Overview of Femoral Nerve Block
Peripheral nerve blocks are a way of stopping pain signals from reaching the brain. This is done by using a local anesthetic to pause the activity in the affected nerve endings. It’s a bit like turning off a loudspeaker; the sound doesn’t disappear, it just can’t be heard anymore.
The type of anesthetic used, how strong it is, and how much is used can all influence how quickly it works, how long it lasts, the level of numbness, and how much it spreads to other nerves.
A particular type of this treatment is called a femoral nerve block. It’s designed to numb the area around the femoral nerve, which is found in the front of the thigh and knee. Surgeons often use this nerve block during operations involving these parts of the body.
This method can actually provide effective pain relief while reducing the need for opioids. Opioids are strong painkillers, but they can also cause many unwanted side effects. So, by using a femoral nerve block, patients can experience less pain and fewer side effects, which can, in turn, speed up their hospital discharge.
Anatomy and Physiology of Femoral Nerve Block
The femoral nerve is a major nerve that originates from the lower spine, specifically from the L2, L3, and L4 spinal nerves. It travels into the area known as the femoral triangle, which is situated below the hip’s fold. This nerve is the most outer part of this triangle, which also contains important blood vessels – the femoral artery and vein.
This nerve splits into two parts: the front and back. The front part provides feeling and movement to the inner part of the thigh and the sartorius muscle, which aids in knee and hip movement. The back part of the femoral nerve, known as the saphenous nerve, gives feeling and movement to the quadriceps muscle, which is the large muscle group at the front of your thighs.
In addition to providing movement, the femoral nerve is responsible for sensation in the front of the thigh and knee, as well as the inner part of the lower leg and foot below the knee. The saphenous nerve can be blocked for pain relief at multiple points along its path, including at the adductor canal, which is a passageway in the middle of your thigh. This canal starts from the femoral triangle and extends to the large inner thigh muscle known as the adductor magnus.
It’s important to note that because of the close connection of these structures, procedures that involve the adductor canal might potentially impact the femoral nerve’s functionality.
Why do People Need Femoral Nerve Block
A femoral nerve block (FNB) is a technique used by doctors to numb the front part of your thigh before conducting surgery. This method can also be combined with another procedure called a sciatic nerve block, which numbs the lower part of the leg below the knee. Sometimes, it’s also mixed with an obturator block, a procedure to numb the entire lower leg, for complete anesthesia in the lower extremity. You may receive a single injection or continuous infusions to help manage the pain after a total knee replacement surgery.
The femoral nerve block is not only effective for surgeries but also for relieving pain resulting from certain injuries such as fractures in the femoral neck, femur (the thigh bone), and patella (kneecap). This technique could be used on its own, or as a part of a pain management plan that involves several different strategies.
When a Person Should Avoid Femoral Nerve Block
There are a few reasons why a patient may not be able to receive a procedure that involves anesthetic or numbing medication. Firstly, if the patient has said ‘no’ to the procedure, can’t cooperate, or is highly allergic to the anesthetic medicine, the procedure can’t be performed.
Other less clear-cut situations could also affect whether the procedure can be done. For example, if a patient currently has an infection at the area where the anesthetic would be injected, or if a patient is taking certain medications that affect blood clotting, it may not be safe. Also, patients with problems related to bleeding may not be suitable for this procedure.
Lastly, the doctor needs to discuss the possibility of experiencing more damage to the nerves with patients who already have nerve damage or are at risk of nerve damage due to conditions like severe diabetes or prior nerve injury.
Equipment used for Femoral Nerve Block
Having the right tools is crucial when doing a femoral nerve block, which is a procedure used to numb the thigh area. To ensure cleanliness and prevent infections, the health professional should use an antiseptic solution, like chlorhexidine scrub. Wearing sterile gloves, a face mask, and a hospital cap is also very important. The doctor will also use a specific needle (20- or 22-gauge, 50- to 100-mm, short-bevel, insulated) which may have special features to assist in precise placement. They’ll also use a type of numbing medicine called lidocaine 1% using a 25 gauge needle to numb the area where they are inserting the main needle.
They’ll also need a bigger needle (20 mL) for the main numbing agent. This is all part of what’s known as a standard nerve block kit. If your doctor decides to use ultrasound guidance to help locate the nerve, they will need a special machine with an attachment called a linear transducer, a cover to keep the ultrasound probe sterile, a different insulated needle, and a special gel that helps the ultrasound work properly.
For the main numbing agent, there are a few options. They might use a long-lasting type of numbing medication like bupivacaine 0.5%, levobupivacaine 0.5%, or ropivacaine 0.5%, or a medium-lasting one like mepivacaine 0.5% or lidocaine 0.5%. These types of drugs should always be preservative-free for safety when used for nerve blocks.
Who is needed to perform Femoral Nerve Block?
The nerve block, which is a type of treatment to help control pain, should be carried out by a medical professional who is skilled in regional anesthesia. Regional anesthesia is a type of pain relief that affects a large area of the body. It might also require another person to help with injecting the local anesthetic, a drug that causes loss of sensation in a small part of the body. Having a nurse who knows about or has experience with regional anesthesia is definitely a plus.
Preparing for Femoral Nerve Block
Before beginning the procedure, the doctor will explain everything to you and make sure you agree to the treatment in line with the hospital rules. The doctor will also check and document any existing issues related to your movements and sensation capabilities.
For ensuring safety during the procedure, the doctor will monitor your pulse, heart activities, and blood pressure regularly (every 3 to 5 minutes) using various devices as per the American Society of Anesthesiology (ASA) guidelines. You will be given fluids through an IV (intervenous – a method of injecting directly into your veins) and will confirm it’s working properly. The doctor will also ensure that oxygen, equipment for sudden emergencies, and necessary medications are readily available. In case of any reaction to the local anesthesia, a specific treatment known as 20% lipid emulsion will be easily reachable.
Before the procedure starts, they will help you get into the right position. You will be laying flat on your back with the correct leg – the one they’re working on – straightened and slightly moved away from your body and rotated outwards.
The doctors may need to move excess skin or fat (called the pannus) in the groin area for better visibility during the procedure.
Lastly, before the procedure begins, a final safety practice called a “Time Out” is performed. This is a final chance to confirm everything before starting the procedure. Mild sedation can also be given if needed, depending on the hospital rules.
How is Femoral Nerve Block performed
There are two main methods of finding and treating the femoral nerve, which is located near the femoral artery and vein in the groin area.
Using Ultrasound Technology:
The technician uses an ultrasound machine to get a better look at your groin area. They place a device called a transducer on the skin, which uses sound waves to create an image of the internal structures. If more than one artery is visible, they will adjust the transducer’s position until only the common femoral artery (the main one) is seen along with the femoral vein. The femoral nerve is usually seen as a bright wedge or oval shape on the ultrasound screen. It is located between the large muscles of the hip and the surface tissue layers.
Once the femoral nerve and the surrounding structures are identified, the doctor will inject a dose of lidocaine (a local anesthetic) into the tissue to numb the area. The doctor then inserts a needle towards the femoral nerve, using the ultrasound image as a guide. They can approach the nerve from different angles depending on what works best for the situation. The doctor will make sure they aren’t puncturing a blood vessel by drawing back the syringe slightly to check for any blood. The needle delivers medication around the nerve, which the doctor can monitor in real-time using the ultrasound.
If the doctor meets resistance while injecting or notices the nerve is swelling, this might mean the needle has accidentally entered the nerve and they’ll need to adjust.
Using Landmark and Nerve-Stimulation Techniques:
Another technique involves finding the nerve manually, using anatomical landmarks and touch. First, the doctor locates the inguinal ligament (a band of connective tissue in the groin area) by feeling for two specific points on your hip and groin. They then find the femoral artery, which is usually located just below the crease of the groin. The needle is inserted about 1 cm to the side of the artery and directed upwards. The estimated depth for the femoral nerve is 2 to 4 cm below the skin surface, but this can vary depending on your body structure.
In this method, the doctor may also use a nerve stimulator. This device sends small electrical currents into the needle. When the needle gets close to the femoral nerve, this current makes your leg twitch. This twitching lets the doctor know they’re near the nerve. The doctor then gradually decreases the electrical current. If your leg stops twitching when the current is between 0.3 to 0.5 mA, then the needle tip is likely close enough to the nerve without poking into it. The doctor will then deliver the medication after confirming that they’re not in a blood vessel.
Remember, these techniques could be used separately or in combination, depending on your specific situation and what your doctor thinks is best.
Possible Complications of Femoral Nerve Block
Whenever a peripheral nerve block is performed, there are certain risks that patients should be aware of. A peripheral nerve block is a type of anesthetic that numbs a specific area, preventing pain during medical procedures. Potential issues can include damage to the nerves, allergic reactions, blood build-up in the area (known as a hematoma), infections, and a condition called local anesthetic systemic toxicity which is when too much of the anesthetic gets into your blood. Also, despite the doctors’ best efforts, there’s a slight chance that the nerve block might not work as planned. In such cases, other pain relief options should be available.
Temporary or permanent nerve damage could happen because of the needle accidentally poking a nerve or the anesthetic being injected directly into the nerve. Because of these potential risks, doctors make sure they have emergency resuscitation equipment close by, just in case the patient shows signs of local anesthetic systemic toxicity.
For situations where local anesthetic toxicity occurs, administering a 20% lipid emulsion (a special fat-based solution) can be effective. The dosage is calculated based on the patient’s lean body mass – with an initial dose of 1.5 mL/kg given over 1 minute. This is then followed by an ongoing infusion of 0.25 mL/kg/min until the patient’s heart rate and blood pressure stabilize. If the initial dosage doesn’t seem to work, doctors may consider giving another dose and increasing the infusion rate. However, it’s important to note that the 10% lipid emulsion found in a medication called propofol is not a suitable replacement for lipid emulsion therapy.
What Else Should I Know About Femoral Nerve Block?
The femoral nerve block is a type of treatment that affects both your motor nerves (which control muscle movements) and sensory nerves (which help you feel things). One of the side effects of this treatment is that it can make your quadriceps muscle – the large muscle at the front of your thigh – weaker. This can make moving around more difficult.
However, it’s possible to lessen this muscle weakness by using a lower concentration of the local anesthetics used in the treatment. It’s crucial to note that after receiving a femoral nerve block, you shouldn’t try to walk without help, as the muscle weakness could make you more likely to fall.
