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FEMORAL NERVE BLOCK

INTRODUCTION

Over the past 5 years, thousands of patients have experienced excellent pain relief following knee surgery with a nerve block. Using this technique, local anesthetic is placed around the femoral nerve, providing pain relief to the front and inner side of the knee. Patients undergoing a total knee replacement or knee ligament reconstruction will have the opportunity to discuss options for pain relief with an anesthesiologist prior to surgery.

ADVANTAGES

Studies show that patients with a nerve catheter require less of the narcotic-type pain medications such as oxycontin, which can make you feel nauseated or sleepy. The research also indicates that people who have a nerve catheter are better able to participate in physical therapy and may be discharged home from the hospital earlier compared with people who do not have a nerve block.

RISKS

These procedures are extremely safe. In one series of over 600 patients treated at a University Orthopedic Surgery center with nerve blocks, only two patients had nerve-related complications. Complications typically include prolonged loss of sensation and in some cases prolonged weakness in the distribution of the nerve block. Usually these effects go away within a few weeks, as we saw in our two patients. It is extremely rare to have a permanent nerve injury from one of these blocks. Additional risks include a failed block (meaning the local anesthetic has not had a negative effect, it just doesn't take the pain away) and an unintentional injection into a blood vessel. Placing local anesthetic into your blood stream can cause an uncomfortable feeling, ringing in your ears and metal taste in your mouth. Large quantities of local anesthetic can lead to loss of consciousness and significant suppression of heart function. This is very rare and especially unlikely given that doctors use ultrasound to see where the arteries and nerves are located.

BLOCK PLACEMENT

Before placing the nerve block, an IV will be started and an anti-anxiety medication will be offered. The anesthesiologist will monitor vital signs (heart rate, blood pressure, and blood oxygen level) and supplemental oxygen will be administered if needed. Recent advances in ULTRASOUND technology have led to the development of portable high resolution ultrasound machines that allow physicians to see nerves, blood vessels, and other key structures. We think that using ultrasound makes our nerve blocks safer and more effective.

To place a femoral nerve block, patients are laid down on their back. Their groin area is exposed on the same side as the knee to be replaced. The groin area will be washed off with a special antibacterial soap. Before positioning the needle, a small amount of local anesthetic is used to numb the skin. The nerve block feels similar to having an IV started. As the local anesthetic is injected, patients sometimes feel pressure in the area. Using ultrasound, the physician places the needle near the nerve, but avoids uncomfortable sensations associated with touching the nerve. Ultrasound also helps doctors prevent placing the needle into blood vessels. Once the needle is placed in the correct position, an ounce (or 20 to 30 milliliters) of local anesthetic is injected around the nerve. This dose of local anesthetic typically provides 8 to 12 hours of pain relief.

Once the local anesthetic is placed around the nerve, a catheter is placed through the needle and threaded 2 inches past the tip of the needle. The needle is then removed. The catheter is secured to your skin with sticky spray and a clear bandage. Patients often experience weakness and numbness over the front of the leg within 15 to 30 minutes of block placement

SURGICAL ANESTHESIA

The nerve block does not provide the sole anesthetic for the surgery. For a knee replacement, most people have a spinal anesthetic, but some, after careful consultation with their anesthesiologist, choose to go to sleep for surgery. The nerve block has no effect on how the surgery is performed or what type of anesthesia will be used.

PAIN CONTROL AFTER SURGERY

After surgery, the femoral nerve block provides pain control for the front of the knee. Although the incision is on the front of the knee, some patients feel pain in the back of their knee. The pain on the back of the new is usually easily treated with pain pills.

THE NERVE CATHETER

In the recovery room, an infusion pump is attached to the nerve block catheter and the pump is typically run for one and a half to two days. The nerve catheters can have small leaks at the skin, so a piece of gauze is placed under the clear plastic dressing to absorb local anesthetic that leaks out to the skin from the nerve catheter. After 2 days, to avoid infection risks, the nerve block catheters are removed. The most uncomfortable part of this is the removal of the clear plastic tape. Many patients are sent home with the nerve catheters and simply remove the catheter themselves once all of the medication has been infused.

CONCLUSION

We hope you have found this information helpful as you consider your pain management options for your upcoming knee surgery.

FAQ

What is a peripheral nerve block?

A peripheral nerve block is a blockage of pain signals from a nerve to the brain, creating a numb area. This is accomplished by surrounding the nerve with a local anesthetic. A commonly used local anesthetic is called bupivacaine.

How is a peripheral nerve block performed?

The anesthesiologist will identify the nerve using ultrasound, then clean off your skin with sterile solution. A small amount of local anesthetic is injected to numb the skin, and a needle is guided under ultrasound to a location near but not touching the nerve. The local anesthetic is then injected near the nerve.

How long will it take to get numb?

About 20 minutes.

How long will the nerve be numb?

It depends. If a single injection of local anesthetic is performed, you will be numb for 8-12 hours. If a nerve catheter is places, you will be numb for 2 days. For a total or partial knee replacement, a catheter is usually placed.

What is a nerve catheter?

A nerve catheter is a thin piece of flexible plastic tubing that is placed under the skin near the nerve. It is fastened to the skin with a bandage and connected to a plastic pump about the size of a baby bottle. The pump will inject local anesthetic for about two days.

How do I take care of a nerve catheter?

Just don’t pull the bandage off! When it’s time to remove the nerve catheter (you’ll know it’s time because the balloon inside the bottle will be empty), remove the bandage and the catheter. If the catheter doesn’t come out easily, come back to the hospital and we will remove it for you.

What are the side effects of a peripheral nerve block?

Your leg will be numb and weak. If you’re able to walk on your operative leg after surgery, you must be very careful to do so with help while the nerve block is in place. Please be aware of where your leg is at all times, as your leg could be injured without your knowledge (by stubbing your toe, for example).

What are the risks associated with a peripheral nerve block?

The three major risks of a nerve block are infection, bleeding, and nerve damage. These are all extremely rare complications. However, if you already have numbness or tingling in your leg or foot, please let the anesthesiologist know. A nerve block may be more likely to cause nerve damage if you already have these symptoms.

A peripheral nerve block will not provide all of the pain relief needed in the first two days after your surgery, and sometimes the peripheral nerve block doesn’t work at all and has to be redone.

What are the benefits associated with a peripheral nerve block?

A peripheral nerve block provides superior pain relief to oral or intravenous pain medicines alone. We find that adding a peripheral nerve block to the oral or intravenous pain medicines allows people to participate in physical therapy better and that they need less of the morphine-type pain medicines. Since the morphine-type pain medicines can make you groggy, nauseated, constipated, and itchy, we think needing less of them is better.

Do I still need to go to sleep for my surgery?

The peripheral nerve blocks does not provide enough pain relief to have surgery. You will need to either go to sleep (general anesthesia) or to have a spinal anesthetic, which will make you numb for about three hours from the chest to your feet.

CONTACT

Contact pain_fellow@abl.med.utah.edu if you have additional questions or concerns.
Topic revision: 23 Jul 2008, NoahSyroid
 

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