The incidence of complications from general anesthesia has diminished substantially in recent decades, largely due to advances in monitoring of the respiratory and cardiovascular function during administration of anesthesia.1 The use of objective monitors such as pulse oximetry, capnography, electrocardiography, etc., allow practitioners to timely identify changing physiologic parameters, intervene rapidly and appropriately, and guide their therapeutic decisions.
The practice of regional anesthesia has traditionally suffered from a lack of objective monitors that aid the practitioner in more objectively monitoring the needle-nerve relationship and preventing neurologic injury. The practice of peripheral nerve blocks traditionally relied 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, practitioners can now monitor the interaction at the needle–fascial layers using ultrasonography. Likewise, quantifying the minimal current intensity and resistance to injection can be used to gather additional data useful in clinical decision-making to minimize the risk of needle placement into an unwanted tissue plane, intravascularly, or into vulnerable anatomical structures intraneurally. Recent advances in monitoring therefore may reduce 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 latter section focuses on documentation of nerve block procedures, which is logical record keeping of the objective information obtained by the monitors. Objective and robust documentation of how a nerve block was performed has obvious medicolegal implications and provides a useful database to guide advances in safety and efficacy.
Available Means for Monitoring Needle-Nerve Relationships
Monitors, as used in the medical practice, are devices that assess a specific physiologic state and warn the clinician of impending harm. The monitors discussed in this chapter include those for nerve stimulation, ultrasonography, and monitoring injection pressure. Each of these has its own distinct set of both advantages and limitations and each is best used in an additive, complementary fashion (Figure 63–1) to minimize the potential for patient injury, rather than just relying on the information provided by one monitor alone. There is sufficient evidence-based information that the combination of all three monitors is likely to produce the safest possible process during the practice of peripheral nerve blocks.
Three modes of monitoring peripheral nerve blocks for patient injury. The overlapping area of all three (blue area) represents the safest means of performing a block.
Another, pharmacologic monitor, that many clinicians utilize regularly is ...