After posting about the current face-off between the old-school stethoscope and the new kid on the block, POCUS, I reached out to Dr. Omar Darwish. As the coordinator of the UC Irvine SOM Point-of-Care Ultrasound elective I was certain he could offer some invaluable words of wisdom. He did not disappoint...but he did hit me with a few surprises. See below for his essay on this hot topic.
The medical field is becoming increasingly reliant on technology for diagnosis. A patient presents with syncope and many will automatically order an echocardiogram. Why is this? One explanation is that some think heart auscultation is not sensitive enough to pick up the sound of a murmur. This issue may be quite fundamental to the person trying to make the diagnosis: if you want to be good at cardiac auscultation, you need to be driven to improve your cardiac physical exam skills. If you don’t have the desire to learn the cardiac exam, you won’t be able to hear a murmur. Syncope, a cardinal symptom of aortic stenosis, can be ruled out with high confidence by simply listening to the heart with your stethoscope. This was demonstrated in a study where third-year medicine residents and staff internists examined 124 consecutive hospital patients who had been referred for echocardiogram. They each were able to use cardiac auscultation to identify the presence of aortic stenosis in 68/69 patients. The patient they missed was in heart failure and had pulmonary edema on chest X-ray, but the physicians were blinded by the patient’s history and chest X-ray findings (1). So, if you do not hear a murmur, it is very unlikely that clinically significant valvular disease is present and even less likely if you have history, EKG, and imaging results that are not supportive of an underlying cardiac process. Determining if your patient has severe aortic stenosis is a different question. If you hear a murmur, particularly with other features (e.g. soft S2, weak carotid pulse, slow upstroke), an ultrasound should then be performed. But if you want to be efficient, it is best that you learn how to use your stethoscope than to run around with an ultrasound probe looking for a murmur in each of your patients who present with cardiopulmonary symptoms.
On the other hand, auscultation of the lung has shown not to be sensitive, but specific. A study comparing lung auscultation, chest radiography, and lung ultrasound was done on 32 ventilated patients with alveolar consolidation, alveolar-interstitial syndrome, and pleural effusion.2 The specificity for each of these pathologies was 90, 100, and 90%, respectively, and was comparable to chest x-ray and lung ultrasound. However, sensitivity for lung disease with auscultation was shown to be poor at 42% for pleural effusion, 8% alveolar consolidation, and 34% alveolar-interstitial syndrome (2) On the other hand, sensitivities for these pathologies with lung ultrasound were increased to 92%, 93%, and 98%, respectively.
Purely based on these small studies, one can conclude that the stethoscope is very good at ruling out aortic stenosis, but poor at ruling out pulmonary disease.
That said, the diagnostic power of any study is based on your pretest probability. Let’s say you have a patient presenting for their yearly physical exam. They swim daily with no pulmonary symptoms and have clear breath sounds on lung auscultation. Should you slather some gel on your hand-held ultrasound probe and look for lung pathology?
The question shouldn’t be whether POCUS should replace the stethoscope. The real question should be: how can we integrate POCUS into our diagnostic approach to a patient?
Optimal use of POCUS relies on two things, (1) having sound medical knowledge and (2) having sound history and physical exam skills
1. Etchells E, Glenns V, Shadowitz S, Bell C, Samuel S. A Bedside Clinical Prediction Rule for Detecting Moderate or Severe Aortic Stenosis. J Gen Intern Med 1998;13(10): 699-704.
2. Lichtenstein D, Goldstein I, Mourgeon E, Cluzel P, Grenier P, Rouby J. Comparitive Diagnostic Performances of Auscultation, Chest Radiography, and Lung Ultrasonography in Acute Respiratory Distress Syndrome. Anesthesiology 2004;100:9-14.