By Christopher W. Hackney, M.D.
“Is this something new?” This is the most common question I am asked when discussing peripheral nerve blocks with patients.
While various regional techniques have been employed for over a century, the widespread use of peripheral nerve blocks have become a relatively recent phenomenon in the field of anesthesia. At the end of the 19th century, cocaine started to show promise as a powerful anesthetic for medical procedures. Cocaine’s inception opened the doorway as a potent surgical anesthetic, however that doorway also lead to addiction and dependency for many practitioners.
Throughout the next century, newer advents of local anesthetic provided a resurgence. So while cocaine’s abuse potential limited its utilization, newer local anesthetics combined with peripheral nerve blocks have become to be powerful tools in minimizing opioid usage and subsequent long- term abuse potential.
In its first decades of use, cocaine not only proved to be habit forming but also carried with it the risk of cardiac toxicity. Innovations into less cardiotoxic formulations, such as procaine and lidocaine, helped pave the way for our current generation of local anesthetics. Bupivaicaine and Ropivaicaine are now the most commonly utilizedused anesthetics for peripheral nerve blocks.
While the former has a greater potential for cardiotoxicity in the event of an overdose, theythese are still vastly superior in improving block duration than previous generations. Combined with peripheral nerve blocks, modern local anesthetics can provide 12 to 24 hours of pain relief.
Peripheral nerve blocks involve the targeted administration of local anesthetic in order to functionally “block” stimulation from a specific area of the body during a surgical procedure. Visualization with an ultrasound machine aides in localization of nerves and the guidance of a needle through which to local anesthetic is administered.
Due to variations in diameter and myelination, local anesthetics affect nerve fibers differently, but the main targets for anesthetization are the type C fiber nociceptors and type A delta fibers. Interrupting the conduction of a pain stimulus from a surgical area can diminish and in many situations eliminate surgical pain.
Because local anesthetics do not discriminate the nerve fibers they affect, other consequences of a peripheral nerve block include loss of touch, proprioception, and temperature discrimination, as well as motor strength to the area.
Orthopedic surgery has historically been the most well- served utilizingusing regional anesthesia. A peripheral nerve block along the cords of the brachial plexus can effectively anesthetize the forearm and hand for surgery. The shoulder itself can also be blocked by an injection at the level of the roots of the brachial plexus.
The lower extremity is susceptible to peripheral nerve blocks in a similar manner. Both the femoral and sciatic nerve are easily isolated to benefit any number of procedures involving the leg and foot.
Visualization of peripheral nerves directed by ultrasound allows for more precise administration of local anesthetics. In addition, ultrasound also allows to better visualization ofe nerves and the spread of local anesthetic during the procedure. Ultrasound has allowed for much safer placement of peripheral nerve blocks as well improvement in onset and duration genericoitalia.it.
Peripheral nerve blocks for orthopedic procedures are not only important for reducing perioperative pain, but also in necessitating early physical therapy in many procedures such as total knee arthroplasties. For these procedures, a variant of the femoral nerve block, the adductor canal block, is employed and serves to anesthetize the femoral nerve distal to the motor fibers innervating the quadriceps.
This technique allows for postoperative pain relief at the surgical site and avoids undesired motor weakness of the quadricep. Both promote early mobility and enhanced range of motion after total knee arthroplasty.
Although direct ultrasound visualization of the nerves with ultrasound is the approach to many blocks, newer techniques have focused on the development of fascial plane blocks. Specifically, the transversus abdominis plane (TAP) block and the pectoralispectoral nerves (PEC) block are allowing anesthesiologists to provide areas where traditional nerve anatomy is more diffuse.
Again uUnder ultrasound guidance, the TAP involves spreading a large volume of local anesthetic between the inner oblique muscle and the transversus abdominis muscle to provide anesthetization to the anterolateral abdominal wall, including the deep muscle and fascia. The TAP block has seen most success in proving to reduce post-operative opioid consumption for a variety of abdominal procedures both open and laparoscopic.
More recently, the pectoralisPEC block is giving anesthesiologists a better way to provide anesthetization to the anterior chest wall and axilla during a variety of breast procedures. These patients have an exceptionally high incidence of postoperative nausea and vomiting (PONV), which can be improved by reducing opioids through the placement of a PEC block.
However, the pectoralisPEC block and other fascial plane blocks are limited in their ability to produce a definitive block. Because their efficacy relies on the distribution of local anesthetic through a fascial plane, the outcome can be highly variable depending on a patient’s anatomy. For larger resections involving the anterior chest wall, such as partial and total mastectomies, a paravertebral block is more commonly employed. A paravertebral block is performed more proximally along the transverse processes of the spine to target the dorsal and ventral rami at a specific vertebral level. In doing so, a more complete band of anesthesia can be provided to one or more dermatomes along the chest wall.
These blocks represent only a fraction of an anesthesiologist’s arsenal in combating perioperative pain. Still, peripheral nerve blocks serve as only one part of an anesthetic plan, as they are usually combined with a general anesthetic to better optimize patient comfort. And while opioids may not be entirely eliminated from many patient’s’ anesthetic regimens, they are greatly diminished for those patients undergoing a procedure with a peripheral nerve block in place.
Among the anesthesia community, there has always been concern over the perioperative use of opioid pain medication. Opioids carry a range of side effects, from the rather innocuous post-operative itching to life-threatening respiratory depression. However, the current opioid epidemic has placed a greater precedence on reducing opioid use inin an attempt to trying to prevent future abuse by patients.
Peripheral nerve blocks have been proven safe and effective in the vast majority of procedures, including outpatient surgery. In addition, there are fewer complications associated with peripheral nerve blocks than traditional neuroaxial anesthesia, including spinal and epidural injections.
These procedures have their place in helping minimizing opioid consumption as well but place patients at a higher risk of hypotension and potential bleeding. Peripheral nerve blocks also lend to the advent of newer block techniques, which are helping facilitate greater implementation of regional anesthesia in all surgeries.
Many physicians are also looking at the potential for block additives, including dexamethasone, tramadol, dexmedetomidine, and clonidine to enhance the effect of a peripheral nerve block or extend its duration. Peripheral nerve catheters are also becoming more effectively used to extend block duration past the traditional 24 hours of a traditional single injection.
So while the use of local anesthetic with peripheral nerve blocks promises improved pain relief for patients in the postoperative period, anesthesiologists are also able to provide a much needed alternative to opioid pain medications.