Guidance of block needle insertion by electrical nerve stimulation: a pilot study of the resulting distribution of injected solution in dogs

The role of peripheral nerve stimulation in the era of ultrasound-guided regional anaesthesia

With the widespread use of ultrasound for localising nerves during peripheral nerve blockade, the value of electrical nerve stimulation of evoked motor responses has been questioned. Studies continue to show that, compared with nerve stimulation, ultrasound guidance alone leads to: significantly improved block success; decreased need for rescue analgesia; decreased procedural pain; and lower rates of vascular puncture. Nerve stimulation combined with ultrasound does also not appear to improve block success rates, apart from those blocks where the nerves are challenging to view, such as the obturator nerve. The role of nerve stimulation has changed in the last 15 years from a technique to locate nerves to that of an adjunct to ultrasound. Nerve stimulation can serve as a monitor against needle-nerve contact and may be useful in avoiding nerves that are in the needle trajectory during specific ultrasound guided techniques. Nerve stimulation is also a useful adjunct in teaching novices ultrasound-guided regional anaesthesia, especially when the position and or appearance of nerves may be variable. In this review, the changing role of nerve stimulation in contemporary regional anaesthetic practice is presented and discussed.

Regional anaesthesia in patients with diabetes

Diabetes is the most common metabolic condition worldwide and about 20% of surgical patients will have this condition. It is a major risk-factor for worse outcomes after surgery including mortality; infective and non-infective complications; and increased length of stay. However, diabetes is a modifiable risk-factor, and programs to improve medical management have the potential to reduce peri-operative complications and the risk of harm. Regional anaesthesia has well-documented benefits in promoting the restoration of function but there are legitimate concerns that the incidence of complications of regional anaesthesia in patients with diabetes is higher. The aim of this review is to explore in detail the various potential advantages and disadvantages of regional anaesthesia in patients with diabetes. This, in turn, will allow practitioners to undertake more informed shared decision-making and potentially modify their anaesthetic technique for patients with diabetes.

Anterior humeral approach with nerve stimulator

INTRODUCTION

The prevalence of radial nerve injury during surgery is as high as the prevalence of radial nerve injury due to trauma. The aim of this study is to minimize the risk of iatrogenic injury of radial nerve.

MATERIALS AND METHODS

Fifty patients with middle or distal diaphysis fractures of humerus and 18 patients with pseudoarthrosis at the same localizations were treated with surgery. Plate-screw fixation was performed with anterior approach in 43 patients. Eleven patients had minimally invasive plate osteosynthesis, and 14 patients had intramedullary nailing. The localization of the radial nerve was determined with nerve stimulator at the area of dissection.

RESULTS

Iatrogenic radial nerve injury did not occur in patients treated with open reduction or minimally invasive approach.

DISCUSSION

Nerve stimulator may be a method that decreases radial nerve injury, an iatrogenic complication. This method may be used in anterior approach and minimally invasive procedures.

Pharmacodynamics and Pharmacokinetics of Lidocaine in a Rodent Model of Diabetic Neuropathy

Background

Clinical and experimental data show that peripheral nerve blocks last longer in the presence of diabetic neuropathy. This may occur because diabetic nerve fibers are more sensitive to local anesthetics or because the local anesthetic concentration decreases more slowly in the diabetic nerve. The aim of this study was to investigate both hypotheses in a rodent model of neuropathy secondary to type 2 diabetes.

Methods

We performed a series of sciatic nerve block experiments in 25 Zucker Diabetic Fatty rats aged 20 weeks with a neuropathy component confirmed by neurophysiology and control rats. We determined in vivo the minimum local anesthetic dose of lidocaine for sciatic nerve block. To investigate the pharmacokinetic hypothesis, we determined concentrations of radiolabeled (14C) lidocaine up to 90 min after administration. Last, dorsal root ganglia were excised for patch clamp measurements of sodium channel activity.

Results

First, in vivo minimum local anesthetic dose of lidocaine for sciatic nerve motor block was significantly lower in diabetic (0.9%) as compared to control rats (1.4%). Second, at 60 min after nerve block, intraneural lidocaine was higher in the diabetic animals. Third, single cell measurements showed a lower inhibitory concentration of lidocaine for blocking sodium currents in neuropathic as compared to control neurons.

Conclusions

We demonstrate increased sensitivity of the diabetic neuropathic nerve toward local anesthetics, and prolonged residence time of local anesthetics in the diabetic neuropathic nerve. In this rodent model of neuropathy, both pharmacodynamic and pharmacokinetic mechanisms contribute to prolonged nerve block duration.

Comparison of Ultrasound-Guided Axillary Brachial Plexus Block Properties in Diabetic and Nondiabetic Patients: A Prospective Observational Study

PURPOSE

Patients with diabetes mellitus (DM) type 2 may have subclinical peripheral nerve neuropathy. We performed this study to compare the differences in duration of axillary brachial plexus blocks in patients with type 2 DM and without DM (NODM). Our hypothesis was that the sensory block duration would be prolonged in patients with DM.

METHODS

A total of 71 patients who were scheduled for elective forearm and/or hand surgery were enrolled in this study. Before surgery, they received ultrasound-guided axillary brachial plexus blocks with a mixture of 10 mL lidocaine 2% and 20 mL bupivacaine 0.5%. After surgery, all patients received 1 g paracetamol every 6 hours as needed. The primary end point was sensory block duration. Secondary end points were motor block duration, time until first pain (numeric rating scale [NRS] 4 or greater), highest NRS pain scores, and rescue analgesic consumption (NRS 4 or greater) through the first 2 postoperative days.

RESULTS

In all, 67 patients completed the study: 22 in the DM group and 45 in the NODM group. Sensory and motor block durations were longer in the DM group than in the NODM group (mean [range], 773.5 [479-1155] vs 375 [113-900] minutes, and 523 [205-955] vs 300 [110-680] minutes). Time until first pain was 855 (590-1,285) minutes in the DM group and 500 (200-990) minutes in the NODM group. The highest NRS scores were also significantly lower in the DM group at 6 and 12 hours. Paracetamol consumption was lower in the DM group through the first 2 postoperative days.

CONCLUSIONS

The presence of DM was associated with longer duration of the sensory block after axillary brachial plexus block.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic II.

Diabetic neuropathy increases stimulation threshold during popliteal sciatic nerve block

BACKGROUND

Peripheral nerve stimulation is commonly used for nerve localization in regional anaesthesia, but recommended stimulation currents of 0.3-0.5 mA do not reliably produce motor activity in the absence of intraneural needle placement. As this may be particularly true in patients with diabetic neuropathy, we examined the stimulation threshold in patients with and without diabetes.

METHODS

Preoperative evaluation included a neurological exam and electroneurography. During ultrasound-guided popliteal sciatic nerve block, we measured the current required to produce motor activity for the tibial and common peroneal nerve in diabetic and non-diabetic patients. Proximity to the nerve was evaluated post-hoc using ultrasound imaging.

RESULTS

Average stimulation currents did not differ between diabetic (n=55) and non-diabetic patients (n=52). Although the planned number of patients was not reached, the power goal for the mean stimulation current was met. Subjects with diminished pressure perception showed increased thresholds for the common peroneal nerve (median 1.30 vs. 0.57 mA in subjects with normal perception, P=0.042), as did subjects with decreased pain sensation (1.60 vs. 0.50 mA in subjects with normal sensation, P=0.038). Slowed ulnar nerve conduction velocity predicted elevated mean stimulation current (r=-0.35, P=0.002). Finally, 15 diabetic patients required more than 0.5 mA to evoke a motor response, despite intraneural needle placement (n=4), or required currents ≥2 mA despite needle-nerve contact, vs three such patients (1 intraneural, 2 with ≥2 mA) among non-diabetic patients (P=0.003).

CONCLUSIONS

These findings suggest that stimulation thresholds of 0.3-0.5 mA may not reliably determine close needle-nerve contact during popliteal sciatic nerve block, particularly in patients with diabetic neuropathy.

CLINICAL TRIAL REGISTRATION

NCT01488474.

[Localization of peripheral nerves. Success and safety with electrical nerve stimulation]

Peripheral electrical nerve stimulation is one of the standard applications in peripheral regional anesthesia in addition to the ultrasound technique. Among other findings, the visualization of needle and nerve during ultrasound-guided blockade caused a change in clinical practice of peripheral nerve stimulation in the last decade. In the present article old and new aspects of principles and clinical practice of the nerve stimulation technique are presented and summarized in a total clinical concept in order to achieve safe and successful peripheral regional anesthesia using electrical peripheral nerve stimulation.

Ultrasound-guided dorsal approach for femoral nerve blockade in cats: an imaging study

This study was conducted to describe and validate a dorsal ultrasound-guided approach to block the femoral nerve (FN) in cats by means of anatomical and computed tomography (CT) studies. The anatomical study was carried out in four fresh feline cadavers to determine the anatomic landmarks to approach this nerve. Then, an ultrasonographic study of the FN was performed in another eight cadavers using a 13 MHz linear transducer. The accuracy of the neurolocation by ultrasonography (US) was determined in four cadavers by the injection of 1 ml blue ink around the FN. The staining of the nerve was evaluated in anatomical studies. The feasibility of this technique was also evaluated by CT after injecting 1 ml of an iodinated contrast medium (150 mgl/ml) around the FN in the other four cadavers. The landmarks to approach the FN were the cranial border of the iliac crest and the dorsal processes of L6 and L7. The FN was visualised as a round hypoechogenic structure surrounded by a hyperechogenic rim located within the iliopsoas muscle on transverse scans. The anatomical and CT studies confirmed the accuracy of the US location of the FN. The dorsal ultrasound-guided approach may allow feasible and accurate access to the FN in cats and it could be useful in producing successful blockade.

Relationship between glycosylated hemoglobin level and sciatic nerve block performance in diabetic patients

BACKGROUND

The objective of the present study was to explore the effects of deficiencies in glucose regulation on the onset, regression, and block performance times in a group of patients with diabetes-related foot problems.

METHODS

Forty-eight patients with American Society of Anesthetists physical status 2-4 undergoing foot and ankle surgery with a popliteal fossa block were prospectively studied. Patients were stratified into cohorts based on 3 groups according to their HbA1c levels: group 1 (n = 15), HbA1c 5%-6%; group 2 (n = 16), HbA1c 7%-8%; group 3 (n = 17), HbA1c 9%-10%. A standardized local anesthetic mixture containing 10 mL of 2% prilocaine and 10 mL of 0.5% levobupivacaine was used in all study groups. The primary outcome of the study was the time for regression of the sensory block.

RESULTS

The onset times of sensory and motor blocks in group 3 were significantly longer than those in groups 2 and 1. Motor block regression time differed significantly between groups (P = .04), being longer in group 3 compared with group 1. In group 3, the sensory block regression time and the time of first analgesic use were significantly longer than the times in groups 1 and 2.

CONCLUSIONS

We found that sensory block regression time was longer in diabetic patients with poor glycemic control than in the patients with better glycemic control. Longer block performance time, probably due to reduction in sensory and motor conduction velocity in diabetic patients with poor glycemic control, should be taken into consideration when peripheral nerve blocks are used.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

The role of continuous peripheral nerve blocks

A continuous peripheral nerve block (cPNB) is provided in the hospital and ambulatory setting. The most common use of CPNBs is in the peri- and postoperative period but different indications have been described like the treatment of chronic pain such as cancer-induced pain, complex regional pain syndrome or phantom limb pain. The documented benefits strongly depend on the analgesia quality and include decreasing baseline/dynamic pain, reducing additional analgesic requirements, decrease of postoperative joint inflammation and inflammatory markers, sleep disturbances and opioid-related side effects, increase of patient satisfaction and ambulation/functioning improvement, an accelerated resumption of passive joint range-of-motion, reducing time until discharge readiness, decrease in blood loss/blood transfusions, potential reduction of the incidence of postsurgical chronic pain and reduction of costs. Evidence deriving from randomized controlled trials suggests that in some situations there are also prolonged benefits of regional anesthesia after catheter removal in addition to the immediate postoperative effects. Unfortunately, there are only few data demonstrating benefits after catheter removal and the evidence of medium- or long-term improvements in health-related quality of life measures is still lacking. This review will give an overview of the advantages and adverse effects of cPNBs.

Peripheral nerve stimulation in regional anesthesia

Peripheral nerve stimulation has a long history in regional anesthesia. Despite the advent of ultrasound-guided peripheral nerve blockade, nerve stimulation remains a popular technique used alone or, now, in combination with ultrasound-guided techniques. In light of this evolving utility of nerve stimulation, this is an appropriate time to review the basic concepts and knowledge base of this historically important tool. Electrical nerve stimulation facilitates nerve localization, using threshold current as a surrogate for needle-to-nerve distance. Preferential activation of motor nerves is possible because motor nerve fibers are more readily activated with a shorter duration of current compared with sensory nerves. The association between current and needle-to-nerve distance predicts that less current is needed to evoke a motor response as the needle moves closer to the nerve. Thus, an elicited motor response at or below 0.5 mA is considered a common end point for successful neural blockade. However, current magnitude is neither 100% sensitive nor specific. Independent of technical ability, both the biological environment and the equipment used impact the current-distance relationship. Thus, successful electrical nerve stimulation is dependent on an anesthesiologist with a solid foundation in anatomy and a thorough understanding of electrophysiology.

Ambulatory anesthesia and regional catheters: when and how

Several clinical trials have demonstrated the superiority of continuous peripheral nerve block compared with traditional opioid-based analgesia. The ability to provide safe and effective continuous peripheral nerve block at home is an attractive alternative to opioid-based analgesia with its related side effects. In this article, the practical issues related to catheter use in the ambulatory setting are discussed. Techniques for catheter placement, infusion regimens, patient education, and complications are subject to many institutional preferences. In this review, special emphasis is placed on evidence-based techniques.

Intraneural injection during nerve stimulator-guided sciatic nerve block at the popliteal fossa

BACKGROUND

Exact location of the needle tip during nerve stimulation-guided peripheral nerve blocks is unknown. Using high-frequency ultrasound imaging, we tested the hypothesis that intraneural injection is common with nerve stimulator-guided sciatic nerve (SN) block in popliteal fossa.

METHODS

Forty-two patients scheduled for hallux valgus repair were studied. Sciatic block at the popliteal fossa was accomplished using nerve stimulation. When a motor response was elicited at <0.5 mA (2 Hz, 0.1 ms), 40 ml of local anaesthetic (LA) was injected. Using ultrasound (Titan, Sonosite, 5-10 MHz), the diameters and area of the SN were measured before and after the injection. The presence of nerve swelling and proximal or distal diffusion of LA were also assessed. Intraneural injection was defined as nerve area (NA) increase of > OR =15% and one or more additional ultrasonographic markers (nerve swelling, proximal-distal diffusion within epineural tissue). Clinical neurological evaluation was performed 1 week after the block.

RESULTS

Post-injection NA increase > OR =15% was seen in 32 (76%) patients [0.54 (SD 0.19) cm(-2) vs 0.76 (0.24) cm(-2); P<0.05]. Nerve swelling with fascicular separation was observed in 37 (88%) patients; proximal and distal diffusion of LA were present in six (14%) and 14 (38%) patients, respectively. Intraneural injection criteria were met in 28 (66%) patients. Greater NA increase was present in patients with fast block onset [61 (45) vs 25 (33)%; (Dif 35% 95% CI 61-9%); P<0.05]. No patient developed neurological complications.

CONCLUSIONS

Intraneural (subepineural) injection is a common occurrence after nerve stimulator-guided SN block at the popliteal fossa, yet it may not inevitably lead to neurological complications.

Ultrasound guidance in regional anesthesia: state of the art review through challenging clinical scenarios

Ultrasound guided regional anesthesia (UGRA) for peripheral nerve blockade is becoming increasingly popular. The advantage of ultrasound technology is that it affords the anesthesiologist the real time ability to visualize neural structures, needle advancement, and local anesthetic spread. Recent data suggest that UGRA generates improved success rates and reductions in performance times in comparison to traditional approaches. Further, the use of ultrasound technology in peripheral nerve blocks has provided insight into needle-nerve interactions, revealing distinct limitations of nerve stimulator techniques. Given that UGRA requires a unique set of skills, formal standards and guidelines are currently being developed by leadership societies in order to foster education and training. This review article, in a case vignette format, highlights important techniques, concepts, and limitations regarding the use of ultrasound to facilitate regional anesthesia. Clinically relevant aspects of ultrasound physics are also discussed.