Lung point and power slide signs help to improve the accuracy of lung ultrasound to diagnose pneumothorax.

Sir,

We read, with great interest, original article by Abdalla et al. published in Saudi Journal of Anesthesia, 2016.[1] We congratulate the authors for their nice work.

Authors mentioned that when lung sliding and comet tail artifacts (on B-mode) and seashore sign (on motion mode) were not seen on lung ultrasound (US), pneumothorax (PTX) was provisionally diagnosed. However, there are reasons, other than PTX, for the abolishment of lung sliding in mechanically ventilated patients. These include endobronchial intubation, large consolidations, acute respiratory distress syndrome, pulmonary fibrosis, pleural adhesions, and phrenic nerve palsy. Hence, though the negative predictive value of lung sliding to rule out PTX is 99.2–100%, its absence does not necessarily indicate that PTX is present.[2] On the other hand, the presence of B-lines or comet tail artifacts rules out PTX with certainty. Another sign which is 100% specific for the diagnosis of PTX is a demonstration of “lung point.”[3] “Lung point” sign occurs at the border of a PTX. It is a transition between the normal sliding lung and no sliding seen due to collapsed lung. It is helpful in determining the actual size of the PTX. Lung point can be obtained by moving the probe away from the area where lung sliding was found to be absent. However, lung point is not visible in case of massive PTX causing complete lung collapse, which warrants immediate chest drain insertion. Hence, we suggest that looking for lung point, in addition to the demonstration of absence of lung sliding and B-lines, would not only improve the specificity of diagnosis of PTX but also would help in making a therapeutic decision.

Authors also mentioned about few false positive cases where there was a provisional diagnosis of PTX on US, but they turned out to be lung overinflation and subcutaneous emphysema on computed tomography. In severe cases of lung overinflation, there is a minimal expansion of lung on inspiration leading to minimal lung sliding seen on US. It can be mistaken as a lack of lung sliding. Moreover, in subcutaneous emphysema, pockets of air in subcutaneous tissues make identification of pleural line difficult, leading to poor recognition of lung sliding. We suggest the use of power Doppler to identify lung sliding (power slide sign). Power Doppler is very sensitive and picks up subtle flow and movement. If there is lung sliding present, power Doppler will light up the sliding pleural line with color flow. This technique is helpful in cases of subtle sliding when direct visualization is difficult. However, any movement of patient's body or probe during the examination may produce an artifact leading to an error in the judgment.[4]

Finally, we agree with the authors that chest ultrasonography is a quick, bedside, noninvasive, and accurate modality in the diagnosis of PTX in critically ill mechanically ventilated patients.

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