Ultrasound Tip #2
COLOR FLOW
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I don’t make as much use of Color Flow as I could while doing blocks routinely unless I am teaching a concept to a student or a new assistant and I have the luxury of extended time. Typical uses of color flow, like identifying vessels, I usually don’t bother doing. I can more quickly recognize them by pausing (to recognize arterial pulse) and altering pressure (to recognize compressibility), or I just alter my plane so that the ‘possible’ vessel is no longer in my path. I am not recommending these tools to anyone that does not have extended knowledge of and history with ultrasound use. I have, however, been greatly assisted by this tool on a few occasions when things have gotten complicated. Here are some other novel and helpful tricks that you can use color flow for that can be helpful when you have a less than ideal image.
The first example is when you are doing a deep block and have a steep needle angle or are out-of-plane, and it is not completely clear where you needle tip lies. Again, sometimes a shallow block may be helped along when the needle tip has become difficult to locate. If nerve stimulation has failed you (like with an anterior sciatic) or you just don’t want to keep moving your needle about to identify the position (patient discomfort or coagulopathy concern), using an advantage of ultrasound, you can inject a little local anesthetic to give you a hint. Well, with a bad machine or just an unclear or distorted image (replacing a failed block), this little bit of local may not be adequate to demonstrate your position. You could just keep giving a little more, but this may take multiple boluses which depletes your needed volume for a successful block and can get you into trouble with toxicity from the total volume that you end up needing to give or with the ultimate realization that you are injecting into a vessel or into macerated tissue.
Turning on color flow in this circumstance will allow you to more easily recognize the location of your small injection and allow you to ultimately be more judicious with your needle movements. A small but quick injection is optimal to recognize the burst of color at the needle tip due to flow and tissue displacement. You may also note a color burst that extends the length of the needle as the local fires up this low area of resistance. Keep that image in your mind if the angle of your needle is not well visualized.
This can be helpful as well if you are just trying to quickly recognize if you are beyond a fascial layer or not. An example here is when you want to determine whether you have advanced just beyond the SCTL or not when doing a paravertebral block. If you see a flash below the SCTL, then that ‘pop’ that you felt WAS real, and you are in. Another is to see if your needle during a femoral block is under the fascia iliaca (or incorrectly causing flow above the femoral artery). This may also be helpful to detect ‘dual flow’ above AND below a plane which may happen when utilizing nerve stimulation as an end-point, especially with a sharp-beveled needle. In this circumstance, the relatively long and sharp distal tip barely crosses the fascia iliaca, for example, and the injection leads to local anesthetic spreading above and below the fascia iliaca. The stimulation ceases due to some amount of local covering the femoral nerve, but the spill above the plane is difficult to recognize. Color flow could help confirm this sooner if it is in question.
I have also used color flow to help me determine when I am in the plane between the adductor magnus and gluteus maximus during an anterior sciatic on a morbidly obese patient who was having trouble recognizing when the pulse went from her inner thigh to her buttocks. I turned on color flow to help accentuate contractions from the direct muscle stimulation between the two muscles. I was also able to see a longitudinal ‘flash’ of color with my injection after I made my best determination of my position. This flash represented the local flowing between the muscular planes (where the sciatic nerve resides) medially and laterally further confirming my correct position.
Color flow is one more tool that can help you become more effective and safe as you continue to expand the use of ultrasound in your practice.
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