Only in the past decade or so has research on functional regional
anesthesia anatomy, outcome, and equipment slowly begun to transform
regional anesthesia into a modern discipline. However, in many ways the
equipment used for peripheral nerve block remains in its infancy. The
sophistication and functionality of the equipment used for peripheral nerve
blocks (PNBs) are, at best, rudimentary and lag far behind those of general
anesthesia, as depicted in the following examples.
Monitoring the Depth of Needle Insertion
Spinal cord injury after interscalene block is perhaps the most serious
complication of a PNB. This devastating complication, however, can occur
only with an excessively deep needle insertion (ie, >2.5
cm).1 Monitoring the depth of the needle insertion is
substantially important to avoid a too-deep insertion (eg, spinal cord or
chest cavity with interscalene block).
In fact, the recently suggested standardized block documentation procedure
requires clinicians to document the depth at which the needle is inserted.
Nevertheless, most commercially available needles still do not have depth
markings for such objective documentation.2 Despite that fact, there is much
work underway to remedy this deficiency, and it is inevitable that all
needles used in regional anesthesia will eventually incorporate depth markings on their
Current Delivery & Disconnect Monitoring
Nerve stimulator–assisted nerve localization has become a standard
technique in PNB. In contrast to paresthesia techniques, nerve stimulation
provides a more objective assessment of the needle position in relation to the
nerve, does not require patient cooperation, and permits the use of
sedatives and analgesics for patient comfort during a nerve block procedure.
The basic premise of the nerve stimulator–assisted nerve blocks is that the
electrical current (“field") in front of the advancing needle should elicit
a motor response before the tip of the needle enters the nerve. In many
nerve block techniques, a functioning nerve stimulator is essential to
decrease the risk of
inadvertent placement of the needle intraneurally or intravascularly. For
instance, because of the close proximity of the subclavian artery anterior
and inferior to the brachial plexus during cervical paravertebral block, the
functionality of the nerve stimulator is of paramount importance to avoid
vascular complications.3 With a functioning nerve
stimulator, a motor response of the shoulder muscle is seen when the
brachial plexus is stimulated, which should occur before the subclavian
artery is punctured by the advancing needle. In the case series on continuous
paravertebral blocks using a stimulating catheter reported by Boezaart et
al.,3 vascular complications consisting of large-vessel
puncture with a 17-gauge needle occurred only in patients in whom the nerve
stimulators were found to be malfunctional.
Consequently, the ability of the nerve stimulator to deliver accurate
current output and integrity of the stimulator-needle-return (skin)
electrode circuit is of utmost importance for both the block success and the
safety of the procedure. Problems with the reliability and accuracy of nerve
stimulators have long been recognized ...