26: PERIPHERAL AND CENTRAL NEURAXIAL BLOCKS IN CRITICAL CARE MEDICINE

Introduction

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.

Equipment

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 ...