Case #5: Shortness of breath
HPI: 89 year old male with history of afib, HTN, HLD, pulm HTN, CAD, CHF presenting with two days of palpitations and increasing shortness of breath with substernal chest pain. CXR seen below:
Read as: “Increased perihilar and basilar airspace opacities along with likely small pleural effusions.”
What is the sensitivity and specificity of CXR in detecting pleural effusion? How about US?
Position patient in the sitting position where the most dependent area will be the costophrenic angle. Using the transabdominal probe, position the indicator probe towards the patient’s head and place in the midaxillary line towards the bottom of the rib cage so as to obtain a sagittal view.
This is a similar view to the RUQ scan during the FAST exam but the landmarks are slightly different in that you do not need to identify the kidney. Identify the liver, the diaphragm and the thoracic cavity. Additionally, you should be able to see the spine in the far field and as the patient breathes, you can identify the echogenic lung within the effusion if one is present.
One notable sign found with pleural effusions is the “spine sign” in which the hyperechoic line of anterior spine can be seen extending into the thoracic cavity. In a normal healthy person, the spine sign will stop abruptly at the level of the diaphragm as the healthy air filled lung does not allow for sufficient conduction to see the spine in this area. Fluid is an excellent conductor and allows the sound waves to travel and reflect off of the thoracic spine.
Chest X-rays are able to detect 50ml of fluid on a lateral upright film, however in the Emergency department a single AP view is what is obtained. Blunting of the costophrenic angle is not appreciated until at least 200cc of fluid has collected. This leads to a sensitivity of 78.4% and specificity of 76.4% compared to CT scan (Brixey et al, 2011).
In contrast, bedside ultrasound has been proven to detect 20ml of fluid reliably with one meta analysis demonstrating a sensitivity of 93% and specificity of 96% compared to CT scan (Soni et al, 2015).
A thoracentesis is still needed for complete characterization, however thoracic ultrasounds may be utilized to identify pleural effusions as illustrated in this case. One study suggests that you may be able to characterize the effusion based on ultrasonographic findings.
An effusion seen in conjunction with B-lines on ultrasound is highly suggestive of a transudative etiology secondary to congestive heart failure. If complete lung consolidation is appreciated on ultrasound, it is can be concerning for malignancy(Prina et al) in addition to pneumonia, pulmonary edema, etc.
Bedside ultrasound in the Emergency Department has an ever growing list of applications. In the thoracic ultrasound we see a more reliable modality for detecting effusions than the traditional x ray. It is nearly as sensitive and specific as the gold standard CT at a fraction of the cost and time. It is a valuable tool to have in the Emergency Medicine Tool box.
References:
1. Brixey AG, Luo Y, Skouras V, Awdankiewicz A, Light RW. The efficacy of chest radiographs in detecting parapneumonic effusions. Respirology. 2011Aug;16(6):1000-4.
2. Soni NJ, Franco R, Velez MI, Schnobrich D, Restrepo MI, Mayo PH. Ultrasound in the Diagnosis and Management of Pleural Effusions. J Hosp Med. 2005 Dec 10(12): 811-816.
3. Prina E, Torres A, Carvalho CRR. Lung ultrasound in the evaluation of pleural effusion. J Bras Pneumol. 2014 Jan-Feb, 40(1): 1-5.
Happy Learning!
Emma Burch MD