Just like in patients having general anesthesia, the practice of regional anesthesia requires comprehensive, organized preoperative assessment, patient education, preparation. Likewise, monitoring, and documentation of respiratory and cardiovascular parameters during the administration of regional anesthesia (e.g., oximetry, capnography, electrocardiography) for safety and guidance in therapeutic decision-making. In regional anesthesia, several needle and injection monitoring systems have become available to decrease the risk of nerve injury, local anesthetic (LA) toxicity, and inadvertent needle injury to adjacent structures.
The first part of this chapter describes needle and injection monitoring and the rationale for their use. The latter section focuses on the documentation of nerve block procedures or medical record-keeping of the objective information obtained by the monitors. Objective and robust documentation of how a nerve block is performed provides useful database information to inform on the matters of safety and efficacy and may have medicolegal implications.
AVAILABLE MEANS FOR MONITORING NEEDLE-NERVE RELATIONSHIPS
Monitors, as used in medical practice, are devices that assess a specific physiologic state, provide objective data, allow for trending of the provided information, and can warn the clinician of impending harm. In this chapter, we discuss the currently available clinical monitors, such as ultrasonography, nerve stimulation, and injection pressure, and remark on some emerging technology. Each monitor has its advantages and limitations, and each can be used in an additive, complementary fashion (Figure 6-1) to minimize the potential for patient injury, rather than relying only on the information provided by a single monitor alone. Evidence-based information suggests that a combination of monitors is likely to enhance the safety of peripheral nerve blocks (PNBs).
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.
Epinephrine as a Monitor of Intravascular Injection
Some clinicians use epinephrine in the LA as a pharmacologic monitor to improve detection of an intravascular injection and contribute to the safety during PNBs. Intravenous injection of 10 to 15 μg epinephrine increases the systolic blood pressure more than 15 mmHg, even in premedicated patients or patients treated with β-blockers. This increase in blood pressure may help early detection of intravascular injection and prompt discontinuation of the injection. Epinephrine also decreases the absorption of the LA in perineural tissues or in local infiltration. This may decrease the peak plasma level of LA and lower the risk for systemic toxicity. Concerns regarding vasoconstriction and nerve ischemia with the addition of epinephrine have not been substantiated. Concentrations of 2.5 μg/mL (1:400,000) actually may increase intraneural blood flow due to the predominance of the β-effect of the drug in small doses. All in all, epinephrine may enhance safety during the ...