1 What are the advantages of peripheral nerve blocks?

Peripheral nerve blocks (PNBs) share many of their advantages with neuraxial (spinal and epidural) anesthetic and analgesic techniques, first of which is the lack of need for airway instrumentation. This feature makes PNBs useful in cases in which airway management will be difficult or in which the patient has borderline respiratory function. PNB allows for shorter discharge times in ambulatory settings because of the decreased incidence of nausea, vomiting, and severe pain. PNB may diminish or prevent the development of chronic pain syndromes because of the lack of central nervous system sensitization that occurs after acute injury. Finally, patients with PNB have minimal if any opioid requirements in the immediate postoperative phase.

2 What basic principles should be followed to ensure a safe and successful peripheral nerve block?

Patients should be informed about the potential risks and benefits of PNB and allowed to decide on the anesthetic they prefer. Not all patients are good candidates for regional anesthetics. For example, performing PNB after high-velocity trauma to a lower extremity might obscure the diagnosis of a compartment syndrome. Sedation should be carefully titrated while performing a PNB because the patient should be able to communicate and give feedback to the clinician. This helps in confirming correct needle placement and giving an early warning of local anesthetic toxicity.

The clinician must have knowledge of the anatomy, technique, and equipment necessary to perform the most appropriate block for a given situation. The use of aseptic technique, correct equipment (B-bevel needles, nerve stimulators, ultrasound), and basic physiologic monitoring is mandatory. The area in which the PNB is performed should have immediate access to resuscitative equipment and medications.

3 What are the risks of performing a peripheral nerve block?

There may be inadvertent damage to anatomic structures by the advancing needle. Examples include direct trauma to the nerve or spinal cord by intraneural injection of local anesthetic, nerve laceration, vascular injury with resulting hematoma formation, or pneumothorax.

The drugs that are injected may have undesirable local and systemic effects. Allergic reactions to local anesthetics are rare. Ester local anesthetics are derivatives of para-aminobenzoic acid, a known allergen, and therefore more likely to cause allergic reactions than the amide local anesthetics. Any local anesthetic injected intravascularly has the potential for systemic reactions, including seizures and cardiovascular collapse.

4 How can the risks from a peripheral nerve block be minimized?

It is essential to ensure correct needle placement. Knowledge of the anatomy of the target region and the surrounding structures is necessary. Knowledge of the equipment and the pharmacology of local anesthetics is also required. Do not perform a PNB with which you are unfamiliar or not trained to do.

5 Describe a good technique for advancing the needle and injecting the local anesthetic solution

Continuous aspiration is mandatory while advancing the needle; flow of blood or cerebrospinal fluid is an obvious sign that the needle needs to be redirected and the landmarks reevaluated. Be attentive to reports of symptoms experienced by the patient. A paresthesia indicates close proximity to a nerve; and, depending on the technique being used, it might constitute the end point.

Once it is determined that the needle is correctly positioned, a 1-ml test dose is administered. Severe pain during injection might be a sign of intraneural needle placement. Evidence suggests that monitoring the injection pressure is useful in preventing intraneural injection. After the test dose is administered, slow incremental injection of the local anesthetic solution is started. This is a very important safety feature since it allows recognition of signs of local anesthetic toxicity before cardiac collapse occurs.

6 How are peripheral nerves localized?

Use of anatomic landmarks allows precise identification of correct skin insertion sites. After the needle is inserted, the nerves are localized by nerve stimulation. The clinician looks for a known motor response during electrical stimulation of 0.5 mA or less to signal correct needle position. A paresthesia of the targeted nerve is another useful identifying sign. Finally, with the use of ultrasound, the known relationship of nerves to other anatomic structures such as blood vessels and fascial planes allows for nerve localization.

7 Is one technique to localize nerves better or safer than any other?

Improvements in ultrasound equipment have made ultrasonic guidance more popular over the past few years. The safety of PNB may also have been improved by the introduction of ultrasound, although no study has demonstrated this. In experienced hands there seems to be no significant difference between nerve stimulator and landmark techniques and ultrasound-guided PNB in terms of success rate or complications. It is my belief that, if nothing else, ultrasound guidance is responsible for a resurgence of interest in regional anesthesia in many anesthesia practices.

8 When using ultrasound guidance, what is the difference between an in-plane and an out of-plane approach?

The in-plane approach means that the shaft of the needle is visualized while the needle is advanced (Figure 67-1). This technique allows the operator to observe the tip of the needle as it advances through the different anatomic structures. The out-of-plane approach relies on known anatomic relationships and careful injection (which can be observed in real time) to evaluate the adequacy of needle placement. In the out-of-plane approach the short axis (transverse cut) of the needle is visualized.

Figure 67-1 A good example of an in-plane approach. Note the needle shaft and tip as it comes in contact with the brachial plexus between the anterior scalene muscle (ASM) and the middle scalene muscle (MSM).

9 Review upper-extremity nerve blocks, including their indications, limitations, and complications

See Table 67-1. The volumes of local anesthetic solutions for an adult are between 20 and 30 ml.

10 What is the Bier block and how is it performed?

The Bier block is also known as intravenous regional anesthesia. It is mostly used for anesthesia of the wrist and hand and usually for nonosseous procedures such as carpal tunnel release, trigger finger release, and ganglion resection. The Bier block works by local anesthetic diffusion from the intravenous space to the nerve fibers that travel in the vicinity of the veins in the upper extremity. The duration of the Bier block is up to 90 minutes, has a high patient satisfaction, and allows for rapid discharge of the patient.

The first step in performing a Bier block is securing intravenous (IV) access to the limb that is to be anesthetized. (The patient should also have an IV line in the opposite extremity for administration of fluids and medications.) A small-gauge needle is enough, but care should be taken to place the IV line as distally as possible, usually in the back of the hand. A double tourniquet is placed around the upper arm. The arm is exsanguinated by elevating and wrapping it tightly with a wide elastic (Esmarch) band. The distal then proximal tourniquet is then inflated to 250 mm Hg. The Esmarch is removed, the distal tourniquet cuff is then deflated, and 40 to 50 ml of 0.5% lidocaine is injected through the IV line. Anesthesia sets in within minutes, and the surgical procedure might begin.

11 How is local anesthetic toxicity avoided when performing a Bier block?

Local anesthetic toxicity will happen if the injected local anesthetic solution rapidly enters the central circulation. Local anesthetics can only gain access to the circulation if the tourniquet cuffs are purposefully or accidentally deflated. The anesthesiologists should have immediate access to the tourniquet, tubing, and pressuring device being used while performing a Bier block. Tubing should be secured and situated to avoid any accidental disconnection.

If the procedure lasts less than 30 minutes, the tourniquet is slowly and repeatedly deflated and reinflated. The brief deflations allow some of the local anesthetic into the circulation. The patient is quizzed for signs of local anesthetic toxicity. Perioral numbness, a metallic taste, and ringing in the ears are common early symptoms of mild toxicity. Should they occur, they should be allowed to resolve before further local anesthetic is released centrally. This should prevent more severe manifestations of local anesthetic toxicity such as seizures and cardiovascular collapse. Other mild symptoms include disinhibition as manifested by agitation and/or tearfulness.

12 What peripheral nerve block can be performed for surgery of the lower extremity?

The first step in deciding what block is indicated for anesthesia or analgesia is appreciating the innervation of the lower extremity and the requirements of the proposed procedure. The lumbar plexus (L1-L4) gives origin to the ilioinguinal, genitofemoral, obturator, femoral, and lateral femorocutaneous nerves and mainly innervates the inguinal region and the anterior aspect of the thigh. The rest of the lower extremity is innervated by the sacral plexus. This includes the posterior aspect of the thigh and all the area distal to the knee except for the medial aspect, which is the territory of the saphenous nerve, a branch of the femoral nerve. The main nerve arising from the sacral plexus is the sciatic nerve. The sciatic nerve is actually formed by union of the tibial and peroneal nerves. These two nerves separate in or slightly above the cephalad region of the popliteal fossa. Table 67-2 describes the most common indications, limitations, and complications of the most commonly performed PNB to the lower extremity.

13 What peripheral nerve block can be used to provide anesthesia or analgesia to the chest wall?

A thoracic paravertebral block can be performed to provide anesthesia for breast procedures such as lumpectomy or total mastectomy. Thoracic paravertebral analgesia is also used in patients undergoing VATS procedures and in patients with multiple unilateral rib fractures as an alternative to thoracic epidural catheter placement.

14 What peripheral nerve block can be used to provide anesthesia or analgesia to the anterior abdominal wall?

Anesthesia or analgesia to the lower quadrants or the inguinal region can be accomplished by performing intercostal blocks at the last three levels or blocking the genitofemoral and the ilioinguinal nerves. A more recently described approach, the transverse abdominis plane (TAP) block, is reported to cover the entire anterior abdominal wall, making it very useful in patients in whom epidural analgesia is impractical. TAPS block requires ultrasound guidance to ensure correct needle placement.