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Peripheral Nerve Blocks
INTRODUCTION
The Role of Regional Anesthesia
Peripheral nerve blocks can provide surgical anesthesia and postoperative pain relief ( Table 18.1 ). The main emphasis of this chapter will be on ultrasound guidance for peripheral nerve blocks. However, paresthetic-based techniques and nerve stimulation also are possible for nerve localization. In addition, ultrasound guidance and nerve stimulation technologies can be combined for some regional blocks.
Table 18.1
Examples of Peripheral Nerve Blocks
Preparation to Perform a Regional Nerve Block
Foundation of Knowledge
To perform safe and effective peripheral nerve blocks, an understanding of peripheral neuroanatomy, ultrasound technology, local anesthetic pharmacology, and risks associated with peripheral nerve blocks is needed.
Patient and Surgeon Factors
The willingness of the patient and the surgeon, in addition to the anatomic location of the surgery, must be taken into consideration when incorporating peripheral nerve blocks into an anesthetic plan. A thorough preoperative review of the patient's medical history, including any comorbid diseases, allergies, prior neuropathy, and concurrent anticoagulation medications, must be performed to rule out any contraindications in providing a peripheral nerve block.
Monitors and Equipment
Peripheral nerve blocks may be performed preoperatively in a dedicated block area or in the operating room. The patient must have a functional peripheral intravenous line and monitoring equipment, including pulse oximetry, electrocardiogram (ECG), and noninvasive blood pressure machine. Supplemental oxygen, emergency medications, and airway equipment must be readily accessible. Sedation may be indicated, depending on the patient's anxiety and magnitude of pain.
The patient, ultrasound machine, and anesthesia provider must be positioned in a way to optimize the nerve block being performed. For most blocks, the provider is positioned on the ipsilateral side and the ultrasound on the contralateral side of the block region. The choice of the ultrasound probe ( Fig. 18.1 ) and needle is dependent on the location of the peripheral nerve block; the addition of placing a catheter will depend on the type of surgery being performed, the duration of hospital stay, and patient and surgeon preference.
Choice of Local Anesthetic
The choice of local anesthetic for peripheral nerve blockade depends on several factors, including the desired onset, duration, and degree of conduction block (see Chapter 10 ). Lidocaine and mepivacaine, 1% to 1.5%, produce surgical anesthesia in 10 to 20 minutes that lasts 2 to 3 hours. Ropivacaine 0.5% and bupivacaine 0.375% to 0.5% have a slower onset and produce less motor blockade, but the effect lasts for at least 6 to 8 hours. The addition of epinephrine 1:200,000 (5 μg/mL) can serve as a marker for intravascular injection and can increase the duration of a conduction block. In addition, through a decrease in the rate of systemic absorption, epinephrine can reduce peak plasma levels of local anesthetic. Practitioners may also add perineural steroids (e.g., preservative-free dexamethasone) to local anesthetics to prolong regional blocks. Considerations for the choice of local anesthetic solution for intravenous regional anesthesia are different from those for peripheral nerve blocks (see the later discussion under “Intravenous Regional Anesthesia [Bier Block]”).
Regional Block Checklist
A standardized regional block checklist should be reviewed before performing a peripheral nerve block to improve safety. , The checklist should include surgical consent, site marking, allergies, anticoagulation status, proposed peripheral nerve block, local anesthetic dose, side of the block, monitors implemented, emergency equipment available, and sedation plan.
Risks and Prevention
Infection
Infectious risk associated with a peripheral nerve block or placement of a peripheral nerve catheter is rare. However, an infection can cause significant morbidity and may lead to permanent neurologic injury. By performing proper hand hygiene, using maximal barriers during nerve block and catheter placement, and providing antiseptic solution at the site of insertion, the rate of infection can be reduced.
Hematoma
The risk of developing a hematoma depends on the location of the peripheral nerve block being performed, the proximity to vascular structures, and vascular compressibility. With the use of ultrasound and proper aspiration technique, vascular puncture can be reduced. A review of the patient's medical history with an emphasis on any anticoagulation medications is important. The American Society of Regional Anesthesia and Pain Medicine provides guidelines on anticoagulation management.
Local Anesthetic Systemic Toxicity (Also See Chapter 10 )
Local anesthetic systemic toxicity (LAST) secondary to local anesthetic absorption can range from mild symptoms to major neurologic and cardiovascular toxicity. A variety of factors, including patient risk factors, concurrent medications, total local anesthetic dose, and anatomic location of the peripheral nerve block, play a role in the risk of LAST. There is no single measure to prevent LAST; however, using the smallest effective dose, an incremental injection, aspiration before injection, an intravascular marker (i.e., epinephrine), and ultrasound guidance may decrease the risk. Lipid emulsion resuscitation remains the cornerstone of therapy to treat patients with LAST. ,
Nerve Injury
Nerve injury may result from direct needle trauma, inadvertent intraneural injection, or drug neurotoxicity. Serious neurologic injury from a peripheral nerve block is rare; however, the rate of transient paresthesia that resolves within days to weeks postoperatively is substantially higher. – The use of ultrasound to identify nerves, limiting the injection pressure, and patient feedback may help decrease the rate of nerve injury, although clinical outcome data are limited.
Wrong-Sided Block
Wrong site, wrong procedure, and wrong patient peripheral nerve blocks are potentially serious medical errors that are inherent risks in performing any medical procedure. Although rare, this complication can be reduced by having a universal protocol that includes a checklist to ensure the correct patient, the proper surgery site, and correct laterality ( Table 18.2 ).
Table 18.2
Approximate Incidence of Adverse Events During Peripheral Nerve Blocks
| Adverse Event | Approximate Incidence |
|---|---|
| Anesthetic systemic toxicity | 1 in 2000 5 |
| Peripheral nerve injury | 1 in 1000 |
| Wrong side/site block | 1 in 10,000 |
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