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The Speed of Sound

POCUS Is Not a Magic Bullet

Butts, Christine MD

doi: 10.1097/01.EEM.0000586420.30085.9c
The Speed of Sound

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A man in his 50s checked into our ED recently feeling weak, nauseated, and short of breath for two days. He had no significant medical history, and had previously been active and healthy. A fingerstick glucose at triage was higher than 400 mg/dL. He was also tachypneic, with a respiratory rate over 40 bpm. Diabetic ketoacidosis was at the top of the differential, and labs and fluids were ordered.

My senior resident decided to assess the patient's cardiac function prior to starting fluids to make sure he could handle multiple boluses. Something was terribly wrong. The images made it clear that the right ventricle was markedly enlarged and there was septal flattening. (Image 1; Videos 1 and 2 at http://bit.ly/VideosSound.) The septum could be seen flattened toward the left ventricle, a marker of high pressure on the right side of the heart. Given this new information, a CT scan of the chest was ordered, which revealed large emboli in the left and right main pulmonary arteries.

I was thinking about this case as I read the recent article “Impact of Point-of-Care Ultrasound in the Emergency Department on Care Processes and Outcomes in Critically Ill Nontraumatic Patients.” (Critical Care Explorations. 2019;1[6]:e0019; http://bit.ly/308Rin3.) The study authors divided adult non-trauma patients with a shock index into three groups: no point-of-care ultrasound, point-of-care ultrasound before fluids or vasopressors, and point-of-care ultrasound after treatment. They found that using POCUS before intervention in this retrospective cohort was associated with increased delays and in-hospital mortality.

The retrospective design is an obvious shortcoming, as is the lack of explanation about the timing of the ultrasounds. (How long did it take to do a bedside ultrasound?) The bigger issue, however, is how ultrasound is perceived in this study. POCUS is meant to augment clinical decision-making, not be a treatment in and of itself. If, when faced with a critically ill patient, the physician is uncertain about whether to give fluids or vasopressors, the use of ultrasound isn't the problem. Our history, exam, and most importantly, our clinical judgment are the bedrock of our ability to care for our patients. POCUS only serves to put weight behind our suspicions.

Our patient did in fact have DKA, but he also had multiple pulmonary emboli. His clinical picture didn't quite fit a simple diagnosis of acidosis because his pH wasn't as low as his tachypnea suggested. POCUS in this case bridged the gap between what we knew (that he had DKA) and what we suspected (that something else was adding to his presentation). Had the bedside echo been normal, we wouldn't have stopped there; we would have followed our clinical gut. POCUS is a great diagnostic weapon, but it's not the magic bullet.

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Dr. Buttsis the director of the division of emergency ultrasound and a clinical assistant professor of emergency medicine at Louisiana State University at New Orleans. Follow her on Twitter @EMNSpeedofSound, and read her past columns athttp://bit.ly/EMN-SpeedofSound.

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