ABSTRACT
With the increasing availability of relatively inexpensive portable, high-quality ultrasound
equipment, the use of ultrasound for needle guidance in local and regional anesthetic
techniques has become increasingly popular (1). Prior to this, nerve block techniques
relied on the use of surface anatomical landmarks to guide the introduction of the needle
with its course being gauged by the “feel” of the needle passing through fascial planes.
Confirmation of the proximity of the needle to the target nerve structures was assessed
initially by needle-evoked paresthesia but more recently by evoked muscle responses to
electrical stimulation of the nerve through the nerve block needle. However, these
techniques are “blind” and make no allowance for interindividual anatomical variability
not only in the position of the target nerves themselves but also in vital structures that are
either in direct anatomical relation with the nerve or that lie potentially in the path of the
needle. Furthermore, neither paresthesia nor nerve stimulation are a particularly sensitive
guide to needle position. The result of these deficiencies in regional anesthetic techniques
was an inevitable incidence of failure to produce sufficient analgesia and complications
related to either needle damage of the nerve or related structures or intravascular injection
of local anesthetic. In other words, even in the best hands, without the use of imaging
there is always an element of luck in regional anesthetic techniques.
