Practical Concepts in the Monitoring of Injection Pressures During Peripheral Nerve Blocks

Multimodal Approach in Minimizing Transient Neurological Complications Following Single Shot Brachial Plexus Block: A Prospective Observational Study

PURPOSE

The aim of the study was to assess the benefit of a using multimodal approach, including injection pressure monitoring (IPM) and different techniques of nerve localization, with respect to complications following single-shot brachial plexus block (SSBPB).

METHODS

In this study, 238 adults (132 males and 106 females) undergoing upper-limb surgeries under peripheral nerve block (PNB) were evaluated. Of these, 198 patients were given supraclavicular block, and 40 patients received interscalene block using either ultrasound (USG) and peripheral nerve stimulation (PNS) or PNS alone. Injection pressure monitoring was used in 216 patients.

RESULTS

Transient neurological deficit (TND) was observed in six out of 198 patients where USG and NS were used along with IPM as opposed to 12 out of 18 patients without IPM (p<0.0001). In patients where only PNS was used, transient neurological deficit (TND) was seen in six out of 18 patients with IPM as opposed to all the patients (n=4) without IPM (p<0.02). Among the patients where injection pressure was monitored, six out of 198 patients developed TND when both USG and NS were used, compared to six out of 18 patients where only PNS was used (p<0.007).

CONCLUSION

Use of injection pressure monitoring along with different nerve localization techniques results in fewer transient neurological deficits.

Evaluation of the B-Smart manometer and the CompuFlo computerized injection pump technology for accurate needle-tip injection pressure measurement during peripheral nerve blockade

Background and Objectives

The exact mechanism of peripheral nerve blocks causing/leading to nerve injury remains controversial. Evidence from animal experiments suggests that intrafascicular injection resulting in high injection pressure has the potential to rupture nerve fascicles and may consequently cause permanent nerve injury and neurological deficits. The B-Smart (BS) in-line manometer and the CompuFlo (CF) computerized injection pump technology are two modalities used for monitoring pressure during regional anesthesia. This study sought to explore the accuracy of these two technologies in measuring needle-tip pressures in a simulated environment.

Methods

In seven simulated needle–syringe combinations, the BS and the CF devices were connected in series through a closed system and attached to a digital manometer at the tip of various needles. The pressures were evaluated in three trials per needle-syringe combination. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy (F1 Score) were determined for each needle type and overall.

Results

For pressures ≥15 psi and ≥20 psi, respectively, the CF device demonstrated a sensitivity of 100%, 100%; specificity of 96%, 98%; positive predictive value 93%, 93%; and negative predictive value of 100%, 100%. The BS device demonstrated a sensitivity of 60%, 100%; specificity of 99%, 95%; positive predictive value of 96%, 85%; and negative predictive value of 85%, 100%. Accuracy, as measured by the F1 Score, for detecting a pressure of ≥15 psi was 0.96 for the CF and 0.74 for the BS.

Conclusions

Future research is needed to explore in-vivo performance and evaluate whether either of these devices can impact on clinical outcomes.

The minimum effective concentration (MEC90 ) of ropivacaine for ultrasound-guided supraclavicular brachial plexus block

The aim of this study was to determine the minimum effective concentration of ropivacaine for ultrasound-guided supraclavicular brachial plexus block. Fifty-one patients undergoing arm surgery received double-injection ultrasound-guided supraclavicular block using ropivacaine 40 ml. The concentration of ropivacaine administered to each patient started at 0.225% and then depended on the response of the previous one, based on a biased coin design up-and-down sequential method. In case of failure, the ropivacaine concentration was increased by 0.025% w/v in the next subject. In the case of a successful block, the next patient was randomised to the same concentration or a concentration 0.025% w/v less. Success was defined as complete sensory blockade of the brachial plexus 30 min after the block together with pain-free surgery. The minimum effective ropivacaine concentration in 90% of subjects was 0.257% w/v (95% CI 0.241-0.280%).

Pathophysiology and Etiology of Nerve Injury Following Peripheral Nerve Blockade

This review synthesizes anatomical, anesthetic, surgical, and patient factors that may contribute to neurologic complications associated with peripheral nerve blockade. Peripheral nerves have anatomical features unique to a given location that may influence risk of injury. Peripheral nerve blockade-related peripheral nerve injury (PNI) is most severe with intrafascicular injection. Surgery and its associated requirements such as positioning and tourniquet have specific risks. Patients with preexisting neuropathy may be at an increased risk of postoperative neurologic dysfunction. Distinguishing potential causes of PNI require clinical assessment and investigation; a definitive diagnosis, however, is not always possible. Fortunately, most postoperative neurologic dysfunction appears to resolve with time, and the incidence of serious long-term nerve injury directly attributable to peripheral nerve blockade is relatively uncommon. Nonetheless, despite the use of ultrasound guidance, the risk of block-related PNI remains unchanged.

WHAT'S NEW

Since the 2008 Practice Advisory, new information has been published, furthering our understanding of the microanatomy of peripheral nerves, mechanisms of peripheral nerve injection injury, toxicity of local anesthetics, the etiology of and monitoring methods, and technologies that may decrease the risk of nerve block-related peripheral nerve injury.

Standard approaches for upper extremity nerve blocks with an emphasis on outpatient surgery

PURPOSE OF REVIEW

Currently, no standards exist with regard to the techniques and administration of ultrasound-guided peripheral nerve blocks. Consequently, the techniques and teaching substantially vary among practitioners and institutions. The purpose of this review is to propose a set of standard US-guided techniques for upper extremity nerve blocks.

RECENT FINDINGS

On the basis of the synthesis of information in available literature and the consensus of an internationally recognized collaborative panel of regional anaesthesia experts, the review recommends a standardized approach to common upper extremity nerve blocks using ultrasound guidance.

SUMMARY

A set of structured recommendations and approaches are suggested to help standardize clinical practice and teaching of ultrasound-guided upper extremity nerve blocks. Additional emphasis is placed on the discussion of nerve blocks in outpatient surgery.