A nerve block is an injection of local anesthetic around a specific nerve or bundle of nerves to completely numb a region of your body during and after surgery. It works by stopping pain signals from traveling from the surgical site to your brain, and it can provide relief lasting anywhere from 24 to 72 hours. Nerve blocks are used either as the primary form of anesthesia for a procedure or alongside general anesthesia to reduce pain during recovery.
How a Nerve Block Stops Pain
Nerves transmit pain signals as electrical impulses, and those impulses depend on sodium ions flowing through tiny channels in nerve cell membranes. The anesthetic drug physically occupies these sodium channels, preventing ions from passing through. Without that flow, the nerve can’t fire, and the pain signal never reaches your brain. The effect is localized: only the nerves bathed in the anesthetic are affected, so the rest of your body functions normally.
This is different from general anesthesia, which renders you unconscious. With a nerve block, you can be fully awake or lightly sedated while an entire arm or leg remains completely numb. That targeted approach means less exposure to the systemic drugs used in general anesthesia, which often translates to less nausea, less grogginess, and a faster recovery after surgery.
Common Types and Where They’re Used
The specific block you receive depends on where your surgery is. Each one targets a different set of nerves:
- Interscalene block: Numbs the shoulder, upper arm, and sometimes the hand by targeting nerve roots in the neck (the brachial plexus). Used for shoulder surgeries and some upper arm procedures.
- Supraclavicular block: Targets the brachial plexus just above the collarbone, providing numbness from the upper arm down to the hand. Common for elbow, forearm, and hand surgeries.
- Femoral nerve block: Numbs the front of the thigh and knee. Frequently used for knee replacements and ACL repairs.
- Sciatic nerve block: Numbs the back of the thigh, lower leg, and foot. Often paired with a femoral block for more complete lower leg coverage.
These are all peripheral nerve blocks, meaning they target nerves outside the spinal cord. Epidurals and spinal blocks, which deliver anesthetic near the spinal cord itself, are a separate category most commonly associated with childbirth and abdominal surgeries.
What Happens During the Procedure
Most nerve blocks today are performed using ultrasound guidance. Your anesthesiologist places a small ultrasound probe on your skin to generate a live image of the nerves, surrounding muscles, blood vessels, and bone. This lets them see exactly where the needle tip is in relation to the target nerve, which improves accuracy and reduces the chance of complications.
The needle is advanced toward the nerve under real-time imaging. Once the tip is in the correct position, the anesthetic is injected and can often be seen spreading around the nerve on the ultrasound screen. The injection itself takes only a few minutes. You may feel pressure or a brief sting at the skin, but the area is usually numbed with a small amount of local anesthetic first. Most patients describe the process as far less uncomfortable than they expected.
Sedation is typically offered during placement, so you may feel relaxed or drowsy. The block begins working within 10 to 30 minutes, and your surgical team will confirm that the area is fully numb before proceeding.
Single Injection vs. Continuous Catheter
A single-injection block delivers one dose of anesthetic and provides pain relief that gradually fades as the drug is metabolized. For many outpatient procedures, this is sufficient.
For more extensive surgeries or procedures known to cause significant postoperative pain, your anesthesiologist may place a thin, flexible catheter near the nerve instead. This catheter connects to a small portable pump that continuously delivers anesthetic, extending pain relief for two to three days. You can go home with the pump in a small carrying case, and the catheter is removed easily when it’s no longer needed. Continuous catheters are especially common after major joint replacements and complex orthopedic repairs, where pain management in the first few days is critical for starting physical therapy.
What It Feels Like as It Wears Off
Expect the blocked area to remain numb for at least 24 hours after a single injection. Depending on the anesthetic used and the dose, numbness can persist for up to 72 hours. The two most commonly used long-acting anesthetics produce slightly different timelines: one tends to provide sensory numbness averaging around five and a half hours in clinical settings, while the other extends that closer to six hours, though real-world surgical doses at higher concentrations and volumes often push total numbness well beyond those figures.
As the block wears off, sensation returns gradually. You’ll likely notice tingling or a “pins and needles” feeling first, followed by a dull awareness of the surgical site, and eventually full sensation. Motor function (the ability to move the limb) typically returns before the pain-blocking effect fully fades, though this varies. Up to 15% of patients notice lingering tingling or altered sensation in the days immediately after surgery. This is common and almost always resolves on its own.
Because the transition from numb to painful can happen relatively quickly, your surgical team will usually give you oral pain medications to start taking before the block wears off completely. Staying ahead of the pain rather than waiting until the block is gone makes a significant difference in comfort.
Risks and Complications
Nerve blocks have a strong safety record, but no procedure is risk-free. The most closely watched complication is local anesthetic systemic toxicity, which occurs when too much anesthetic enters the bloodstream. This happens in roughly 0.27 out of every 1,000 blocks. Early warning signs include tingling around the mouth, ringing in the ears, a metallic taste, confusion, or agitation. In rare cases it can progress to seizures or heart rhythm problems. Anesthesia teams are trained to recognize and treat this immediately, and a specific antidote is kept on hand wherever nerve blocks are performed.
Nerve injury is the other concern patients ask about most. Temporary symptoms like numbness or tingling beyond the expected duration occur in 0 to 2.2% of patients at three months. By six months, that drops to under 1%. Permanent nerve injury is rare, estimated between 0.014% and 0.04% of cases. Ultrasound guidance has helped reduce these numbers by allowing providers to see the needle’s position relative to the nerve in real time.
Other possible complications include bruising or soreness at the injection site, infection (uncommon with sterile technique), and, for blocks performed near the chest, a small risk of puncturing the lining of the lung.
Who May Not Be a Good Candidate
Certain conditions increase the risk of a nerve block enough that your anesthesiologist may recommend an alternative. Active infection at or near the injection site is an absolute reason to avoid the procedure, since introducing a needle through infected tissue could spread bacteria deeper.
Blood-thinning medications and bleeding disorders require careful evaluation. Blocks placed near deep structures where bleeding would be hard to detect or control are considered high risk in patients on blood thinners. For patients with low platelet counts, a level above 75,000 per microliter is generally considered adequate when no other risk factors are present, though the decision is always individualized.
Patients with pre-existing nerve damage in the area being blocked also need special consideration. A nerve that’s already compromised may be more vulnerable to the temporary effects of local anesthetic, and it can be harder to distinguish new symptoms from old ones after surgery. This doesn’t necessarily rule out a block, but it changes the risk-benefit conversation.