A nerve block is an injection of numbing medication delivered directly next to a specific nerve or group of nerves, temporarily stopping pain signals from reaching your brain. The procedure typically takes 15 to 30 minutes and follows a consistent sequence: positioning, skin preparation, imaging to locate the nerve, and a carefully placed injection. Here’s what actually happens at each stage.
Before the Procedure
If your nerve block involves sedation, you’ll likely be asked to fast beforehand. The standard guidelines allow clear liquids (water, black coffee, juice without pulp) up to two hours before the procedure and a light meal up to six hours before. Heavier or fatty foods may require eight or more hours of fasting. Your care team will give you specific instructions based on whether you’re receiving sedation and what type of block is planned.
You’ll also go through a brief pre-procedure check: a review of your medical history, a quick physical exam, and confirmation that you’ve followed the fasting instructions. If you take blood thinners or other medications that could affect bleeding or clotting, those details will have been sorted out in advance.
Step-by-Step: What Happens During the Block
You’ll be positioned on an exam table in a way that gives your provider clear access to the injection site. The exact position depends on which nerve is being targeted. A block in the shoulder area means you’ll likely be seated or semi-reclined, while a block for leg surgery might have you lying on your back or side.
If sedation is part of the plan, you’ll receive it through an IV line in your arm. This keeps you relaxed but not fully asleep. Many nerve blocks are done with minimal or no sedation at all.
Next, the skin over the injection site is cleaned with an antiseptic solution. Before the main injection, you’ll get a small shot of local anesthetic to numb the skin itself, so the deeper needle insertion is more comfortable.
Your provider then uses imaging to find the exact target. In most cases, this means an ultrasound probe placed on your skin, which shows nerves, blood vessels, and surrounding tissue in real time on a monitor. The provider can watch the needle tip as it advances, adjusting the angle and depth to land precisely next to the nerve. Some procedures, particularly those involving the spine, use X-ray (fluoroscopy) or CT guidance instead. Ultrasound has the advantage of showing soft tissue clearly and tracking the needle in real time without any radiation exposure.
Once the needle is in position adjacent to the nerve, the medication is injected slowly, usually in small increments of about 5 mL at a time. Between each increment, the provider gently pulls back on the syringe to make sure the needle isn’t inside a blood vessel. A total volume of 20 to 50 mL is common, depending on the type of block. On the ultrasound screen, the provider can actually see the anesthetic spreading around the nerve.
Common Types of Nerve Blocks
The technique is adapted to different parts of the body depending on what surgery or pain condition is involved.
- Interscalene block: Targets nerves in the neck that supply the shoulder and upper arm. Used for shoulder surgeries and some upper arm procedures.
- Femoral nerve block: Targets the main nerve on the front of the thigh. Used for knee replacements, ACL repairs, and other surgeries on the front of the leg. The nerve is located next to the femoral artery using ultrasound, and the needle is guided to sit right beside it.
- Sciatic nerve block: Targets the large nerve running through the buttock and down the back of the leg. Used for foot and ankle surgeries. The nerve is found deep to the gluteal muscles, and the needle is inserted from the side or back of the hip.
Each block numbs a specific territory. Your provider chooses the type based on exactly where your pain or surgery is located.
How Quickly It Works and How Long It Lasts
You’ll start to feel numbness within about 13 to 17 minutes, depending on the medication used. Faster-acting agents like lidocaine kick in around the 13-minute mark, while longer-lasting agents like bupivacaine take closer to 17 minutes.
Duration varies significantly by medication choice. A lidocaine-based block provides roughly 3 hours of pain relief. Bupivacaine, the more common choice for surgical pain, lasts considerably longer, around 7 to 9 hours. Providers sometimes mix medications to balance a quicker onset with a longer duration, which typically produces 6 to 8 hours of relief. Some blocks also include additives that can extend the effect further.
Risks and Complications
Nerve blocks are considered safe, but complications do occur. In a study of 855 blocks performed for foot and ankle surgery, about 10% of patients experienced a short-term complication, and 4.3% had a longer-lasting issue. The vast majority of those complications, roughly 97%, were sensory problems like prolonged numbness or tingling rather than any loss of muscle function.
The most serious potential complication is local anesthetic systemic toxicity, which happens when too much numbing medication enters the bloodstream. This is rare but can affect the heart and nervous system. It’s the reason providers inject in small increments with aspiration checks in between, and why facilities that perform nerve blocks keep specific rescue protocols on hand.
Other possible risks include bleeding or bruising at the injection site, infection, and temporary nerve irritation that causes tingling or weakness lasting days to weeks.
What Recovery Looks Like
After the block, you’ll spend a short time being monitored before going home. The most important thing to understand is that your limb will be numb and possibly weak for several hours, and you need to treat it carefully during that window.
While the block is active, protect your numb limb from heat and cold, since you won’t be able to feel burns or frostbite. Keep the arm or leg supported and avoid placing it in awkward positions that could cause injury without you realizing. If your leg is blocked, don’t try to walk without assistance, as you could fall. Avoid operating machinery or doing anything that could hurt you while sensation is absent.
One practical tip that makes a real difference: take your prescribed pain medication before the block fully wears off, especially if that’s going to happen overnight. The transition from complete numbness to no nerve block at all can be abrupt, and having pain relief already working in your system prevents a painful gap. If numbness or weakness in your limb persists beyond 36 hours, contact your hospital’s anesthesia team for guidance.