Moos, Daniel D. MS, EdD, CRNA
Anesthesia and analgesia continue to evolve: Ancient civilizations used medicinal plants such as the poppy, coca leaves, and mandrake roots. In 1855, Alexander Wood invented a syringe with a hollow needle, which allowed the administration of medications by additional routes not previously available. Cocaine was isolated from coca leaves the same year. Karl Koller is credited with using cocaine as a topical anesthetic in 1860 and William Halsted performed some of the first peripheral nerve blocks in 1884.1 These humble beginnings have led to the use of ultrasound-guided techniques for the administration of peripheral nerve blocks, the focus of this article. Peripheral nerve blocks may be administered without ultrasound guidance, but this technology is becoming increasingly common.
This article describes some common peripheral nerve blocks that may be administered for anesthesia or postoperative analgesia, either as a single injection or through a continuous catheter. The blocks described are upper extremity blocks of the brachial plexus, I.V. regional anesthesia, transversus abdominis plane (TAP) block of the trunk, and lower extremity blocks of the femoral and sciatic nerves.
Although ultrasound technology was first described for medical uses in the 1940s, the first report of ultrasound being used in conjunction with a peripheral nerve block didn't occur until 1978.2 Since then, the technology has become increasingly accepted among anesthesia providers. To briefly review, an ultrasound transducer or probe creates sound waves through piezoelectric crystals. These sound waves are projected into the tissue, bounce off the tissue or organ like an echo, and are reflected back to the ultrasound transducer. Tissues vary in their ability to reflect sound waves back to the transducer, so anesthesia providers may need to use different transducers for different parts of the body. The depth of -anatomic structures affects the overall quality of the ultrasound image—the closer a structure is to the surface, the better the image quality, and the deeper the structure, the lower the image quality.3
High-frequency linear array transducers (with a frequency of 10 to 12 MHz) are used for superficial structures that are generally less than 4 cm (1.6 inch) in depth, such as the brachial plexus and the femoral nerve. A low-frequency curved array transducer (frequency of 2 to 5 MHz) is used to identify anatomical structures that are deeper than 4 cm, such as the sciatic nerve. Medium-frequency transducers generally have a frequency of 6 to 10 MHz, and aren't commonly used because low- and high-frequency transducers are adequate for most peripheral nerve blocks.4
Anesthesia providers exert a great deal of control in improving visualization of structures by manipulating the transducer. When assisting with the placement of a peripheral nerve block, the OR nurse may be asked to adjust some of the controls on the ultrasound machine to help improve the overall image. A few basic controls are frequency, gain, depth, and color Doppler.
* Frequency is primarily determined by the anesthesia provider choosing the correct transducer. Finer adjustments may be made by manipulating the frequency setting on the ultrasound during the block to improve resolution of the target structure.
* Adjusting gain will lighten or darken the image by changing amplification of returning sound waves (also known as echoes). An increase in gain brightens the image and increases artifact; decreasing gain darkens the image.
* Adjusting the depth adjusts the image on the screen so that the target anatomy is clearly seen. Depth is usually increased or decreased.4 The perioperative nurse should slowly adjust these settings to help optimize the image.
* The color Doppler function helps clinicians identify vascular structures such as the internal jugular artery (see Color Doppler image). Anesthesia providers will often place pressure on a transducer to identify vascular structures. Arteries will appear as round, pulsating structures that aren't easily compressed; veins can be compressed by the application of pressure. A red image indicates that blood flow is traveling toward the transducer; blue indicates blood is traveling away from it.3
Ultrasound transducers must be kept sterile during the placement of peripheral nerve blocks to avoid infection. For a single-injection block, the anesthesia provider may choose to use sterile occlusive, transparent dressings. After the -injection site has been prepared with antiseptic -solution and draped with sterile drapes, the perioperative nurse holds the transducer in an upright position and applies transducer gel to the surface. The anesthesia provider then places the sterile occlusive transparent dressings on the transducer using sterile technique (see Preparing a transducer for a single-shot technique). Additional sterile transducer gel will be applied to the injection site.
Figure. Color Dopple...Image Tools
Alternatively, a sterile sleeve may be used over the transducer for either a single-shot injection or catheter insertion. The anesthesia provider prepares the injection site with antiseptic solution and drapes it with a sterile barrier. The perioperative nurse holds the transducer in an upright position and applies transducer gel to the surface or within the sterile sleeve while the anesthesia provider holds the sleeve, maintaining sterility. The anesthesia provider prepares the sleeve for application over the transducer by grasping the transducer with the sleeve and pulling the sleeve over the probe while maintaining sterile technique. Sterile rubber or non-latex bands are applied to keep the sleeve tight around the transducer.
Peripheral nerve stimulators
A peripheral nerve stimulator may be used -during the placement of a single-shot injection or catheter for continuous analgesia in the postoperative period. These devices may be used in conjunction with ultrasound or as a stand-alone technique. Nerve stimulators use low-intensity stimulation of the nerve and subsequent motor response of the muscles to aid in the placement of a peripheral nerve block or catheter. Tell the patient that this technique generally isn't uncomfortable, and that involuntary muscle movement is normal.
A stimulator has a positive lead (anode) that attaches to the ECG patch and a negative lead (cathode) that attaches to the needle. Be sure that the ECG patch is securely attached to the skin so that it can maintain conductivity; interrupting the current between the positive and negative electrodes could cause patient injury.
Figure. Preparing a ...Image Tools
Peripheral nerve stimulator configurations vary by manufacturer, but have three basic parameters: milliseconds (ms), which determine the duration of stimulation; hertz (Hz), which determine the frequency of stimulation; and milliamperes (mA), which determine the intensity of stimulation. The anesthesia provider sets the initial ms, Hz, and mA settings.5 The OR nurse may be asked to increase or decrease the intensity (mA) as the anesthesia provider localizes the target nerve.
A number of continuous catheters are manufactured for administering postoperative analgesia. Stimulating catheters are used in conjunction with peripheral nerve stimulators or ultrasound, or may be placed without peripheral nerve stimulation but with the assistance of ultrasound. These catheters have centimeter markings similar to epidural catheters, and a negative lead that attaches to the needle for initial localization. The negative lead is then attached to the catheter as it's inserted, and is attached to an injection port for final confirmation of catheter placement. Be sure the ECG patch (positive lead) is tightly connected to the nerve stimulator.
Peripheral nerve blocks: Upper extremity
A number of peripheral nerve blocks may be administered for upper extremity anesthesia or analgesia, and include nerves derived from the brachial plexus. Approaches to the brachial plexus include the use of known anatomical landmarks, eliciting a paresthesia with a blunt needle, nerve stimulation, and ultrasound-guided techniques. When eliciting a paresthesia, the anesthesia provider will use a B-bevel needle to come in close proximity to the nerve. The patient will feel a paresthesia in that nerve distribution. With the advent of newer technology (and because of the risk of sharp needles injuring the nerve), this technique is no longer common.
The overall success rate of the nerve block varies by approach and individual anesthesia provider experience. Ultrasound has been found to have a greater rate of success and lead to a faster onset of sensory blockade when compared with other techniques.6
The anesthesia provider determines which approach to take based on the site of surgical intervention, individual expertise, and patient-related factors.5 Peripheral nerve block is contraindicated in patients with a active infection at the site of the block, coagulation disorder, or those with neuropathy. The duration of the block depends on a -variety of factors, including the type of local -anesthetic used.
Figure. Brachial ple...Image Tools
The brachial plexus is a relatively complicated anatomical structure formed by the ventral branches of cervical (C5-C8) and thoracic (T1) spinal nerves, with some contributions from C4 and T2 (see Brachial plexus anatomy). These structures start as trunks as they leave cervical foramina and then come together and separate to form divisions, cords, and eventually main branches. At the anterior and middle scalene muscles trunks are formed and course over the lateral border of the first rib and under the clavicle. Each trunk will separate into anterior and posterior divisions. As the brachial plexus emerges under the clavicle, the divisions form three cords. When the brachial plexus reaches the pectoralis minor muscle, each cord will divide into branches and end as individual nerves.5
Each of the following approaches can be used for single-shot or catheter techniques, and can be used with paresthesia, nerve stimulation, or ultrasound techniques. For a recap of the nurse's role, see Summary of nursing actions for peripheral nerve block placement.
* The interscalene approach for a peripheral nerve block in the upper extremity is indicated for surgical procedures involving the shoulder, arm, and forearm because local anesthetic is deposited primarily at the C5-C7 distributions with a decreased block at C8-T1 (see Interscalene ultrasound anatomy).
This approach isn't used if the surgical procedure involves the ulnar nerve distribution.7 Because the local anesthetic is deposited close to the phrenic nerve, the interscalene approach shouldn't be used in patients with pulmonary disease.5,7
Patients are positioned supine with their head turned to face away from the surgical side and the shoulder relaxed to improve access. Complications of the interscalene approach include local anesthetic toxicity; phrenic and recurrent laryngeal nerve blockade, which may lead to a hoarse voice and dyspnea; Horner syndrome (myosis, ptosis, and anhidrosis); neuraxial blockade; and pneumothorax. A hoarse voice and Horner syndrome are common but self-resolve as the local anesthetic wears off, so tell patients before the procedure.
* The supraclavicular approach deposits local anesthetic in a more even distribution compared with the interscalene approach, resulting in excellent anesthesia and analgesia of the upper arm, forearm, and hand. This approach isn't a good choice for surgical procedures of the shoulder.7
Patients are positioned supine with their head facing away from the surgical side at a 30-degree angle. This approach should be avoided in patients with severe pulmonary disease. Complications include local anesthetic toxicity, pneumothorax, hemothorax, Horner syndrome, and phrenic nerve blockade.5,7
* The infraclavicular approach blocks the brachial plexus at the level of the lateral, posterior, and medial cords formed when the brachial plexus travels past the first rib. This approach results in anesthesia of the upper arm, forearm, and hand, and isn't a good choice for shoulder procedures.7
Patients are positioned with their head turned slightly to the side away from the operative limb. The arm may be abducted or placed down at the patient's side.
Figure. Interscalene...Image Tools
Complications of this approach include local anesthetic toxicity; pneumothorax and hemothorax, which may occur at a higher incidence compared to the supraclavicular approach; and chylothorax, with left-sided approaches.5,7
I.V. regional anesthesia
A technique first described in 1908, I.V. regional anesthesia, also called a Bier block, doesn't require modern technology such as ultrasound or peripheral nerve stimulators. Although it's a simple block when performed properly, it can be dangerous if done improperly or with faulty equipment. In this block, an I.V. injection of preservative-free 0.5% lidocaine is used to anesthetize the hand and lower arm, rather than blocking individual nerves. Using preservative-free lidocaine suitable for I.V. regional anesthesia is crucial—the use of any other local anesthetic solution could cause cardiac arrest.
This block is performed in the OR with the assistance of the OR nurse. The patient should have I.V. devices in the dorsum of the operative hand and in the nonoperative hand. The patient's operative arm is padded and a double pneumatic tourniquet is applied, and exsanguination occurs from the hand to the tourniquet with an elastic bandage. The proximal cuff is inflated then the distal cuff (by the anesthesia provider, or according to the provider's directions), followed by deflation of the proximal cuff. The elastic bandage is removed from the patient's arm. After confirmation of an absent pulse, the I.V. catheter is injected with an appropriate dose and volume of 0.5% preservative-free lidocaine as determined by the anesthesia provider. The catheter is then removed and the arm prepped for surgery.
The pneumatic tourniquet should be inflated for a minimum of 25 minutes so that the drug can be absorbed into the tissues and to prevent the local anesthetic from rushing into the circulation, causing local anesthetic toxicity. If the patient complains of tourniquet pain during the procedure, the distal cuff can be inflated and the proximal cuff deflated. Because the patient can tolerate a tourniquet for a short period, I.V. regional anesthesia is limited to procedures that take fewer than 60 minutes.
When the procedure is completed and the cuff is deflated, monitor the patient for signs and symptoms of local anesthetic toxicity, which include lightheadedness, tinnitus, paresthesia, seizure, cardiovascular depression with hypotension, bradycardia, ventricular dysrhythmias, and respiratory arrest. The most common complications of this block include local anesthetic toxicity from early deflation of the tourniquet or tourniquet malfunction, and tourniquet pain. Once the tourniquet is deflated the patient will regain sensation. Encourage the surgeon to infiltrate the operative area with local anesthetic, if appropriate, after closing the wound.5,7–8
Peripheral nerve blocks: Trunk
The TAP block is a useful peripheral nerve block of the abdomen for postoperative analgesia of the lower anterior abdominal wall when an epidural isn't desirable. A number of thoracolumbar nerves (T8-L1) can be blocked at the Petit triangle, which is located superior to the iliac crest and bordered by the latissimus dorsi and external abdominal oblique muscles. The thoracolumbar nerves are located between the transversus abdominis muscle and internal oblique.9,10
TAP blocks can be placed with or without ultrasound. Advantages of ultrasound over traditional methods include being able to visualize anatomical structures at the Petit triangle, so the anesthesia provider can see the needle and avoid intraperitoneal placement, as well as confirm correct placement of local anesthetic.11 TAP blocks often are placed while the patient is anesthetized in the OR.
For this block, patients are positioned supine or in a lateral decubitus position. Sterile towels, drapes, and prep solution are needed. If the abdominal incision is midline, a bilateral TAP block is performed. If the surgery affected only one side of the abdominal wall, then a single injection may be performed. The OR nurse may be asked to make fine adjustments to the ultrasound machine and assist with injecting small amounts of local anesthetic as the anesthesia provider identifies each muscle plane for proper placement of the local anesthetic.
Complications of a TAP block include local anesthetic toxicity because of the volume and concentration of local anesthetic required for bilateral TAP blocks and the vascular structures located within the abdominal wall; hematoma formation; and needle trauma or anesthetic injection into abdominal structures.9,10
Peripheral nerve blocks: Lower extremity
Two types of lower extremity blocks, femoral and sciatic nerve blocks, can provide anesthesia and analgesia to the lower extremities. Most surgical procedures require a combination of nerve blocks to ensure surgical anesthesia. Because neuraxial blockade offers reliable anesthesia and is simple to administer, peripheral nerve blocks of the lower extremity are often used for postoperative analgesia. Ultrasound lets the anesthesia provider see anatomical structures, needle placement, and local anesthetic spread. As a result, analgesia can take effect more quickly, with less sensory and motor blockade, and less local anesthetic needed for femoral nerve blocks. Ultrasound guidance for sciatic nerve blocks also decreases local anesthetic requirements and time to perform the block, as well as providing for a faster onset and improved success rate.12
* The femoral nerve innervates the anterior thigh and knee, making a femoral nerve block appropriate for any surgical procedure of the thigh and anterior knee. The femoral nerve is formed from contributions of L2, L3, and L4 and is the largest branch -originating from the lumbar plexus. The femoral nerve enters the thigh under the inguinal ligament, between the psoas and iliacus muscle, and is located below the fascia iliaca.5,7,13
Often, a femoral nerve block is combined with additional nerve blocks to provide more complete analgesia because the obturator and sciatic nerve also innervate the lower extremities. Femoral nerve blocks may be placed as a single injection or continuous infusion. When placing a pneumatic tourniquet, transferring a patient, or during sterile preparation of the limb, be sure that the catheter is intact and won't be inadvertently dislodged. Place a knee immobilizer on the operative limb before ambulation.
Femoral nerve blocks weaken the patient's ability to contract the quadriceps, which may predispose patients to falls. Preoperatively, be sure to tell the patient about postoperative leg muscle weakness and advise the patient to ambulate only with assistance until the block wears off. Femoral nerve blocks have a relatively low -incidence of complications. Complications include local anesthetic toxicity, vascular puncture and hematoma formation, and nerve injury.5,7,13
* A sciatic nerve block may be combined with a femoral nerve block for procedures of the knee. The sciatic nerve is formed by the nerve roots of L4, L5, S1, S2, and S3. This very large nerve provides sensory input to the hip joint, knee, and below the knee (with the exception of the medial aspect of the ankle and foot). The sciatic nerve also provides motor input to the hamstring muscles in the upper leg and all of the muscles below the knee.7 Procedures below the knee can be easily blocked with a sciatic nerve block; a supplemental saphenous nerve block will be required if surgery involves the medial aspect of the foot or ankle.
A single-injection technique is often used, though peripheral nerve catheters may be placed. Sciatic nerve blocks may be placed with peripheral nerve stimulators or ultrasound. Approaches to the sciatic nerve are based on the anesthesia provider's preference and may include a supine position for an anterior approach and a lithotomy or lateral decubitus position for a posterior approach. The sciatic nerve may be blocked above the popliteal fossa as it divides into the common peroneal and tibial nerves. This is known as a popliteal block.
Because of its anatomical position and relatively poor blood supply, the sciatic nerve is prone to injury. Sciatic nerve blocks generally aren't used in patients with a history of diabetes or peripheral neuropathies. Epinephrine-containing solutions are avoided because they can exacerbate nerve ischemia.
Avoid direct compression on the injection site when placing a pneumatic tourniquet or positioning a patient with a sciatic nerve block. Careful attention to tourniquet inflation pressures and maximum inflation times are important to avoid potential complications. In addition to the risk of nerve trauma, the patient is at risk for local anesthetic toxicity, especially if the sciatic nerve block was combined with other peripheral nerve blocks.5,7,13
By understanding the technology that may be involved during placement of a peripheral nerve block, and the indications, complications, patient management, OR nurses can help patients have a good surgical experience.
Summary of nursing actions for peripheral nerve block placement3–5,7,8,13–16
* Follow the Universal Protocol and label medication preprocedure.
* Follow standard precautions.
* Have resuscitation equipment immediately available.
* Help the anesthesia provider position the patient.
* Administer sedatives as directed by the anesthesia provider.
* Reassure the patient during administration of the peripheral nerve block.
* Help maintain sterility during preparation of the injection site and the ultrasound transducer.
* Adjust the ultrasound controls as needed to help improve visualization.
* Ensure adequate ECG contact with the patient's skin for positive lead and connection of negative lead to the needle when using peripheral nerve stimulator.
* Adjust the intensity of the peripheral nerve stimulator, if used, when identifying the nerve.
* Reassure the patient that involuntary muscle movement is normal when using a peripheral nerve stimulator during block placement.
* Assist the anesthesia provider in monitoring the patient during and after peripheral nerve blockade.
* Avoid placing a pneumatic tourniquet directly over the sciatic nerve injection site.
* Have a functioning and reliable double pneumatic tourniquet available for I.V. regional anesthesia.
* Monitor the patient recovering from a peripheral nerve block as you would monitor any patient recovering from anesthesia.
* Protect the insensate limb after block placement.
* Monitor the patient for block-specific complications.
* Ensure that peripheral nerve catheters are connected and secured.
* Check the peripheral nerve catheter and insertion site during routine nursing care.
* Ensure that sterile dressings are intact.
* During patient transfers, avoid accidental dislodgement of the catheter.
* Tailor patient teaching to the specific block and expected duration of blockade.
© 2011 Lippincott Williams & Wilkins, Inc.