These cases highlight the importance of evaluating NP using LU in the critically ill neonate in order to plan management, particularly with surgical patients or those with several drainage interventions.
We have reported 4 neonates with complex diagnoses. All had in common prior manipulation of the chest (cardiac/esophageal surgery or previously inserted pleural drainage). LU optimized management in all of them: In patient 1, detailing the amount of pleural effusion and air, and permitting an ultrasound-guided technique. In patients 2 and 4, demonstrating that anterior thoracocentesis is not always the best solution. In patients 2 to 4, it permitted dynamic, close control of evolution in order to decide on the best therapeutic approach.
LU is an easy to use examination, which is quick, cheap, free of ionizing radiation, and can be performed by the same clinician attending the patient (6). Several studies have demonstrated a steep learning curve; shorter than for other uses of point-of-care ultrasound (7).
Classically, chest x-ray has been the gold standard for diagnosis in the sick newborn with respiratory diseases. However, LU has demonstrated a higher sensitivity and specificity in several diseases, and the typical pattern of almost all neonatal lung diseases have already been described (5, 8).
Typical findings of pneumothorax in LU are: A-lines pattern, absence of lung sliding and B-lines, together with lung point identification. The latter has a 100% specificity, and it should be systematically identified in order to confirm the diagnosis (4). Stratosphere sign on M-mode, as a surrogate sign of the absence of pleural sliding, can be identified (9, 10). Experience is needed in order to rule out some ultrasonographic findings which could be misinterpreted (11).
In the critically ill patient, in supine position, the air is usually located in the anterior part of the chest and, as the amount of air increases, the lung point moves towards the patient's back, until its disappearance in massive pneumothoraces(12). However, in our cases, no air was identified in the anterior area, and instead two lung points were seen, limiting the pneumothorax to the lateral/posterior area. We hypothesized that, in the event of worsening, each lung point would move towards anterior and posterior areas respectively, although this assumption has not been analyzed previously, to the best of our knowledge.
This kind of NP with atypical location in the lateral or posterior area of the chest can occur when interventions have previously been performed on the thorax (cardiac surgery, pleural drainage, etc.), leading to pleural adherences that limit the free movement of the air between the two layers. In x-rays, this fact can be difficult to assess, due to the “2-dimensional image” obtained, unless performing an x-ray with lateral views (exposing the child to extra radiation and often risky manipulation). However, this task is very easy to achieve using LU, defining the precise location of the lung point, reducing radiation, and increasing the safety of the procedures performed in newborns, such as emergent thoracocentesis and drainage insertion(6, 13–15).
In addition to studying its location, LU is useful for checking pneumothorax resolution following pleural drainage insertion, and to serially confirm evolution before removal (4): its use has also been related to shortened hospital stays in newborns (15). In our experience, it is a useful instrument for monitoring the patient and anticipating any clinical deterioration.
In conclusion, this study stresses the importance of LU in the management of a neonate with suspected pneumothorax, particularly in complex patients with previous thoracic manipulation, as previously described in some clinical-ultrasound protocols as SAFE (Sonographic Assessment of liFe-threatening Events) algorithm(6).
Long experience of researchers in the use of LU and retrospective analysis are potential limitations of this study; however, we consider that the results are relevant and objective, and create an interesting area for further research.
More studies are needed in order to confirm our findings and hypothesis, so a better understanding of pneumothorax physiopathology in this critical population can be described.