The Stethoscope of the Future: Bedside Ultrasound
July 31, 2014
The applications of bedside ultrasound have gone well beyond scanning the gallbladder . . . to the lungs?
It is a typical Monday night in a university emergency department. The list of “To Be Seen” patients has doubled since 6pm and the ambulance dispatch phone has not stopped ringing. As your staff is furiously typing away, dictating their notes and clicking on the various buttons in your EMR, you wonder how any patients are actually going “to be seen” if everyone is sitting in front of a computer screen.
One of your eager junior residents peels himself away from the computer just long enough to inform you he has a few patients to tell you about. He finishes checking all of the boxes in his chest pain order set and turns around to face you. “I have three patients that are ready for disposition” he gushes. The first is a 70-year-old diabetic female who is having chest pressure that is concerning for unstable angina. She doesn’t need an emergent cath right now, but she has a TIMI score of 3 thus far and will need admission for further evaluation. The second one appears just as easy. He’s a 30-year-old otherwise healthy young man who checked in because he wanted his lateral thigh abscess drained.
Your resident is confident that he’s about to complete his hat-trick until about halfway through his third presentation. The last patient is a 50-year-old male who came in tonight because of worsening cough and fevers. His kids have been sick with a bad cold and he thinks he’s contracted something from them. He’s been coughing for a few weeks now, and over the past few days, he’s been having worsening fevers and chills. He’s mildly tachycardic, and has an oxygen saturation of 96% on room air per the vital signs in the computer. His blood pressure and respiratory rate are documented as normal, and his temperature is 38.0°C after taking some acetaminophen prior to arrival. You listen patiently as your resident wraps up his presentation and shows you the azithromycin prescription and discharge paperwork ready to go for this last patient.
“I’m sorry, I didn’t catch what his lungs sounded like…” you interject. With a sheepish look, your resident responds, “I couldn’t hear very much. His exam was limited by his body habitus.” “Oh and he doesn’t want an X-ray because he is rushing to get out of here and just wants a prescrip- tion for antibiotics anyway.” You decide this might be the perfect case to do some good bedside teaching, so you ask your resident to go with you to talk to the patient. You figure you can show your young apprentice how you like to educate patients about viral versus bacterial infections, and review symptomatic regimen options with him and the patient. Just for good measure, you grab your trusty ultrasound machine since you almost feel naked walking into a patient’s room without it these days.
As soon as you enter the room, the warning bells start going off in your head. The 50-year-old male in front of you looks like he’s lived a hard 50 years. His fingers are yellowed from years of smoking (despite his response of “nope” when he was asked if he smokes) and his respiratory rate that was documented as “16” is more than twice that at present. He is morbidly obese so your physical exam is indeed limited, but you think you hear some relatively diminished breath sounds and faint crackles at the bases of his thorax. To improve your exam sensitivity you demonstrate to the patient how you want him to breathe – “breathe like this” you say as you take a rapid full tidal capacity breath in, then out without making any unnecessary noise with your mouth and nose. You get a better exam but are even more convinced afterwards that something sounds wrong.
1: Right Posterior Thorax
“How long is this going to take, doc?” the patient asks as you finish listening to his lungs. “I have a thousand things to do tonight and just need some antibiotics for this nasty virus I got.” “Not long” you say as you start your bedside thoracic ultrasound and show the patient and your resident a view of the right posterior thorax (Image 1). For comparison, you slide your probe a few rib spaces lower and capture another picture (Image 2). What do you see on ultrasound? What’s the patient’s diagnosis?
2: Below Right Posterior Thorax
3: Right Lower Thorax
As you scan through the patient’s thorax, you show the patient the consolidated lung tissue in his right lower thorax (Image 3) and compare it to the echotexture of the dense liver just below the bright white diaphragm (Image 4).
4: Echotexture of dense liver
You note that the lung appears grossly abnormal on ultrasound and explain that there’s a pretty significant pneumonia brewing in there. Upon further inspection, it looks like there is a consolidation in the left hemithorax, as well. You scan systematically through all of the lung fields to make sure you aren’t missing anything that requires emergent intervention. The patient’s evolving tachycardia, tachypnea, bilateral pneumonia, and inherent risk factors move you to recommend further blood work, a chest x-ray, and inpatient observation and antibiotics. After seeing the ultrasound images, the patient (and your resident) see the wisdom of your ways and the hospitalists happily bring the patient in for further treatment.
As you walk back towards the computers with your resident, he wraps his stethoscope around your neck. “What’s that for?” you ask. Your newly inspired resident quips back “What do I need that old thing for? Ultrasound is clearly the stethoscope of the future…”
* * *
Pearls and Pitfalls for Thoracic Ultrasound
1. More and more health care practitioners are learning how to incorporate thoracic ultrasound into the evaluation and management of patients. Thoracic ultrasound is now being used to diagnose pneumothoraces, pneumonias, interstitial edema, masses, pleural effusions, empyemas, etc.
2. To perform a thorough thoracic ultrasound, utilize both a high frequency transducer to evaluate the superficial structures, and a lower frequency probe to scan through deeper structures.
3. In normal patients, a thoracic ultrasound will demonstrate a hyperechoic pleural line just farfield between two hypoechoic rib shadows. The large acoustic impedance between the pleura and underlying aerated lung parenchyma typically creates horizontal white reverberation artifacts known as “A lines”. Vertical white lines extending off the bright white pleura are known as “B lines”. These comet-tail artifacts arise when there is a prominent alveolar-fluid interface and will typically erase A lines (Image 5).
5: B lines, with A lines erased
4. In patients who have pneumonia, the edematous and inflamed lung parenchyma will start to demonstrate an echotexture similar to that of liver tissue on ultrasound. This “hepatization” of the lung will be seen in areas of consolidation throughout the thorax (Image 3).
5. Consolidated lung from pneumonia will typically have dynamic air bronchograms that will appear as multiple bright white, hyperechoic regions speckled in between the lung parenchyma. The presence of dynamic, moving bright white air bronchograms helps to rule out obstructive atelectasis.
6. If you see lung hepatization, look at the costophrenic angles on ultrasound. You may find an associated parapneumonic effusion or empyema which may require drainage.
7. Thoracic ultrasound is all about pattern recognition and understanding the ultrasound artifacts that arise from different interfaces within the thorax. Scan through the normal regions of the patient’s lung to obtain a baseline for comparison. Use ultrasound in conjunction with your history and clinical findings to assist in the diagnosis and management of patients presenting with cardiopulmonary complaints.
8. Practice, Practice, Practice: The best way to minimize errors is through experience, so scan lots of normal anatomy. The more scans you do, the better you will be able to differentiate abnormal from normal, even when you may not be sure exactly what the abnormality is.
Teresa Wu (@TeresaWuMD) is an Associate Professor and Simulation Curriculum Director at the U of A-College of Medicine-Phoenix. She is the Director of the Ultrasound Program & Fellowships for the Maricopa EM Program and the creator of the app SonoSupport.