The role of neuraxial blocks and peripheral nerve blocks in the critical care setting has vastly improved due to the use of ultrasonography. Despite the available technology, the use of these techniques in critical care remains rare. This chapter will provide examples of current and potential uses for the use of central and peripheral nerve blocks using ultrasound in a critical care setting.
Although the physics and the use of equipment have been described previously (Chapter 2), specific discussion of the use of particular transducers for certain procedures is important. The use of a linear probe can help to localize nerve using ultrasonography. Sterile precautions should always be exercised prior to the performance of these blocks. Although the use of a sterile sheath can be very helpful, in an acute setting, a sterile Tegaderm can be used to cover the probe and effectively place nerve blocks in an intensive care unit (ICU). Nerves can appear anechoic, hypoechoic, or hyperechoic, depending on the particular plexus. Unlike vascular structures, they are not always hypoechoic and, therefore, color is unable to delineate them. A portable ultrasonography machine that can be brought to the patient’s bedside to scan the patient and place the blocks is most useful in the ICU. Although sedation may be required in some instances, especially if infants and children are involved, most blocks can be performed with the superficial subcutaneous injection of local anesthetic. The advantage of ultrasonography is the ability to have a single pass directly to the proximity of the nerve structure and provide the block without the need for nerve stimulation. Nerve blocks are performed for a variety of reasons in the ICU, including diagnostic reasons, pain control, and managing vascular insufficiency (Table 26-1).
Local Anesthetic Solution
Any long-acting local anesthetic solution, mostly amides, are used for pain control using a regional anesthetic technique.1 Although the commonly used, long-acting, local anesthetic bupivacaine is a dextroenantiomer and may have greater cardiovascular toxicity compared with the levoenantiomer, it is still routinely used in most clinical practices.2,3 The dose of local anesthetic solution has to be contained within the toxic dosage allowable. A dose of <4 mg/kg will ensure a reasonable degree of safety, although careful aspiration should be carried out prior to injection. Ultrasonography has advanced our ability to identify vascular structures prior to injection. Newer levoenantiomers, ropivacaine, and levobupivacaine, although safe, cannot be considered completely immune to the cardiovascular and neurotoxicity of local anesthetic solutions. A detailed description of local anesthetics and their toxicity can be found in many standard pharmacology and anesthesia textbooks. A rule of thumb is that toxicity varies for different blocks decreasing in the progression from intercostal block, caudal blocks, epidural blocks, to peripheral nerve blocks. Local anesthetic toxicity includes seizures and cardiovascular collapse. A newer modality of treating the toxicity with intravenous intralipid is gaining popularity.4 In the ICU, it may be reasonable to have the availability for lipid rescue in the event there is accidental injection of local anesthetic solution into the intravascular compartment.
Central Neuraxial Blocks
Central neuraxial blocks are performed for diagnosis or for pain control. A common central neuraxial procedure in the ICU is a diagnostic lumbar puncture. Although this can be performed with ease in most patients, the depth of the epidural space and the dura from the skin may be difficult to ascertain both in younger populations, such as in infants and children,5 and in the obese older patient, particularly in the obstetrical suite. The use of ultrasound may be a helpful diagnostic tool to determine the exact depth of the epidural space and the dura in children and adults.6,7 Although the curvilinear probe may be helpful in the older adult, a transverse probe capable of scanning deeper (7 MHz) may be helpful in children and infants. The epidural and dural area can be scanned for depth using a transverse axial approach and in a sagittal longitudinal plane. A cadaver-based teaching model for ultrasonography has recently been described for learning ultrasound imaging for central neuraxial sonoanatomy.8 It is important to understand that the transverse axial plane can be used to discern the sonoanatomy of the vertebral column, while the longitudinal sagittal plane can be used for recognizing the spinous, articular, and transverse processes. Real-time use of the sonoanatomy for placement of epidural catheters can be applied in children, where there is less calcification and an improved ability to visualize structures.7 The use of epidural analgesia for pain control has traditionally been reserved for patients in the postoperative period. The use of this technique for pain control in the ICU has been reported anecdotally for vascular insufficiency by providing a sympathetic blockade.9 Epidural analgesia can be provided for pain control following vascular crisis in sickle cell disease in an intensive care setting.10
The technique for epidural analgesia is presented in Figure 26-1.
Place the ultrasound probe between the spinous process.
Determine the location of the spinous and transverse processes.
Gently slide the probe cephalad or caudad until the dura and the epidural space can be located.
Use the depth indicator to measure the exact distance of the epidural space from the skin.
Mark the ends of the probe bilaterally and in the midline.
A line intersecting these two lines will provide a point of entry of the needle.
The exact distance for the needle to enter into the epidural space to the predetermined area allows the operator to advance the needle to the specified depth.
If real-time ultrasonography is used, it is imperative to use loss of resistance with saline or local anesthetic solution for determining the depth of the space.
Upper Extremity Blocks
The brachial plexus supplies the pain fibers to the upper extremity. It is derived from the cervical roots C5, C6, C7, C8, and T1. It is important to understand the multiple approaches to the brachial plexus for a variety of surgical procedures, depending on the area that is being operated on (Table 26-2). This technique can also be used for pain relief in critically ill trauma victims in the ICU.11 This block has the advantage of increasing blood supply, thereby potentially improving perfusion to the compromised upper extremity.12 The approach to the brachial plexus is at the interscalene (roots), supraclavicular (trunks), infraclavicular (divisions and cords), and axillary (branches) levels of the brachial plexus in the arm (Tables 26-2 and 26-3).13,14 If an indwelling catheter is placed for trauma or vascular insufficiency, we prefer using the infraclavicular approach.15,16 The supraclavicular approach is an easier approach, especially if there is significant trauma in the upper extremity, because this can reduce arm movement during performance of the block. The ultrasound technique for each one of these approaches is well described. Often, operator preference determines the approach used. We tend to use the supraclavicular approach for most fractures. For larger limb salvage procedures that require multiple days of intense pain control, an indwelling infraclavicular approach is preferred. The volume of local anesthetic solution varies, depending on the access. For most pain control, however, a volume of 15 mL of local anesthetic solution (0.2% ropivacaine or 0.25% bupivacaine) can provide adequate analgesia. In children, a dose of 0.2 mL/kg of local anesthetic solution is used.