Emergency Department Diagnosis of Pneumothorax Using Goal-directed Ultrasound

A 23-year-old female with a history of fibromyalgia and recurrent back and neck spasms presented to the emergency department (ED) complaining of right-sided upper back and chest pain with associated dyspnea. She had just received trigger point injections to her upper back and neck, performed by a pain management specialist. The symptoms developed immediately following the procedure, as she was leaving the physician’s office.

Medication history included Ortho Tri-Cyclen and as-needed Darvocet. Her initial vital signs in the ED were blood pressure 99/69 mm Hg, pulse 97 beats/min, respirations 24 breaths/min, temperature 98.9°F, and oxygen saturation of 93%. On examination she appeared to be in obvious pain, with splinting noted during respirations. She had clear speech, no jugular venous distention was noted, and her trachea was midline with no neck or chest wall crepitus. She had no heart murmurs and a rapid but regular heart beat. On lung auscultation it was felt that she might have decreased breath sounds on the right, but the exam was limited by the patient’s refusal to take deep breaths due to the pleuritic nature of her pain. The extremity exam revealed no dependant edema, no calf tenderness, negative Homan’s sign, and normal distal pulses and capillary refill bilaterally.

An electrocardiogram revealed sinus tachycardia at a rate of 105, with no evidence of right heart strain. Goal-directed bedside sonography was performed by the emergency physician, who noted an absence of pleural sliding on the right with a definitive lung point. The chest x-ray was completed while the physician prepped for needle aspiration of the pneumothorax. Needle aspiration was completed successfully without complication and the patient was admitted to the cardiothoracic surgery service for observation.

Discussion

This patient presented with concern for possible pulmonary embolism versus pneumothorax. Her diagnosis was quickly made via focused bedside ultrasound. If no pneumothorax had initially been noted, the physician could have quickly moved on to a focused exam for deep vein thrombosis or evidence of right heart strain. The use of ultrasound to diagnose pneumothorax was first described in Europe by intensivists. Using a linear or curvilinear array transducer in the sagittal position, beginning in the second to fourth midclavicular intercostal spaces in a supine patient, one looks for the absence of normal pleural sliding.^1,2 From this starting point, the exam should be carried out as far laterally as the midaxillary line. Whereas the supine chest x-ray has a sensitivity of 36% to 75% for detecting pneumothorax, the sensitivity of ultrasound in the detection of anterior pneumothoraces has been found to be 92% to 100% based on studies using computed tomography as the criterion standard.^1,3,4 The finding of a lung point, which is the transition point from the absence of normal pleural sliding to its presence as the pneumothorax ends, is 100% specific for pneumothorax² (see Video Clip S1 available as supporting information in the online version of this paper).

Normal pleural sonographic artifacts that should be noted are comet tail artifacts (B-lines) originating along the pleural interface and the presence of A-lines (Figure 1). The comet tail is an important reverberation artifact that is absent in the presence of a pneumothorax. These appear as hyperechoic laser-like reverberations that project down from the pleural interface through the depth of the image. Comet tails move along the pleura with respiration and vary in width and appearance in real time. These B-lines also will cover up the A-lines and are at times more prominent in certain patient populations, such as those presenting with congestive heart failure. The A-line is a horizontal reverberation artifact noted at twice the distance from the skin to pleural interface. A-lines may be seen in normal lung or in the presence of a pneumothorax. Using M-mode (motion mode), the practitioner may see a seashore sign, which is an irregular tracing at the depth of the pleura due to normal lung sliding (Figure 2). The abnormal stratosphere sign is seen in M-mode as a smooth motionless baseline when a pneumothorax is present and lung sliding is absent (Figure 3). An additional finding called the power slide can be seen when a power Doppler signal is noted at the site of normal pleural sliding (Figure 4). In the presence of a pneumothorax, a power Doppler signal would be absent.^2,3

Figure 1.  A-line and comet tail artifacts.

Figure 2.  Seashore sign.

Figure 3.  Stratosphere sign.

Figure 4.  Power slide.

Although focused bedside sonography can be very useful for detecting pneumothoraces, the examination does have its limitations, and in certain instances the diagnosis may be missed. A small apical or perimediastinal pneumothorax can be missed, and failure to perform the exam with the patient in a supine position can decrease its sensitivity, as free pleural air might not collect in the anterior chest where it is likely to be detected using ultrasound. It must be noted that a lung point may not be visualized in very large pneumothoraces, where there may be no lung contact with the chest wall, or if the sonographer fails to scan a significant area of the chest wall to identify the borders of the pneumothorax. Any pathology outside the actual scanned region of the chest wall will obviously be missed by ultrasound. Finally, it is worthwhile to note that conditions like pleural adhesions, blebs, a right mainstem intubation, and others can result in the absence of lung sliding.