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The Speed of Sound

The Speed of Sound

In Defense of the IVC

Butts, Christine MD

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doi: 10.1097/01.EEM.0000531130.08756.2d
    inferior vena cava, ultrasound
    inferior vena cava, ultrasound:
    A long axis view of the IVC in a hypotensive patient. This IVC is small with almost full collapse during a long axis view of the same IVC after fluid bolus. Note that it has increased in size. Watch a video of this at http://bit.ly/VideosSound.
    Figure
    Figure

    The IVC needs a new PR agent.

    It was all the rage a few years ago. Faced with a hypotensive patient, assessment of the IVC was the way to go. Slowly, the tide began to turn. First, its utility in ventilated patients was questioned. Then, it was found that the IVC wasn't good at predicting overall fluid status. The result? Ultrasound assessment of the IVC has fallen out of favor in many circles, and we've moved on to the next big thing. I don't think, however, that it's time to give up on the IVC.

    Evaluating the IVC is an easy technique. Unlike some other indicators of fluid status, which may require the use of Doppler or precise cardiac views, the IVC can be easily assessed from the subxiphoid region. Beginning sonographers typically learn this cardiac view first. A simple tweak of the hand to point the transducer straight down toward the spine, with the indicator pointing toward the patient's head, will typically expose the IVC. Moving the transducer slowly to the patient's right is often helpful if it's not immediately visible.

    The IVC can usually be found, even when other factors make it challenging. Cardiac views can be challenging in obese patients, and ribs can make the view tough even in thin patients. This is to say nothing of examining a sick or intubated patient, but the IVC can almost always be found in these challenging patients from the subxiphoid view or the right flank, using the liver as a window. The transducer, when placed in the right mid-axillary line with the indicator pointing toward the patient's head, can be fanned from anterior to posterior until the IVC is seen deep to the liver.

    Figure
    Figure:
    A long axis view of the IVC in a hypotensive patient. This IVC is small with almost full collapse during respiration. Watch a video of this at http://bit.ly/VideosSound.

    The IVC can also yield valuable information, such as the central venous pressure. The size of the IVC and the percent fluctuation with respiration in a nonintubated patient allow for an estimate of this value. One of the most crucial aspects of evaluating hypotensive patients is determining the type of shock present. A look at the heart and IVC can quickly take cardiogenic or obstructive shock off the table. These diagnoses require different treatments from hypovolemic or distributive shock, and this can be life saving for the patient. The IVC is part of the puzzle in this case. Poor cardiac function with a distended IVC? Supports cardiogenic shock. Pericardial effusion with distended IVC? Supports obstructive shock.

    The IVC might not be good at predicting who will improve with fluids, but it can give some sense of fluid tolerance. One thing that seems fairly clear: Too much fluid is bad for our patients. Knowing when to stop is vital. An IVC that goes from flat to full may be a sign that it's time to stop fluids.

    The IVC isn't the magic bullet it was once thought to be, but it still has a role in our bedside assessment.

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