Emergency Medicine News:
The Speed of Sound
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. Follow her @EMNSpeedofSound, and read her past columns at http://bit.ly/ButtsSpeedofSound.
Mistakes can (and will) occur even if you are aware of the pitfalls of traditional approaches for placing central lines. A carotid artery puncture sounds like a disaster, but this may not cause a significant complication if it is recognized before insertion of the dilator. Traditional methods, such as analysis of the pulsatility and color of the blood obtained on aspiration, however, may be inaccurate and misleading. Patients who are hypoxic or hypotensive may not demonstrate bright red, pulsatile blood flow when the artery is punctured.
Ultrasound can be used to confirm that the vein has been punctured before placing the dilator. It should be used to guide the needle directly as described in prior months' columns. (Read these in Dr. Butts' collection on our website: http://bit.ly/ButtsSpeedofSound.) Once the flash is obtained in the syringe, most operators tend to remove the ultrasound from the field and complete the procedure blind. The operator is holding the needle to place the guide wire, however, and even slight movements of the needle may cause it to be dislodged from its original position. Michael Blaivas, MD, and colleagues described such a case in an analysis of six cases of accidental arterial cannulation in which the needle tip was theorized to have migrated deeper from its original position prior to wire insertion. (J Ultrasound Med 2009;28:1239.)
Instead of putting the transducer to the side after the flash is obtained, the transducer can be reapplied to the field once the guide wire is ready to be inserted. Using this technique, the guide wire can be directly visualized entering the vein (Image), further confirming correct placement. If this technique proves to be too cumbersome for the practitioner working alone, the transducer can be reapplied to the field once the wire has been inserted. The wire should be confirmed to be traveling within the vein, proximally toward the chest, prior to dilation.
As emergency physicians, we are taught that we should avoid relying on a single method of confirming successful endotracheal tube placement. We are taught to use direct visualization, lung sounds, end-tidal CO2 monitors, chest x-ray, and even ultrasound to ensure that the tube is in the trachea before feeling secure in our placement. Perhaps we should use a similar method when placing central lines, prior to placement of the dilator, to prevent the potential catastrophe that may result from arterial dilation.
Using the standard method of observing the character of the blood aspirated could be compared with direct visualization of the tube passing through the cords. Using ultrasound to confirm wire placement, manometry, and blood gas analysis could be considered adjunctive measures. Using a combination of these techniques may even further improve the safety of a procedure that has become safer by the use of bedside ultrasound.
Tip of the Month
When evaluating patients for suspected gallstones, some stones may be lodged in the neck and be tough to see. Have the patient roll onto his left side and check again. This will often reveal “hidden” stones.
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