From the Division of Pulmonary, Critical Care and Sleep Medicine, Beth Israel Medical Center, New York, NY.
Correspondence to: Clarisse Glen, MD, Division of Pulmonary, Critical Care and Sleep Medicine, Beth Israel Medical Center, 16th St at 1st Ave, New York, NY, 10003; e-mail: firstname.lastname@example.org
Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.
A 29-year-old man with type 1 diabetes mellitus presented to our ED complaining of malaise, nausea, abdominal pain, and persistently elevated glucometer readings. This was his third visit to the ED within a week for similar complaints despite reporting full compliance with his outpatient medication. He had not had an episode of diabetic ketoacidosis (DKA) in >10 years. Review of systems was negative for productive cough, fevers, dyspnea, dysuria, or headache.
Initial vital signs were within normal limits. Physical examination revealed a calm, fatigued-appearing, thin man with normal breath sounds, absence of any rashes, and a nontender, nondistended abdomen. CBC count results were significant only for a mild leukocytosis and the metabolic profile consistent with DKA. Continuous insulin infusion and IV hydration was initiated, followed by admission to the ICU, his third admission within a week. Figure 1 is a portable chest radiograph taken on admission; it was reported as negative for any focal abnormalities.
During rounds the next morning, the ICU team elicited a report of mild, intermittent, pleuritic chest pain over the patient’s left upper chest. Examination of his left chest was negative for swelling, erythema, or tenderness. Lung ultrasonography was performed in an attempt to elucidate the cause of his pleuritic chest pain (Videos 1-3).
The finding of diffuse B lines is diagnostic of an interstitial syndrome.
An ultrasound survey of several intercostal spaces over the left lung each revealed multiple pleural line artifacts called B lines, diagnostic of an interstitial syndrome. Given the patchy and irregular appearance of the B lines, a presumptive diagnosis of interstitial pneumonia was made, followed by prompt initiation of antibiotics. A CT scan of the chest was ordered for confirmation of findings (Fig 2).
After 2 days of antibiotic treatment, the patient’s acidosis and blood glucose control improved without need for insulin infusion. Mild, residual, pleuritic chest pain persisted, and a repeat CT scan was ordered by the ward team 5 days later out of concern for the possibility of pulmonary embolism. Although no pulmonary embolism was found, the scan was remarkable in that all previous ground glass opacities had resolved (Fig 3).
This case illustrates the impact of lung ultrasonography in the diagnosis of a radiograph-occult pneumonia. Although a CT scan was used to confirm and define the extent of the findings, the lung ultrasound first detected the abnormalities that led to prompt initiation of antibiotics.
The predominant abnormality on lung ultrasound in this case was the presence of B lines. These artifacts appear distinctly different from the “A line” pattern seen in the normally aerated lung (Video 4).
Hydrostatic fluid, inflammatory exudates, or scarring involving the interlobular septa leads to a width that falls within the resolution of ultrasound, thus changing the artifact pattern in the normal lung. These interlobular septal artifacts are called “B lines” and must have the following five characteristics1-3:
Emanate from the pleural line
Move with the pleural line
Appear as discrete, ray-like, vertical lines
Extend to the edge of the screen
Erase A lines where they intersect
Although a rib interspace that reveals three or more B lines is abnormal and diagnostic of an interstitial syndrome (B pattern), one to two B lines can be found at the interspaces over normal lungs, caused either by a fissure or lung water secondary to gravity-dependent edema at the bases of the lung (B lines can often be found at the last intercostal space above the diaphragm in normal patients).
The presence of B lines was initially found to be most useful in distinguishing between pulmonary edema and COPD given that a diffuse A-line pattern over the lung surface rules out pulmonary edema as a cause of respiratory failure.4,5 Although highly sensitive for interstitial syndromes, B lines are nonspecific, given that any disorder that leads to ground glass opacities and interlobular septal thickening on a CT scan will lead to B lines on pleural ultrasound, such as in early or interstitial pneumonias, pulmonary edema, and chronic interstitial lung diseases and fibrosis.6
In this case, multiple B lines (three or more) were seen at multiple interspaces, suggestive of an interstitial syndrome (Video 5), and although the finding of such artifacts does not differentiate between hydrostatic and inflammatory causes, the global distribution pattern over the lung and associated findings can be used as follows:
1. Pulmonary edema most commonly appears as a B pattern, whereby the interspaces over the bilateral anterior chest wall reveal multiple B lines along with “sliding lung” and without any appearance of A lines, and often occur with at least small, bilateral, pleural effusions also easily detected by ultrasound. When multiple B lines are present along with A lines, this is called the X pattern, and represents a milder or resolving interstitial syndrome.7,8
2. Inflammatory causes such as ARDS or multifocal pneumonias will first present with B lines (sometimes later showing areas of alveolar consolidation on ultrasound). These B lines will usually be found either (1) without lung sliding, due to inflamed and adherent pleural surfaces, (2) unilaterally or in patches over the lung surface, or (3) with a thickened, irregular-appearing pleural line.1
The technique for diagnosing interstitial syndrome with ultrasound involves scanning the anterior and lateral portions of the chest, using a minimum of four intercostal spaces per side. On each side, the upper mid-clavicular and inferolateral, anterior axillary areas are first examined, followed by two areas at the level of the diaphragm, one midaxillary and the other in the most posterior area of the diaphragm, with the probe face pointing toward the ceiling when examining a supine patient (thus confirming probe is at the basal, posterior lung surface). An interspace that reveals three or more B lines is diagnostic of interstitial syndrome. Findings at the four points of each hemithorax are then summated to produce a complete “picture” of the lung surfaces.6,9
In Figure 2, minimum scanning points are seen in the ultrasound interrogation of a hemithorax. Combining the findings at each interspace leads to a global assessment of extent and patterns of lung abnormalities. In this case, the asymmetric (left greater than right) and patchy appearance of the B lines was most suggestive of a pneumonic process rather than pulmonary edema.
The sensitivity of ultrasonography compared with chest radiography in the diagnosis of interstitial syndromes among critically ill patients has been reported in several studies. Xirouchaki et al10 found lung ultrasonography to have a sensitivity of 98% compared with 39% for chest radiography, using simultaneous CT scans as a gold standard in a group of 42 patients in the ICU. Similarly, Lichtenstein et al11 reported sensitivities for interstitial syndromes of 98% with lung ultrasonography vs 60% with chest radiography. Given that CT scanning of patients in the ICU has obvious and much-discussed limitations, there is a diagnostic role for lung ultrasound in cases where symptoms and chest radiograph findings are discordant or where the latter are of an indeterminate nature or limited by extremes in body habitus.
This case illustrates this concept, as the patient’s admitting chest radiograph gave no hint as to the underlying reason for his recurrent DKA. The performance of bedside lung ultrasonography revealed a cause for both his symptoms of chest pain and insulin resistance.
1. Ultrasonography is a rapid and more sensitive method of confirming interstitial syndrome at the bedside than chest radiography and may used as a first-line examination.
2. Interstitial syndromes appear as B lines or vertical-appearing rays emanating from the pleural line.
3. The distribution and associated characteristics of B lines can help differentiate between inflammatory and hydrostatic causes of lung water.
Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
Additional information: To analyze this case with the videos, see the online version of this article.
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