Anesthesiology:
doi: 10.1097/ALN.0b013e318249de30
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Ueda, Ken-ichi M.D.; Ross, Alan F. M.D.; Ahmed, Waseemuddin M.D.*

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Thank you for your interest in our case report.1 The following are replies to Dr. Omar et al. and to Dr. Verniquet.
Dr. Omar et al. offer several important considerations regarding occult pneumothorax in trauma patients. However, our operating room patient population differs because most of these cases are elective operations. In case 1 (elective Nissen fundoplication), the etiology of pneumothorax was surgical entry into the pleural space causing lung collapse, not tension pneumothorax. A diagnostic pleural tap may not have yielded a rush of air and may have failed as a test for pneumothorax. Other circumstances (such as mucous plug) can cause low oximeter saturation, high airway pressures, and decreased breath sounds that resemble pneumothorax. Here, an unnecessary pleural tap could potentially make circumstances worse. If the lung-sliding sign was appreciated, the diagnostic tap would have been avoided and other differential diagnoses could be advanced. A key advantage of ultrasound is its ability to noninvasively contribute to the diagnosis.
Dr. Verniquet correctly stated the mechanism by which air in the pleural space disrupts the lung sliding sign. Thank you for that clarification. Dr. Verniquet also made several observations about the diagram that accompanied the ultrasound image. First, it was noted that the pleural line was visible beneath the rib structure. It was suggested that cartilage rather than rib was actually imaged because heavy rib calcification will cast an ultrasonic shadow and make the pleural line not visible. Although this is a possibility, the pleural line is often visible at the edges of known rib images. The second critique concerned the region of the diagram labeled lung parenchyma. Dr. Verniquet indicated that normal air-filled lung is not visible by ultrasound. However, the purpose of the diagram and image was to help interpret the lung sliding sign shown in the video. The major point is that the lung sliding sign implies that lung parenchyma, not pneumothorax, is present in this area. Similarly, the presence of a comet-tail artifact implies the presence of air-filled lung rather than pneumothorax.2
We also acknowledge the comments by Dr. Verniquet and Dr. Omar et al. that computed tomography rather than chest x-ray is the gold standard for diagnosis of pneumothorax. However, some have described a gold standard to be the best available test rather than the perfect test.3 From an operating room perspective, timely access to computed tomography of the chest is distinctly limited compared with that of emergency departments and intensive care units. Further, the intraoperative question is to identify a large, compromising pneumothorax. The utility of thoracic computed tomography to identify a small, occult pneumothorax carries less clinical relevance for the operating room patient.4,5 Therefore, it is arguable that a portable chest x-ray, albeit its lower sensitivity to detect a smaller pneumothorax compared with computed tomography, is the gold standard to image an operating room pneumothorax. Increasing the availability and experience with ultrasound in anesthesia will allow us to rule out potential pneumothorax in clinical practice in a fast and noninvasive manner.
Ken-ichi Ueda, M.D., Alan F. Ross, M.D., Waseemuddin Ahmed, M.D.,* *University of Iowa, Iowa City, Iowa. waseemuddin-ahmed@uiowa.edu
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References

1. Ueda K, Ahmed W, Ross AF: Intraoperative pneumothorax identified with transthoracic ultrasound. ANESTHESIOLOGY 2011; 115:653–5

2. Lichtenstein D, Mezire G, Biderman P, Gepner A: The comet-tail artifact: An ultrasound sign ruling out pneumothorax. Intensive Care Med 1999; 25:383–8

3. Versi E: “Gold standard” is an appropriate term. BMJ 1992; 305:187

4. Ball CG, Kirkpatrick AW, Laupland KB, Fox DL, Litvinchuk S, Dyer DM, Anderson IB, Hameed SM, Kortbeek JB, Mulloy R: Factors related to the failure of radiographic recognition of occult posttraumatic pneumothoraces. Am J Surg 2005; 189:541–6, discussion 546

5. Ball CG, Kirkpatrick AW, Laupland KB, Fox DI, Nicolaou S, Anderson IB, Hameed SM, Kortbeek JB, Mulloy RR, Litvinchuk S, Boulanger BR: Incidence, risk factors, and outcomes for occult pneumothoraces in victims of major trauma. J Trauma 2005; 59:917–24, discussion 924–5

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