A nyone who has performed blocks under ultrasound guidance has noted that some nerve targets can be completely surrounded with local anesthetic solution with volumes far below those previously thought necessary to complete a solid block. Some of the people who have used ultrasound guidance to perform blocks have actually stopped the injection when the nerve was seemingly adequately surrounded with the local anesthetic solution and then noted that the resulting the nerve block is completely effective and appears identical in every way to the block as performed with a much larger volume.
So, is it a good idea to do the same block was less volume? Is there any real benefit in modifying the block technique to base it on a smaller volume of local anesthetic?
In most cases the goal of of modifying a block technique by lowering the volume of local anesthetic injected may seem equivocal, change for change sake. But it could be argued that any time you can create the same therapeutic effect with lower doses of a drug, the proposed change would be applaudable. Less drug would theoretically lead to less side effects, the actual results would have to wait for a large study.
But in some nerve blocks the goal of lowering the volume of the anesthetic used would have a more immediate and therapeutically beneficial consequence. The interscalene block of the brachial plexus represents just such a block. According to the current results of the PSIB project study carried out by and and published here on , approximately 70% of the unintended blocks of the phrenic nerve which occur as a side effect of the interscalene block are volume related. Specifically too much volume.
So if you think the paralyzed hemidiaphragm is a bad thing, or at least undesirable in some cases, then modifying the block procedure to lower the volume used for the block would be a good thing.
As it happens, in the case of the interscalene block, nature has provided us with some anatomical assistance; a sheath fitted around the proximal portion of the brachial plexus. This tubular containment is not new. It has been available to us for most of mankind's existence it is not even newly recognized. I'm sure it was identified from nearly the earliest anatomical dissections of the human body. I'm also sure that we share this feature with many other mammalian species. What is new, is that this sheath is finally accessible, on a routine and accurate basis, by any practitioner with an ultrasound machine.
This is the basis of the Low Volume Interscalene Brachial Plexus Nerve Block. Please follow this link to the Low Volume Interscalene Block page on the Neuraxiom site to find out more about what we’re doing about it.