Case Presentation by Dr. Sean Michael, MD
Visual Stimulus Case:
A 59-year-old man with COPD presents with acute dyspnea. His breath sounds are nearly inaudible. He is tripoding with accessory muscle use and suprasternal retractions. Temperature is 37.7°C, heart rate 112, respiratory rate 36, blood pressure 168/92, and oxygen saturation 89% on 2 liters via nasal cannula. Glucocorticoids and nebulized bronchodilators are administered. Bedside thoracic ultrasound is performed and demonstrates the following M-mode image in the right second intercostal space:
- The most likely etiology of the ultrasonographic finding above is:
A. Emphysematous bulla or apical bleb
B. Iatrogenic pneumothorax
C. Lobar pneumonia
D. Primary spontaneous pneumothorax
Additional images are obtained of the right chest at the level of the fifth intercostal space:
- Given the new information obtained in this image, which of the following is the best course of action:
A. CT Thorax
B. Intravenous antibiotics
C. Non-invasive positive pressure ventilation
D. Tube thoracostomy
- The findings in the second ultrasound image serve mostly to:
A. Increase diagnostic sensitivity (ie. have a high negative predictive value)
B. Increase diagnostic specificity (ie. have a high positive predictive value)
C. Predict a decreased risk of mortality
D. Predict an increased risk of treatment failure
Answers and explanation:
(Note: This explanation assumes that you understand the basics of lung ultrasound. If you need a refresher, there are lots of great online resources.)
This patient presented with an apparent moderate to severe COPD exacerbation with hypoxia and poor air exchange on lung auscultation. Bedside lung ultrasound (image 1) demonstrates absence of pleural sliding on M-mode. In the setting of COPD (or many other critical illness states), the absence of lung sliding may be caused by any number of pathophysiologic conditions. While the absence of lung sliding is quite sensitive for pneumothorax of any etiology, in comparison to patients with traumatic pneumothorax, patients with non-traumatic dyspnea may have numerous other causes of poor lung sliding, which may increase the false-positive rate for ultrasound exams (Slater 2006, Lichtenstein 2008).
In this clinical presentation, the most likely reason for the absence of lung sliding is an emphysematous bulla/apical bleb (question 1, answer A). Bullae are common in COPD, especially in advanced disease, and a ruptured apical bleb is a common cause of secondary spontaneous pneumothorax (Noppen 2008). While iatrogenic pneumothorax (question 1, answer B) is a known complication of a number of procedures, this patient did not undergo any high-risk interventions, such as transthoracic needle aspiration, central venous access, thoracentesis, transbronchial or pleural biopsy, or positive pressure ventilation (Sassoon 1992). Lobar pneumonia (question 1, answer C) on ultrasound is characterized mostly by an A-B profile or by the absence of lung sliding with a B profile (Lichtenstein 2008). Primary spontaneous pneumothorax (question 1, answer D) typically occurs in young male smokers with thin body habitus and (by definition) is not secondary to underlying pulmonary disease, such as COPD, cystic fibrosis, or malignancy (Noppen 2008).
The second ultrasound image shows a lung point, which is much more specific for pneumothorax (Lichtenstein 2008). Given the patient’s dyspnea, hypoxia, and the size of the pneumothorax (from at least the second through the fifth intercostal spaces, but more likely from the apex through the fifth), the correct intervention is tube thoracostomy (question 2, answer D). This can be accomplished with either a small bore surgical chest tube or via percutaneous small-bore catheter (aka “a pigtail”) (Contou 2012, Tsai 2006). There is already enough clinical information to diagnose pneumothorax, and CT Thorax (question 2, answer A) is not required. Intravenous antibiotics (question 2, answer B) might be indicated in suspected bacterial pneumonia, but the second ultrasound image is not diagnostic of pneumonia. Non-invasive positive pressure ventilation (question 2, answer C) may be required for this patient, which is an even more compelling reason to perform thoracostomy. The ultrasound does not predict need for NIPPV, however.
As mentioned previously, lung point dramatically increases specificity (question 3, answer B) for pneumothorax (Lichtenstein 2008 and lots of other papers—this isn’t a comprehensive review). The most sensitive (question 3, answer A) finding is absence of lung sliding (or perhaps absence of sliding with augmented color power Doppler) (Cunningham 2002, Lichtenstein 2008, etc). Lung ultrasound has not yet been shown to predict either treatment failure (question 3, answer C) or mortality (question 3, answer D) in the setting of secondary spontaneous pneumothorax.
In this case, a small-bore chest tube was placed, the patient placed on bi-level NIPPV, and he did well.
Contou D, Razazi K, Katsahian S, et al. Small-bore catheter versus chest tube drainage for pneumothorax. American Journal of Emergency Medicine. 2012;30(8):1407–1413. doi:10.1016/j.ajem.2011.10.014.
Cunningham J, Kirkpatrick AW, Nicolaou S, et al. Enhanced recognition of “lung sliding” with power color Doppler imaging in the diagnosis of pneumothorax. J Trauma. 2002;52(4):769–771.
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Sassoon CS, Light RW, OHara VS, Moritz TE. Iatrogenic pneumothorax: etiology and morbidity. Respiration. 1992;4:215–20.
Slater A, Goodwin M, Anderson KE, Gleeson FV. COPD can mimic the appearance of pneumothorax on thoracic ultrasound. Chest. 2006;129(3):545–550. doi:10.1378/chest.129.3.545.
Tsai W-K, Chen W, Lee J-C, et al. Pigtail catheters vs large-bore chest tubes for management of secondary spontaneous pneumothoraces in adults. The American journal of emergency medicine. 2006;24(7):795–800. doi:10.1016/j.ajem.2006.04.006.
Ultrasound for Detection of Pneumothorax. Rebel EM (http://rebelem.com/ultrasound-detection-pneumothorax). Accessed 3/20/2015.