Daniel B. Maalouf, MD, MPH
Assistant Attending Anesthesiologist, Hospital for Special Surgery
Clinical Instructor in Anesthesiology, Weill Medical College of Cornell University
A safe and successful practice of regional anesthesia relies on anesthetizing nerves that carry sensations from the surgical site without damaging their structure. A local anesthetic, such as mepivacaine or bupivacaine, is injected around the desired nerves using a nerve block needle. Disruption of the nerve structure with the needle can cause undesirable neurological consequences and must be avoided. Anesthesiologists trained in regional anesthesia achieve this goal by relying on anatomical landmarks, the patient’s own feedback, and the use of nerve stimulators to locate the targeted nerves. A nerve stimulator is a device that discharges a small electrical current that is delivered through a needle. When the needle tip approaches the nerve, the electrical current causes a twitch of the muscle that is supplied by that nerve, providing information to the anesthesiologist. Using this technique, the anesthesiologist can target specific nerves and deliver a dose of local anesthetic to anesthetize the surgical site. Nerve stimulation has been used to locate nerves for many years and is currently the most common technique. However, there are also drawbacks to this technique, one of which is the inability to directly visualize the path of the needle as it passes through tissue.
In the last decade, a new technique has emerged: the ultrasound-guided peripheral nerve block. The use of ultrasonography in the field of regional anesthesia helps visualize the targeted nerves, the needle as it moves through tissues, any vital structures in the vicinity, and adequate spread of the local anesthetics around the nerves. As previously mentioned, accurate delivery of local anesthetics around nerve structures ensures the right amount of anesthesia. Technological improvements and lower costs have made it possible for the anesthesiologist to utilize this technique in his/her practice of regional anesthesia.
The concept of ultrasound imaging relies on the ability of human tissue to reflect sound waves. Sound waves are emitted from the ultrasound probe into the tissue over which it is applied. These sound waves are then reflected back towards the probe as they cross different areas of the body. The probe receives the reflected waves and an image is created on the screen of the ultrasound machine. When using this technique, the anesthesiologist can visualize, in real time, the structures that he/she is looking for, pass the needle toward the targeted nerves, and avoid any vital structures on the way. This ensures success of the block by confirming an adequate spread of the local anesthetic solution around the nerve.
Because this technique is relatively new, many anesthesiologists are not familiar with it. However, the majority of our anesthesiologists at Hospital for Special Surgery do perform ultrasound-guided nerve blocks. Many of our staff members are also involved in clinical research to establish the safety and success of this technique. Some of our surgeons also participate in our research, and they recommend this technique to their patients.