, grand glass pattern and air-bronchogramare classic radiographic signs ofrespiratory distress (8). Also it has been declared that normal radiographic patterns 6 hours after labor exclude any chance of RDS ^(10-12). Although Chest X-rays showed promising results in detecting respiratory distress, they cannot efficiently differentiate initiating causes of respiratory distress like RDS and pneumonia.

Objectives: Since there are no conclusive studies regarding the specificity and sensitivity of radiographs in detecting respiratory distress causes, the present study was designed to determine the sensitivity, specificity and clinical value of chest radiography of neonates with respiratory distress.

Patients and methods

This was a descriptive-analytic study which was held in the Imam Reza and 22 Bahman hospitals in Mashhad University of Medical Science, Iran during 2011-2012. 102 neonates who were admitted in NICU with respiratory distress diagnosis were included in the present study. When respiratory distress was confirmed, useful information ) maternal age, history of mother disease, history of drug usibirth weight, height, gender, delivery mode, date of delivery, apgar score at birth, symptoms at time of referring, etc.(, were recorded in the questionnaire.

RDS was diagnosis by a neonatal specialist based on clinical symptoms and course and ABG and infection roll out and chest X-ray, then chest X-ray was given to a radiologist without awareness of the above diagnosis and then the results were statistically collected. Different interpretations included: collapses, pneumothorax, pleurisy, heart condition, mediastina, pulmonary vessels, diaphragm condition, lucencies in the lung and the presence of any cavity, mass and unusual opacity were diagnosed and recorded in the questionnaire. After specific clinical and para-clinical procedures the definite diagnosis was made and recorded in the questionnaire. Finally, final diagnosis has been confirmed by another neonatologist.

Statistical Analysis

We assessed the prevalence of these parameters and performed the statistical analysis by SPSS v.15. Chi-square test and Exact fisher test were used. The statistical significance was at P

Results

From 58 (56.9%) of neonates were male and 44 (43.1) were female and 66 (64.7%) were born with cesarean and 36 neonates (35.3%) with natural delivery and also 88 (76%) birth weight

Diagnosis of the disease was performed based on neonate's age, presence or absence of delivery events, clinical course, ABG, and also observation of CXR evidences, presence or absence of evidence of infection and blood cultures, echocardiography. Invasive proceeding such as chest tube insertion, needle aspiration and finally surgery were performed.

Table 1 demonstrates the frequency of radiographic observations in chest x-rays. It can be concluded that chest X ray haziness and bronchogram were the most common radiographic signs. Also presence of the pneumothorax was the least common sign in x-rays. After the signs of pneumothorax intensified, missed cases were revised and definitive diagnosis was assigned after consulting with the radiologist. 

Also table 1 show the final clinical diagnosis of patients who were admitted with clinical signs of respiratory distress. According to the table 3, it was seen that RDS had the highest rate of frequency following by Transient Tachypnea of the Newborn. Also hernia showed the least rate of frequency. In Table 1 represents the frequency rate of final radiographic diagnosis. It was observed that RDS, pneumonia and bronchopneumonia had the highest rate of frequency. Interestingly in 18% of cases, neonates were diagnosed to be radiographically healthy.

Based on table 1, it can be concluded that from 39 clinical diagnosis of RDS 25 of them were confirmed by radiographs (64.1%). All clinical diagnosis of hernia and pneumothorax were confirmed by radiographs. These results are presented in table 1.

According to table 2 it can be said that totally 79.4% of clinical diagnosis were confirmed by radiographs and in 20.6% of cases there was no coordination between clinical and radiological observations. Table 3 represents the falsepositive and negative radiological and clinical observations for different radiologic diagnosis.

Discussion

Chest X-ray is one of the main steps in respiratory distress diagnostic procedure, therefore it is necessary to investigate the value of radiography role in this disease. In the Marini study in 1997 the sensitivity and specificity of chest x-ray in neonates were 89.1% and 86.9% respectively in detecting respiratory distress (13). In the present study we precisely determined the sensitivity and specificity of chest x-rays in detecting different causes of respiratory distress.

In the present study the interpretation of chest x-rays was based on the criteria which were used by Marini C in 1997. It was concluded that chest x-ray haziness and bronchogram were the most common radiographic signs.

In the present study, boys consisted 56.9% of patients who were admitted to NICU. This finding is in agreement with Hashemi zadeh’s study which declared that 61% of patients suffering from respiratory distress were boys (14).

In Berg A’s study respiratory distress was said to be one of the major complications of cesarean (15). This finding was also confirmed in the present study as just 35.3% of neonates had natural delivery.    

Hyaline membrane disease or RDS Respiratory distress syndrome:

In the present study the specificity(the percentage of healthy people who are correctly identified as not having the condition) and sensitivity (the percentage of sick people who are correctly identified as having the condition) of the radiographic test was 82.5 and 35.8% respectively. While in the Kurl’s study clinical and radiographic diagnosis matched properly in 95% of cases (11).

Pneumothorax:

The specificity and sensitivity of the test in diagnosing Pneumothorax were 100%. In Marini C study there were 5 patients suffering from pneumothorax and all of them were diagnosed (13). Also Kurl indicated that the consistency of radiographic and clinical diagnosis is 78% (11).

Pneumonia:

The sensitivity and specificity of the radiographic tests were 73% and 87% respectively in the present study. In Mathur study in 2002, chest x-rays were normal in 15% of patients suffering from pneumonia (sensitivity 15%) (12).

Congenital heart disease:

16.6% and 98% sensitivity and specificity were reported for radiographic tests respectively in the present study. In Fonseca study in 2004 the chest x-rays represented low sensitivity for heart structural disease (26%-59%) (16). Also it was revealed that chest x-rays do not change the trend of treatment and diagnosis of patients with congenital heart diseases (17).

Congenital diagraphmatic hernia:

In the present study the sensitivity and specificity of radiographic tests were 100%. In Marini C study 3 cases of hernia were clinically diagnosed and all of these cases were confirmed by radiographs (13).

Transient tachypnea of neonates (TTN):

The sensitivity and specificity of radiographic tests were 0 and 100% respectively. In Kurl study just 48% of clinical and radiographic diagnosis matched properly (11). In the present study none of the neonates who were suffering from TTN were diagnosed by radiographs.  Also Ponhold revealed that the diagnosis of TTN is mainly based on clinical signs and symptoms (18).

Finally in the present study 79.4% of clinically diagnosed cases were confirmed by radiographs. Also in Kurl’s study, 66.6% of clinical and radiographic diagnosis matched properly (11).

Conclusion

Although chest radiography is used as one of the most usual and accessible diagnostic tools in respiratory distress syndrome but diagnostic value of RDS based on radiologist opinion were about one-third of all cases and has low sensitivity.

Acknowledgement

This study has been financially supported by Medical Faculty of Islamic Azad University in Mashhad.  The authors are thankful to Dr Ahmad shah Farhat, Dr Ashraf Mohammad zade (Pediatrics Department) and all coworkers from Neonatal research center in ImamRezaHospital in Mashhad University of Medical Science, Iran.

Conflict of Interest: None

 Financial Disclosure: Authors who have no relevant financial interests are asked to provide a statement indicating that they have no financial interests related to the material in the manuscript.