Anesthesiologists experienced in regional anesthesia can precisely place peripheral nerve blocks (PNB) almost every time using their tactile sense and blind targeting techniques. But for mainstream anesthesiologists, this approach can be challenging to master, and the potential risk of intraneural or intravascular injection is a major concern.
The good news is that help is on the way, in the form of ultrasound imaging. High-frequency ultrasound imaging allows the anesthesiologist to see both the nerve and needle, and thus advance the needle safely and position the tip accurately. In my experience, ultrasound imaging can also help avoid incomplete or delayed blocks because the anesthesiologist can visualize the local anesthetic spread. I routinely reposition the needle tip during injection to ensure that enough anesthetic envelopes the nerve, and this helps ensure a complete block.
Fulfilling the promise
Right now, however, the promise of ultrasound imaging for regional anesthesia is still just that: A promise. The current body of research suggests that ultrasound techniques are at least as effective or more effective than traditional techniques, but there are no clear clinical safety data. Unfortunately, such outcomes research will require several thousand patients or more. Other barriers also exist, and one of the biggest is cost. The high-frequency ultrasonographic equipment and associated software that we need to visualize nerve structures costs $50,000 or more. In addition, we are still working to develop needles that are easy to see yet do not produce too much artifact. Anesthesiologists must also undergo specialized hands-on training to learn nerve-imaging and ultrasound-guided needling techniques.
Still, I believe there is a future for ultrasound imaging for regional anesthesia. Ultrasound technology typically takes a quantum leap every five years, and it won't be long before we will be able to use hand-held, high-resolution devices to image anatomy under normal room lighting conditions. As technology advances, costs will also come down, and new medical uses for high-frequency ultrasound will further justify the investment. For example, one new study recommends ultrasound-guided epidural anesthesia for neonates and infants, and another suggests advantages to using ultrasound imaging for evaluating lung status in the ICU. I liken this to the fiberoptic bronchoscope that we now use for difficult intubations. Years ago, this seemed rather esoteric; now, it plays a practical clinical role.
Imaging a key driver
Perhaps most importantly, my experience suggests that ultrasound-guided imaging helps residents and other anesthesiologists overcome their fear of performing PNBs. When I look into the future, I see ultrasound imaging as a key driver in our quest to move regional anesthesia fully into the mainstream, which is exactly where it belongs.
Dr. Chan is a professor with the Department of Anesthesia and Pain Management, University of Toronto, and is on staff at the Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada.