To the Editor:
We have read with great interest the article by Ueda et al. 1regarding the intraoperative use of thoracic ultrasound for detection of pneumothorax and the accompanying editorial. In the past decade, lung ultrasonography has emerged as a sensitive and specific technique for detecting pneumothorax with the added benefit of avoiding the transport of the unstable patient and less radiation exposure as compared with computed tomography of the chest. We congratulate the authors for their fine contribution.
However, it was obvious from the two described scenarios that pneumothorax was the most likely diagnosis. Although thoracic ultrasonography has a very high sensitivity and specificity for detecting pneumothorax, the results are still operator dependent. In these two cases, if the diagnosis of pneumothorax could not be confirmed by ultrasonography, would this have changed the management? In these two situations, an expedited approach may be required because of the acute respiratory distress and hemodynamic decompensation due to positive pressure ventilation, in the presence of a pneumothorax. Ideally, after all other causes for the desaturation had been ruled out and if the suspicion for pneumothorax is high, a diagnostic pleural tap should be performed looking for rush of air and, if present, will necessitate the insertion of an intercostal tube. Awaiting ultrasonography results in unstable patients might cause additional delays in management that can be deleterious, risking tension pneumothorax.
The authors mentioned that the chest radiograph is still the gold standard to confirm pneumothorax when lung sliding is not present. This statement is inaccurate. Anteroposterior chest radiography is no longer considered the gold standard for diagnosing pneumothorax in the supine patient (case 1) or the multiple trauma patient (case 2).2The classic sign for the diagnosis of pneumothorax on chest radiograph is the visceral pleural stripe, which is visible as a thin curvilinear opacity along the lung and is separated from the chest wall by air in the apical pleural space.3This sign is rarely detected in supine patients unless there is a sizable pneumothorax. Small and moderate-sized pneumothoraces can easily be missed in that position. In the supine position, air usually accumulates in the least dependent pleural spaces (which are the anteromedial and subpulmonic recesses). Furthermore, another factor influencing the site of the pneumothorax is the presence of postoperative lung collapse (due to various reasons), where air will usually have a posteromedial distribution and will not be evident on the anteroposterior chest radiograph.4Supine anteroposterior chest radiograph has a very poor sensitivity for the detection of pneumothorax and has been reported as low as 36% in some studies5; the gold standard is computed tomography of the chest, as we previously demonstrated in our review of occult pneumothorax.3
Rib fractures are a prominent predictor of pneumothorax after trauma, with an odds ratio of 2.65 (confidence interval 1.34–5.25, P = 0.005).6In the second case presented, the patient fell from the second story of a building and sustained multiple bilateral rib fractures. Because of the patient's high pretest probability of pneumothorax and the sudden desaturation after 5 min of mechanical ventilation, despite breathing 100% oxygen, a diagnostic pleural tap looking for air rush should be performed without any further delay for imaging.
In conclusion, we agree that chest ultrasonography can be used in stable patients when there is a suspicion of pneumothorax. However, in the severely hypoxic or hemodynamically compromised patient with a high index of suspicion of pneumothorax, a diagnostic aspiration looking for rush of air should be performed and a chest tube should be inserted. Anteroposterior chest radiographs are not sensitive to look for pneumothorax in supine or multiple trauma patients.