Fundamentals of regional anesthesia

1

What are the indications and contraindications for regional anesthesia?

Peripheral nerve blocks can provide surgical anesthesia and/or intra- and postoperative analgesia for upper and lower limb, thoracic, abdominal, breast, and head and neck surgeries. Common surgeries performed with nerve blocks include various orthopedic procedures, amputations, thoracotomies, laparotomies, arteriovenous fistula creations/revisions, and mastectomies. Contraindications for peripheral nerve block include patient refusal, sepsis/bacteremia, infection at injection site, preexisting neuropathy, and coagulopathy.

2

Name the advantages and disadvantages of peripheral nerve blockade versus general anesthesia when used as the primary anesthetic technique?

Regional techniques are especially helpful in cases for which general anesthesia is undesirable; for example, patients with anticipated difficult airway or severe cardiopulmonary disease could avoid pulmonary complications or hemodynamic instability by undergoing procedures under regional block. In addition, the opioid-sparing effects of nerve blocks are particularly useful for perioperative pain control in patients with obstructive sleep apnea, severe postoperative nausea and vomiting, chronic opioid therapy, opioid abuse history, or allergies to analgesics. Local anesthetic injection also causes vasodilation at the block site, which can aid in perfusion of flaps or extremities with compromised perfusion.

Procedures performed under regional block require patient cooperation, so this technique may be unsuitable for children or patients with high anxiety, developmental delay, altered mental status, or dementia. Patients may report inadequate sensory loss just before surgical incision, which can be because of either incomplete nerve block or insufficient time between block and incision. Another disadvantage of performing procedures under regional anesthesia is that preoperative blocks may prove inflexible if intraoperative findings change the surgeon’s approach to include areas not covered by the block. For these reasons, regional blocks are often performed in conjunction with general anesthesia, instead of being the primary anesthetic technique.

3

What are the different methods for providing regional anesthesia?

Peripheral nerve blocks can be performed as a single injection or as a continuous infusion via indwelling catheter. Similarly, neuraxial blockade may be performed as an injection into the subarachnoid space (spinal anesthesia) or as a continuous infusion into the epidural space. Another method of delivery is IV regional anesthesia (also known as Bier block ), in which local anesthetic is injected intravenously into an extremity in the presence of an inflated tourniquet.

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Describe the technique for performing a Bier block.

To perform a Bier block, an IV is placed in the operative extremity. After elevating the extremity and exsanguinating the limb (through the application of a compression bandage), a double tourniquet is inflated, and lidocaine (≤ 3 mg/kg) is injected into the operative extremity, IV. The extremity is then lowered, the IV removed, and the surgical procedure can proceed, while the patient breathes spontaneously with or without sedation. This type of block is typically used for procedures lasting 30 to 45 minutes, as longer procedures are generally limited by tourniquet pain.

5

What different techniques are used for performing peripheral nerve blocks?

Most peripheral nerve blocks today are performed using ultrasound guidance, as this technology allows direct visualization of local anesthetic spread around neural structures or between muscle and/or fascial layers. Nerve stimulation is an older technique that can be used alone or in conjunction with ultrasound, especially when anatomic structures are difficult to identify on ultrasound. Finally, some blocks can be performed using anatomic landmarks alone or via subcutaneous infiltration, resulting in a field block.

6

Describe the ultrasound guided nerve block technique and its advantages/disadvantages.

Ultrasound-guided nerve blocks are performed using ultrasound images to guide needle advancement and local anesthetic injection around neural structures. They may be performed using an in-plane (IP) or out-of-plane (OP) approach. Using the IP approach, the needle is advanced in the plane of the ultrasound beam, such that the entire shaft of the needle can be visualized. In contrast, the needle is advanced perpendicular to the ultrasound beam during the OP approach. This approach still allows for visualization of local anesthetic spread, but only a cross section of the needle, will be seen ( Fig. 68.1 ). In general, the IP approach is preferred because it shows the entire trajectory of the needle and more easily allows for avoidance of important structures, such as blood vessels, pleura, nerves, and so on. However, the OP approach can be useful because of its shorter and more direct path to the nerve.

Use of ultrasound allows for better visualization of anatomic structures, which has been shown to decrease the incidence of certain complications. With ultrasound it is possible to visualize blood vessels, thus allowing for a needle trajectory that decreases the risk of bleeding and hematoma formation. It also allows for visualization of the pleura, greatly reducing the risk of pneumothorax risk of supraclavicular block. Ultrasound is also useful in identifying anatomical variations that might limit the effectiveness of a given block technique; for example, it is possible to see muscles or blood vessels that split the target plexus and might prevent complete spread of local anesthetic. Lastly, it is possible to see the nerves themselves, ensuring that all neural structures are surrounded by local anesthetic and small branches are not missed. The major disadvantage to using ultrasound is that it requires specialized and expensive equipment that may not be available in all locations.

7

Describe the nerve stimulator technique and its advantages/disadvantages.

For this technique, a nerve stimulator device emits an electrical stimulus through an insulated block needle. The stimulus is generally short (0.05–1 ms) and repetitive (1–2 Hz), and the needle is advanced until muscle twitching and/or paresthesias, specific for the targeted nerve, are elicited. The intensity of the stimulus is then decreased until the twitching or paresthesia disappears. Continued response presence at low amplitudes signifies close proximity of the needle to the nerve. However, if a response is still elicited at an intensity of 0.3 mA, the needle is likely intraneural and should be withdrawn slightly before injecting local anesthetic. Note that muscle twitching tends to disappear once even small amounts of local anesthetic have been injected, and in some patients, twitching may not appear at all, even with excellent needle positioning.

Although the ability to elicit the appropriate muscle twitching response provides good confirmation of needle tip location, lack of visualization presents several challenges. Among these, are the possibility of unintentional nerve trauma and inability to identify variant anatomy. Also twitching can occur with direct muscle stimulation, which may be misidentified as nerve stimulation. For these reasons, the nerve stimulator technique is most often used in conjunction with ultrasound, and is of particular use in cases of difficult ultrasound visualization.

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