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Peripheral Nerve Block

Updated on August 18, 2012

Peripheral nerve blocks are often used by anesthesiologists instead of, or in addition to, general anesthesia for surgery on the extremities (arms and legs).

As with all medical procedures, peripheral nerve blocks provide some benefits and some risks. This risk:benefit ratio must be considered when deciding if a peripheral nerve block is a good choice in each situation.

This is a very general overview of what your doctor means when they talk about peripheral nerve blocks.

Knowledge of anatomy is crucial for safe placement of peripheral nerve blocks, such as this interscalene nerve block.
Knowledge of anatomy is crucial for safe placement of peripheral nerve blocks, such as this interscalene nerve block. | Source

What is Peripheral Nerve Block?

Peripheral nerves are, quite generally, those nerves that are not part of the central nervous system, which is made up of the brain and spinal cord. Peripheral nerves provide sensation and movement to the rest of the body.

A peripheral nerve block, therefore, numbs a nerve or group of nerves to achieve anesthesia of the desired body part. Examples of commonly used peripheral nerve blocks are the femoral nerve block used for knee surgery and the interscalene block used for shoulder surgery.

How is a Peripheral Nerve Block Done?

A knowledge of anatomy is essential for placement of nerve blocks. A large nerve root leaves the spinal cord and branches out as it spreads over the body. Each of these branches may then join up with branches from other nerve roots to form the nerves that go on to innervate different parts of the body. Instead of numbing each individual end nerve, anesthesiologists placing peripheral nerve blocks often take advantage of knowing where the larger nerves are, before their branch points. For example, to numb the front of the thigh and knee, the nerve block is actually placed at the upper thigh before the femoral nerve divides into smaller branches.

Each type of nerve block is placed based on this knowledge of standard anatomy. There is, of course, some variability from patient to patient. But, much of the anatomy is fairly consistent in relation to anatomic landmarks.

The LANDMARKS are located near the site where the nerve can be expected to be found. These landmarks might include bony or vascular (blood vessel) structures. The site of injection is then located based on these landmarks.

NUMBING MEDICINE for the skin may or may not be used at the site of the injection depending on the sensitivity of the site.

Poor Audio and Spelling, but the Twitch from the Nerve Stimulator is well demonstrated for Femoral Nerve Block with Nerve Stimulator Technique

Ultrasound Picture for Placement of Femoral Nerve Peripheral Nerve Block

Injection of LOCAL ANESTHETIC will be done near the nerve. Several different techniques are used to find the best spot for injection, close to, but not too close to, the nerve.

  • Paresthesia - The paresthesia technique is the oldest of the three. This involves using a needle to slowly get closer to the nerve while questioning the patient about what they feel. A feeling of tingling or pins and needles indicates a good position. Severe pain indicates that the needle is too close to the nerve. This technique has been replaced by better, safer and more comfortable procedures.
  • Nerve Stimulator - With a nerve stimulator technique, the needle used is insulated and connected to a special monitor-stimulator that applies low dose electric current. When the nerve is approached, the nerve is stimulated and muscle movement indicates correct placement of the needle. Patients do not report this as being painful or even uncomfortable. They usually say it feels 'weird' that their muscle contracted on its own.
  • Ultrasound - Ultrasound is the newest method in use to locate the location of the nerve. This technique actually provides visualization of the nerve and surrounding structures using sound waves to produce highlights and shadows that show the anatomy.

Once the correct position is found with the needle by one of the above techniques, the medicine is injected slowly after confirming that the needle isn't in a blood vessel. Injection directly into the blood stream would lead to local anesthetic toxicity and potentially life-threatening complications.

What are the Benefits of a Peripheral Nerve Block?

Peripheral nerve blocks are more often used for post operative pain relief than they are for the surgical anesthesia.

  • They can significantly decrease the amount of narcotic pain medication needed for the first few hours to the first day after surgery.
  • General anesthesia can be reduced or avoided completely. This can be beneficial to patients who are high risk for general anesthesia or those who have significant side effects of general anesthesia.
  • Time spent in the recovery room can be decreased.

What are the Risks of a Peripheral Nerve Block?

Complication rates vary depending on the technique used to place a block and the location of the block (for example, interscalene blocks used for shoulder surgery have higher complication rates than femoral nerve blocks used for knee surgery).

  • Injury from the needle: Anytime a needle is used, infection, bleeding and nerve injury from the needle can occur
  • Local anesthesia: Local anesthesia toxicity can occur from an overdose of the injected medication if it is injected or absorbed into the bloodstream. Loss of consciousness, seizures and cardiac arrest are extreme and dreaded potential consequences of this complication.


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