Peripheral Nerve Blockade

Regional anesthesia enables site-specific, long-lasting, and effective anesthesia and analgesia (Tsui BCH, Rosenquist RW. Peripheral nerve blockade. In: Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Ortega R, Stock MC, eds. Clinical Anesthesia. Philadelphia: Lippincott Williams & Wilkins; 2013:937–995). Peripheral nerve blocks (PNBs) can be used as the only anesthetic, as a supplement to provide analgesia and muscle relaxation along with general anesthesia, or as the initial step in the provision of prolonged postoperative analgesia such as with intercostal blocks or continuous peripheral nerve catheters. The two most common techniques for nerve localization and block performance are nerve stimulation (NS) and ultrasound (US) imaging.

I. General Principles and Equipment

An exciting advance in technology in relation to regional anesthesia in recent years has been the introduction of anatomically based US imaging to visualize the target nerve. In many situations, it is prudent to combine the two technologies of NS and US imaging to achieve the goal of 100% success with all regional blocks.

Setup and Monitoring (Table 35-1)

Common Techniques: Nerve Stimulation

Basics of Technique and Equipment. A low-current electrical impulse applied to a peripheral nerve produces stimulation of motor fibers and theoretically identifies proximity to the nerve without actual needle contact of the nerve or related patient discomfort.

Practical Guidelines. After a low-threshold response is obtained, 2 to 3 mL of local anesthetic is injected, and the operator watches for disappearance of the motor twitch, which is a signal to inject the remainder of the
proposed dose in divided aliquots. After nerve localization using a stimulating needle, introduction of a stimulating catheter with continuous stimulation of the nerve is suitable for provision of continuous analgesia.

Table 35-1 Setup and Monitoring for Regional Blocks

Setup

All supplies located in this area must be readily identifiable and accessible to the anesthesiologist.

The area should be of ample size to allow block performance, monitoring, and resuscitation of patients.

There should be equipment for oxygen delivery, emergency airway management, and suction, and the area should have sufficient lighting.

A practically organized equipment storage cart is desirable and should contain all of the necessary equipment (including equipment required for emergency procedures).

A selection of sedatives, hypnotics, and intravenous anesthetics should be immediately available to prepare patients for regional anesthesia.

Emergency drugs (atropine, epinephrine, phenylephrine, ephedrine, propofol, thiopental, succinylcholine, amrinone, intralipid) should also be immediately available.

Monitoring

During the performance of regional anesthesia, it is vital to have skilled personnel monitor the patient at all times (electrocardiography, noninvasive blood pressure, pulse oximetry, and level of consciousness of the patient should be gauged frequently using verbal contact because vasovagal episodes are common with many regional procedures).

The patient should be closely observed for systematic toxicity (within 2 minutes for at least 30 minutes after the procedure).

Before performing blocks with significant sympathetic effects, a baseline blood pressure reading should be obtained.

Common Techniques: Ultrasound Imaging

Basics of Technique and Equipment. US images reflect contours, including those of anatomic structures, based on differing acoustic impedances of tissue or fluids. The Doppler effect can be very useful for identifying blood vessels during nerve localization using US guidance because many nerves are situated in close proximity to vascular structures.

Practical Guidelines

Probe sterility is paramount when performing real-time US guidance. For nerve localization during
US-guided PNB, it is effective to first identify one or more reliable anatomic landmarks (bone or vessel) with a known relationship to the nerve structure (Table 35-2). The nerve structure is often placed in the center of the screen to guarantee that aligning the needle puncture with the center of the probe will ensure close needle tip–nerve alignment.

Table 35-2 Useful Anatomical Landmarks for Localizing Nerves During Common Ultrasound-Guided Peripheral Nerve Blocks

Peripheral Nerve Block Location	Anatomical Landmark(s)	Approach for Ultrasound Imaging
Interscalene	Subclavian artery Scalene muscles	Locate the plexus or trunk divisions superolateral to the artery at the supraclavicular fossa and trace proximally to where the roots or trunks lie between the scalenus anterior and medius muscles.
Supraclavicular	Subclavian artery	Scan from lateral to medial on the superior aspect of the clavicle to locate the pulsatile artery. Plexus trunks or divisions lie lateral and often superior to the artery. Color Doppler is useful.
Infraclavicular	Subclavian and axillary artery Subclavian and axillary vein	Place the artery at the center of the field and locate the brachial plexus cords surrounding the artery.
Axillary	Axillary artery	Terminal nerves surround the artery.
Peripheral Nerves
Median nerve at the antecubital fossa	Brachial artery	The large anechoic artery lies immediately lateral to the nerve.
Radial nerve at the anterior elbow	Humerus at spiral groove Deep brachial artery	Trace the nerve proximally and posteriorly toward the spiral groove of the humerus, just inferior to the deltoid muscle insertion (the nerve is adjacent to the deep brachial artery).
Ulnar nerve at the medial forearm	Ulnar artery	Scan at the anteromedial surface of the forearm approximately at the junction of its distal third and proximal two thirds to locate the ulnar nerve as it approaches the ulnar artery on its medial aspect.
Lumbar Plexus	Transverse processes	The plexus lies between and just deep to the lateral aspect (tips) of the processes.
Femoral	Femoral artery	The nerve lies lateral to the artery (vein most medial). See Fig. 35-11.
Sciatic
Classical or Labat	Ischial bone and inferior gluteal or pudendal vessels	The nerve lies lateral to the thinnest aspect of the ischial bone. The inferior gluteal artery lies medial to and at the same depth as the nerve.
Subgluteal	Greater trochanter and ischial tuberosity	The nerve lies between the two bone structures.
Popliteal	Popliteal artery	Trace the tibial and common peroneal nerves from the popliteal crease to where they form the sciatic nerve. At the crease, the tibial nerve lies adjacent to the popliteal artery. Scanning proximally to the sciatic bifurcation, the artery becomes deeper and at a greater distance from the nerve.
Ankle
Tibial (posterior tibial) Deep peroneal	Posterior tibial artery Anterior tibial artery	The nerve lies posterior to the artery. The nerve lies lateral to the artery.

After one observes that the needle is seen to be close to the nerve(s), a 1- to 2-mL test dose of local anesthetic or dextrose 5% in water (D5W) can be injected to visualize the spread. The solution will be seen as a hypoechoic expansion and often illuminates the surrounding area, enabling better visibility of the nerves and block needle.

Other Related Equipment
- Needles used for regional techniques are often modified from standard injection needles. (Continuous blocks require larger bore needles to facilitate catheter introduction.)
- Catheters amenable to stimulation (with an electrode placed into the catheter tip) may enable more accurate advancement of catheters for substantial distances to provide continuous analgesia.
Avoiding Complications. Despite the excellent safety record of regional anesthesia, the incidence of some complications may be higher in PNB than other regional anesthesia or analgesia techniques, and these complications can be devastating. Choosing a suitable patient and applying the right dose of local anesthetic in the correct location are the primary considerations. Follow-up before and after discharge is equally important.