A Long Awaited Fix for a Broken Block
Ultrasound Guided Supraclavicular Approach to the Brachial Plexus
When you ask most anesthesiologists about supraclavicular brachial plexus blocks you often hear a similar story. "I learned it in training but there were a couple of near disasters so I don't use it too much any more.", translated as they NEVER use it because there is no benefit that can outweigh the magnitude of problem possible with this block.
Overall their talking about the pneumothorax that can follow inadvertently sticking a needle through the cupula (dome) of the adjacent lung which sits behind the target nerves. The pneumothorax that sometimes turns into a tension pneumothorax when the patient is placed on mechanical ventilation for the surgery which immediately follows the block during which the needle was inadvertently stuck through the cupula of the adjacent lung. The tension pneumothorax that was laid directly at the feet of anesthesia and made you look (and feel), ... well enough said. Seemingly lost amongst the hubbub of the situation was the terrific block the patient had. That's the thanks you get. This reinforces the belief that there is no block good enough to make up for the world of doodoo that comes from a problem like a pneumothorax that you caused getting it.
That this is such a common story makes one think that the problem is not just global incompetence amongst practitioners of regional anesthesia, rather there is problem with the technique of the block. The problem is obviously that the target is surrounded high-value problem areas. The dome of the lung is just behind the nerves which rest on the subclavian artery. The safest place for the needle seems to be the first rib below the nerves, which means you missed the target cleanly (but safely).
Now, match the story above with equally common stories about the supraclavicular blocks being the most solid block they've ever seen.
So why aren't more supraclaviculars done? Obviously because of the tales of woe born of attempting the block based on needling by landmark.
The inability to see exactly where the target is has made this block an outcast. Enter the ultrasound.
The ultrasound cures what's inherently wrong with this block. With ultrasound you can see the target and the areas of danger so, as long as you can control the needle you can place it on target on the first pass.
By blocking the brachial plexus in the supraclavicular space you avoid the inevitable phrenic nerve block and paralyzed ipsilateral hemidiaphragm seen with blocking the brachial plexus at the interscalene space. This can be beneficial in patients with the compromised respiratory system such as COPD or less commonly an already paralyzed contralateral hemidiaphragm.
For procedures of the upper arm and elbow this block is a simple alternative to the axillary approach (even with ultrasound guidance) requiring fewer (if any) needle re-directions to complete the block.
How to do it.
- Have the patient sitting semi-upright - sitting up lowers the venous pressure in the neck and takes any of those pesky veins out of your way,
- Use a high frequency ultrasound probe in the 5-10 cm range - The target will seldom be more than an inch (that's right 1 inch) below the skin.
- Hold the ultrasound probe in your non-dominant hand and position it "inboard" (proximal, closer to the midline) transverse to the axis of the subclavian artery.
- Use lots of ultrasound gel (always makes a better picture)
- Start your ultrasound survey above and behind the clavicle, aiming down (into the top of the chest), adjust you probe position so that you can see the dark circle of the subclavian artery. Pausing and watching the display will confirm that you are looking at an artery even without color doppler as you will see the pulse. You don't need to worry too much about mistaking the subclavian vein for the artery because the subclavian vein lies anterior (forward) of the artery and is further separated from the artery by the insertion of the anterior scalene muscle into the first rib. In addition to that, the vein lies more completely under the clavicle so the ultrasound probe must be angled to find it sometimes.
- Once you've identified the subclavian artery the nerve bundle will be found just above and behind the artery. The nerves of the brachial plexus will appear as 3-4 round dark (hypoechoic) circles in a group. The group will usually be touching the artery. The size of the individual nerves vary with the individual from 2-5mm in diameter. The nerve bundle can be followed proximally back up into the interscalene space. The arrangement of the nerves in the group becomes visibly circular as you follow them proximally, then they align vertically into a line abreast arrangement as they move between the scalene muscles.
- (If you follow the nerve group either proximally from the subclavian to the interscalene or vice versa, you may note that the artery below the nerves in the pictures looks more or less the same as you turn the corner from the neck to the shoulder. This is not the same artery, when you are at the base of the neck your looking the common carotid below the nerves and in the supraclavicular space the subclavian artery lies at the bottom of the picture. They are, many times, the same size and can look very much alike.
- Be sure to orient yourself to direction in the ultrasound picture (which direction is anterior and posterior), remember that the dome of the lung is posterior to your working area and is usually off screen. You may comfort yourself by moving the probe posterior and identifying the position of the cupula. This will reassure you that it is well out of your line of fire.
- Introducing the needle into the target area transversely to the plane of the ultrasound probe (which is transverse to the plane of the subclavian artery) allows you to advance the needle in small increments to the nerve bundle just above and behind the subclavian artery. There are perhaps 4 or 5 minor anatomical planes to cross to reach the nerves at the artery, none of these create big "pops" as you move through them.
- Identify the location of the needle tip by watching the tissue deform as you move the needle. Keep track of the length of needle you have introduced. If you lose track of the needle location, stop moving the needle and look at the angle of the probe and the needle. Make sure that the planes intersect below the skin. Adjust the probe if necessary and then back out the needle and advance it again. REMEMBER THAT EVEN THOUGH YOU ARE INSERTING THE NEEDLE AT AN ANGLE YOU'LL PROBABLY ONLY NEED ABOUT AN INCH OF IT.
- If you think your needle is in the right place or you just want to see where it is, aspirate to make sure your not intravascular (I'm not even going to mention being somewhere else) and inject a milliliter or 2 and watch the display to see where the solution is going.
- (If you feel a lot resistance, do not inject, withdraw the needle a millimeter and try again. It should never take more than moderate pressure from the thumb to inject the solution. It's unlikely you could place a short bevel needle into the nerve substance without knowing it, but you should be aware when the pressure of injecting exceeds a safe limit.)
- Adjust the placement of your needle until you're happy with the location of the local anesthetic and then continue injecting slowly and aspirating periodically. The best blocks come from even distribution and even distribution comes from slow injection.
- Depending on distribution you may want to redirect the needle once after the space has been expanded by a little volume just to make sure no unseen septum defeats the block.
- NEW 04/15/07 - PLACE SOME LOCAL BELOW THE BUNDLE IN THE ANGLE BETWEEN THE ARTERY AND THE RIB. THE ULNAR NERVE SOMETIMES HIDES OUT DOWN THERE.