Visualizing Peripheral Nerves Using Ultrasound-Guided Approach

The nerves of the upper extremities derive from the brachial plexus, and likewise, the nerves of the lower extremities derive from the lumbo-sacral plexus (1). In clinical practice, nerve blocks are commonly performed to provide postoperative analgesia after orthopedic procedures involving the upper and lower extremities (2,3). They may also be used as a sole anesthetic technique during surgery.

The two main concerns with upper and lower extremity blocks, as with other regional anesthetic techniques, are technical failure and block related complications. The most cited complications are bleeding from inadvertent arterial or venous puncture, intravascular injection of local anesthetic resulting in central nervous system or cardiac toxicity, and intraneural injection of local anesthetic resulting in peripheral neuropathy of varying degrees (4,5).

Both technical failures and complications are related at least in part, to the fact that all the techniques used to date are blind. Anatomical landmarks (as described in the literature) and nerve stimulators are helpful ways to localize the nerves to be blocked.

We believe that the best approach to improve success rate and minimize complications of peripheral nerve blocks is to use image-guided techniques. In the last few years, different imaging modalities have been used to evaluate the peripheral nerves of the upper and lower extremities. Studies currently underway at our institution seek to develop a comprehensive technique for upper and lower extremity nerve blocks. However, this involves anesthetizing from the top of the limb in order to numb the entire extremity. More research is needed to derive a comprehensive examination of the peripheral nerves found in the lower regions of the upper and lower extremities. While CT scanning and MRI are probably the techniques of choice when it comes to diagnosing nerve pathology, they would not be useful in the perioperative setting due to the lack of portability and the inability to perform real time imaging simultaneously with nerve block performance (6,7).

Ultrasound has been used successfully in the last few years to image the peripheral nerves of the upper extremity (8,9). The development of higher frequency ultrasound probes, and higher imaging resolution has made it possible to localize and evaluate peripheral nerves with ultrasound, something that was not possible only 10-15 years ago. The anatomy of the brachial plexus has been described by a number of authors. There have been some preliminary studies looking into the possibility of developing a real-time ultrasound guided technique for upper extremity blocks (10, 11, 12, 13,). Studies performed at our institution involving refining a technique for upper extremity blocks show encouraging results.

It is clear, that ultrasound can be used to a further degree of sophistication in order to image peripheral nerves in the lower parts of the upper and lower limbs. As expressed by many of the referenced authors, ultrasound use is likely to increase significantly in the coming years, both in the areas of diagnostic radiology and clinical regional anesthesia, to guide nerve blocks (17). As a result, it is evident that the development of an advanced technique for anesthetic blockade - which targets a precise location or nerve - can derive from this knowledge and recognition of peripheral nerves located in the lower parts of limbs. To this date, nonetheless, there is no systematic evaluation of the nerves located in the lower regions of the upper and lower limbs by ultrasound.