Bedside B Lines

by Michael Daignault, MD


The patient with undifferentiated dyspnea always presents a unique challenge to the emergency physician (EP). That challenge is compounded when that patient becomes unstable or is crashing and the EP cannot quickly identify the problem using traditional available modalities: EMS report, talking to family, initial physical exam, STAT EKG and portable CXR, and the labs are still in progress.

Call it whatever you want – thoracic/chest/lung ultrasound… it has been around for a while, yet EPs are still unfamiliar or daunted by its readily available application to help them with the undifferentiated dyspnea patient. Its use for identifying PE (right heart strain), pneumonia (hepatization of pulmonary parynchema), and tension pneumothorax (lack of lung sliding/stratosphere sign) have been well-described.

Here, I focused on use of lung ultrasound to quickly identify pulmonary edema/acute CHF as a potential cause of dyspnea, focusing on its advantages over traditional modalities.

An all too-common clinical scenario: 60 YO M with PMHx of DM, HTN, COPD/asthma (not on home O2) and ESRD on HD who presented from home with acute dyspnea. EMS noted a very high BP, 220/100. Initial lung auscultation revealed reduced air movement bilaterally (“tight chest”) with scant expiratory wheezing. O2 saturation was 89%. Portable CXR was interpreted as “unremarkable.” Treatments with albuterol/atrovent and IV methylprednisone were stared for presumed COPD/asthma. Patient noted interval improvement, but on reassessment began to acutely decompensate. The resuscitation team was setting up for rapid sequence intubation; thankfully an ultrasound machine was bedside. Using the phased-array “cardiac” probe, the team leader placed visualized something close to this:

With the probe held in place and slightly rocked from side-to-side multiple shimmering lines such of these were seen extending from the pleural line extending all the way down to the bottom of the screen. Known as “b-lines,” they represent interstitial fluid, or pulmonary edema, and are pathological.

To qualify as a B-line, the following criteria should be met:

  • Extending from the pleural line (the line between 2 ribs as the probe is placed in the intercostals space) all the way down to the bottom of the screen.
  • There must be a lot of them. There has been many research studies, too numerous to mention here, in attempts to quantify the number of B-lines needed to qualify as pulmonary edema. 1 or 2 B-lines are considered either normal or mild pulmonary edema; what we care about is when there are many lines, too numerous to count. If there are 1-2, and your patient is crashing, odds are that acute pulmonary edema is not the cause.
  • The B-lines must “erase” physiological A-lines, which are reflections of the pleura line and are seen in a “normal” lung ultrasound here:

The team recognized the aforementioned, applying  BiPAP and giving an IV dose of Lasix, with steady improved. By the time the lab tests came back the patient was feeling much better… BNP was >3000 .

This scenario is interesting  and common – lung ultrasound was more useful than traditional lung auscultation and CXR, both of which lagged the real-time ultrasound results.

The lesson learned for us was to not wait next time to grab the ultrasound and put the probe on the patient. And secondly, to not use the lung ultrasound as a last resort, but as part of the initial physical exam to quickly differentiate the cause in an acute dyspneic patient.

Sources for images:

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