The incidence of complications from general anesthesia has diminished substantially in recent decades, largely due to advances in respiratory monitoring.1 The use of objective monitors such as pulse oximetry and capnography allows anesthesiologists to quickly identify changing physiologic parameters and intervene rapidly and appropriately.
In contrast, the practice of regional anesthesia has traditionally suffered from a lack of similar objective monitors that aid the practitioner in preventing injury. Practitioners of peripheral nerve blocks were made to rely on subjective end points to gauge the potential risk to the patient. This is changing, however, with the introduction and adoption of standardized methods by which to safely perform peripheral nerve blocks with the minimal possible risk to the patient. For example, instead of relying on feeling "clicks," "pops," and "scratches" to identify needle tip position, the anesthesiologist can now directly observe it using ultrasonography. It follows that advancements such as this may help in reducing the three most feared complications of peripheral nerve blockade: nerve injury, local anesthetic toxicity, and inadvertent damage to adjacent structures ("needle misadventure").
Objective monitoring, and the rationale for its use, is discussed in the first part of this chapter. The later section focuses on documentation of nerve block procedures, which is a natural accompaniment to the use of these empirical monitors. The proper documentation of how a nerve block was performed has obvious medicolegal implications and aids the future practitioner in choosing the best nerve block regimen for that particular patient.
What Are the Available Monitors?
Monitors, as used in the medical sense, are devices that assess a specific physiologic state and warn the clinician of impending harm. The monitors discussed in this chapter include nerve stimulation, ultrasonography, and the monitoring of injection pressure. Each of these has its own distinct set of both advantages and limitations. For this reason, these three technologies are best used in a complementary fashion (Figure 5-1), to minimize the potential for patient injury, rather than just relying on the information provided by one monitor alone. The combination of all three monitors is likely to produce the safest possible environment in which to perform a peripheral nerve block.
Three modes of monitoring peripheral nerve blocks for patient injury. The overlapping area of all three (yellow area) represents the safest means of performing a block.
A fourth monitor that many clinicians use regularly is the use of epinephrine in the local anesthetic. Good evidence supports this practice as a means of improving safety during peripheral nerve blocks, particularly in patients receiving higher doses of local anesthetic. First, it acts as a marker of intravascular absorption. About 10 to 15 μg of epinephrine injected intravenously reliably increases the systolic blood pressure >15 mm Hg, even in sedated or beta-blocked individuals (whereas a heart rate increase is ...