A peripheral nerve block (PNB) is the injection of a local anesthetic near a specific nerve or bundle of nerves. This targeted injection temporarily interrupts the electrical signals traveling along that nerve pathway to the brain, providing localized pain relief and numbness to a specific part of the body, such as a limb or surgical site. This technique offers an effective alternative to general anesthesia for certain procedures and manages pain without the systemic side effects of oral medication.
How Peripheral Nerve Blocks Work
Nerves transmit sensations, including pain, through electrical impulses known as action potentials. These impulses are generated when voltage-gated sodium channels, specialized pores in the nerve cell membrane, open to allow a rapid influx of positively charged sodium ions, creating the electrical signal.
The local anesthetic medication, such as lidocaine or bupivacaine, is injected near the nerve bundle where it diffuses into the nerve tissue. Once inside the nerve cell, the anesthetic molecule binds to and blocks the voltage-gated sodium channels. This blockade prevents the necessary sodium influx, effectively halting the generation and conduction of the electrical impulse. When the pain signal cannot travel past the injection site, the brain never receives the message, and the area becomes numb. The duration of the block is related to the specific anesthetic drug used and the time it remains concentrated around the nerve tissue.
When Are Nerve Blocks Used
Peripheral nerve blocks are widely employed in acute care settings to manage pain associated with surgery and trauma. They can be used as a standalone anesthetic for operations on the extremities, such as hand or foot surgery, allowing the patient to remain awake. For more complex operations, a PNB may be utilized alongside general anesthesia to enhance pain control during and immediately following the procedure.
A primary application is post-operative pain management, where a block provides hours or even days of targeted relief to the surgical site. This focused approach reduces the need for systemic opioid medications, which can cause side effects like nausea and respiratory depression. Nerve blocks are also commonly used in emergency departments to provide rapid pain relief for fractures, joint dislocations, or other acute injuries before a definitive procedure takes place. PNBs can also be used to diagnose and treat certain types of chronic pain, like sciatica or complex regional pain syndrome.
The Procedure and Variations
Administering a peripheral nerve block requires precise placement of the needle tip and the anesthetic agent adjacent to the target nerve bundle. To ensure accuracy, providers often use advanced guidance techniques, most commonly ultrasound imaging, which allows the clinician to visualize the nerves, surrounding anatomy, and the real-time spread of the injected medication.
Another method involves using a peripheral nerve stimulator, which delivers a small electrical current through the needle tip to elicit a specific muscle twitch when the needle is close to the nerve. Precise localization is paramount to maximize the block’s effectiveness while minimizing the volume of anesthetic required.
The two main variations are the single-injection block and the continuous nerve block. The single-injection technique provides a finite duration of pain relief, typically lasting up to 24 hours depending on the drug chosen.
The continuous nerve block involves placing a small, flexible catheter next to the nerve after the initial injection. This catheter is connected to a portable pump that continuously or intermittently delivers a low dose of local anesthetic over several days. This method is especially beneficial for surgeries associated with high levels of post-operative pain, such as major joint replacements, providing extended pain relief.
What to Expect After the Block
Following the procedure, the onset of numbness and muscle weakness in the blocked area typically occurs within minutes to an hour, depending on the specific nerve and medication used. The duration of the profound block can range from six to 36 hours before the anesthetic begins to dissipate, causing a gradual return of sensation. As the medication wears off, patients frequently experience tingling, pins and needles, or a feeling of heaviness as the nerve function returns.
The most important aspect of post-block care is protecting the numb limb from unintentional injury since the lack of sensation means the patient cannot feel heat, cold, or excessive pressure. Healthcare providers will instruct patients to take their prescribed oral pain medication before the block fully wears off to prevent a sudden onset of severe pain.
While rare, patients should seek immediate medical attention if they experience severe pain not relieved by medication, signs of infection like redness or warmth at the injection site, or persistent numbness or weakness lasting longer than 48 hours. The gradual return of motor function and sensation is the expected process, but any electric shock-like sensations or concerning changes should be reported.