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Emergency Medicine News:
doi: 10.1097/01.EEM.0000434479.81159.50
The Speed of Sound

The Speed of Sound: Assessing Fluid Need with Doppler of the Brachial Artery

Butts, Christine MD

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Dr. Butts is the director of the division of emergency ultrasound and a clinical assistant professor of emergency medicine at Louisiana State University at New Orleans.

Treating hypotensive patients can be challenging for even the most experienced emergency physician. Patients are often unable to give any history, and the physical exam may give only limited clues about the cause of the patient's condition. The EP may feel hesitant to administer fluids in older patients or patients with known pre-existing cardiac disease. Invasive monitoring is the gold standard for determining a patient's fluid status, but requires significant time for insertion, and carries the risk of iatrogenic injury to the patient. Ultrasound can rapidly give the EP a wealth of information and guide treatment.

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Ultrasound of the inferior vena cava (IVC) (and thus, central venous pressure [CVP]) can serve as a marker to predict responsiveness of the hypotensive patient to a fluid challenge. The IVC and CVP have been widely studied, with conflicting opinions about usefulness and reliability.

Ultrasound of the brachial artery Doppler waveform has been proposed as a method of identifying patients who will benefit from fluid administration. This technique proposes identifying the brachial artery in the antecubital fossa with ultrasound and generating a Doppler waveform. (See images.) The waveform is then analyzed over a respiratory cycle to determine the maximum and minimum peak velocities. Utilizing these values, the equation {(Vmax-Vmin) / [(Vmax+Vmin)/2]} x 100% can be used to generate a percentage.

A 2009 study evaluated these calculations in mechanically ventilated patients in an ICU, specifically those pending fluid administration secondary to “acute circulatory failure” (hypotension, oliguria, need for pressors, etc.). (Crit Care 2009;13[5]:R142.) The authors hypothesized that they would be able to separate the patients as responders (those with improvement in their hemodynamic parameters with fluids) or non-responders (those with little improvement with fluids). They compared their measurements obtained with ultrasound with invasive arterial monitoring, which allowed them to calculate stroke volume and stroke volume index directly.

Patients who had brachial artery pulse variation greater than 10% were responders, and would demonstrate an increase in stroke volume after fluid administration. Patients who had variation of less than 10% were non-responders, and did not demonstrate a reliable increase in stroke volume with fluids.

The technique may seem daunting to a beginning sonographer, but it is promising and adds an additional tool for the EP to evaluate hypotensive patients and to plan rapid treatment.

Figure. Doppler wave...
Figure. Doppler wave...
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* Read Dr. Butts' past columns at http://bit.ly/ButtsSpeedofSound.

* Comments about this article? Write to EMN at emn@lww.com.

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Questions? We Have Answers

Have an ultrasound question? A topic you'd like to see in future Speed of Sound columns? Send your questions and suggestions for Dr. Butts to emn@lww.com.

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© 2013 by Lippincott Williams & Wilkins

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