Amaresh Vydyanathan

Ultrasound-guided Cervical Selective Nerve Root Block: A Fluoroscopy-controlled Feasibility Study

Background and Objectives: Reports of intravascular injection during cervical transforaminal injections, even after confirmation by contrast fluoroscopy, have led some to question the procedures safety. As ultrasound allows for visualization of soft tissues, nerves, and vessels, thus potentially improving precision and safety, we evaluated its feasibility in cervical nerve root injections. Methods: This is a prospective series of 10 patients who received cervical nerve root injections using ultrasound as the primary imaging tool, with fluoroscopic confirmation. Our radiologic target point was the posterior aspect of the intervertebral foramen just anterior to the superior articular process in the oblique view and at the midsagittal plane of the articular pillars in the anteroposterior (AP) view. Results: The needle was exactly at the target point in 5 patients in the oblique view and in 3 patients in the AP views. The needle was within 3 mm in all patients in the lateral oblique view and in 8 patients in the AP view. In the remaining 2 patients, the needle was within 5 mm from the radiologic target. In 4 patients, we were able to identify vessels at the anterior aspect of the foramen, whereas 2 patients had critical vessels at the posterior aspect of the foramen, and in 1 patient, this artery continued medially into the foramen, most likely forming or joining a segmental feeder artery. In both cases, the vessels might well have been in the pathway of a needle correctly positioned under fluoroscopic control. Conclusions: Our case series shows the feasibility of using ultrasound imaging to guide selective cervical nerve root injections. It may facilitate identifying critical vessels at unexpected locations relative to the intervertebral foramen and avoiding injury to such vessels, which is the leading cause of the reported complications from cervical nerve root injections. A randomized controlled trial to compare the effectiveness and safety of ultrasound imaging against other imaging techniques seems warranted.

Investigating the Efficacy of Dexmedetomidine as an Adjuvant to Local Anesthesia in Brachial Plexus Block: A Systematic Review and Meta-analysis of 18 Randomized Controlled Trials

Background and Objectives Dexmedetomidine has been thought to be an effective adjuvant to local anesthetics in brachial plexus blockade. We sought to clarify the uncertainty that still exists as to its true efficacy. Methods A meta-analysis of randomized controlled trials was conducted to assess the ability of dexmedetomidine to prolong the duration and hasten the onset of motor and sensory blockade when used as an adjuvant to local anesthesia for brachial plexus blockade versus using local anesthesia alone (control). A search strategy was created to identify eligible articles in MEDLINE, EMBASE, and The Cochrane Library. The methodological quality for each included study was evaluated using the Cochrane Tool for Risk of Bias. Results Eighteen randomized controlled trials were included in this meta-analysis (n = 1092 patients). The addition of dexmedetomidine significantly reduced sensory block time onset time by 3.19 minutes (95% confidence interval [CI], −4.60 to −1.78 minutes; I 2 = 95%; P < 0.00001), prolonged sensory block duration by 261.41 minutes (95% CI, 145.20–377.61 minutes; I 2 = 100%; P < 0.0001), reduced the onset of motor blockade by 2.92 minutes (95% CI, −4.37 to −1.46 minutes; I 2 = 96%, P < 0.0001), and prolonged motor block duration by 200.90 minutes (CI, 99.24–302.56 minutes; I 2 = 99%; P = 0.0001) as compared with control. Dexmedetomidine also significantly prolonged the duration of analgesia by 289.31 minutes (95% CI, 185.97–392.64 minutes; I 2 = 99%; P < 0.00001). Significantly more patients experienced intraoperative bradycardia with dexmedetomidine (risk difference [RD], 0.06; 95% CI, 0.00–0.11; I 2 = 72%; P = 0.03); however, there was no difference in the incidence of intraoperative hypotension (RD, 0.01; 95% CI, −0.02 to 0.04; I 2 = 3%; P = 0.45). It is important to note that all studies reported that intraoperative bradycardia was either transient in nature or reversible, when needed, with the administration of intravenous atropine. Conclusions Dexmedetomidine has the ability to hasten the onset and prolong the duration of blockade when used as an adjuvant to local anesthesia for brachial plexus blockade. Considering an analgesic effect to be either decreased pain, a longer duration of analgesic block, or decreased opioid consumption, the addition of dexmedetomidine to local anesthetics for brachial plexus blockade was found to significantly improve analgesia in all 18 included studies. However, patients receiving dexmedetomidine should be continuously monitored for the potentially harmful but reversible adverse effect of intraoperative bradycardia. Level of Evidence Therapeutic, level I.

The Anatomic Relationship of the Tibial Nerve to the Common Peroneal Nerve in the Popliteal Fossa: Implications for Selective Tibial Nerve Block in Total Knee Arthroplasty.

Background. A recently described selective tibial nerve block at the popliteal crease presents a viable alternative to sciatic nerve block for patients undergoing total knee arthroplasty. In this two-part investigation, we describe the effects of a tibial nerve block at the popliteal crease. Methods. In embalmed cadavers, after the ultrasound-guided dye injection the dissection revealed proximal spread of dye within the paraneural sheath. Consequentially, in the clinical study twenty patients scheduled for total knee arthroplasty received the ultrasound-guided selective tibial nerve block at the popliteal crease, which also resulted in proximal spread of local anesthetic. A sensorimotor exam was performed to monitor the effect on the peroneal nerve. Results. In the cadaver study, dye was observed to spread proximal in the paraneural sheath to reach the sciatic nerve. In the clinical observational study, local anesthetic was observed to spread a mean of 4.7 + 1.9 (SD) cm proximal to popliteal crease. A negative correlation was found between the excess spread of local anesthetic and bifurcation distance. Conclusions. There is significant proximal spread of local anesthetic following tibial nerve block at the popliteal crease with possibility of the undesirable motor blocks of the peroneal nerve.

The Use of Electrical Impedance to Identify Intraneural Needle Placement in Human Peripheral Nerves: A Study on Amputated Human Limbs.

BACKGROUND:Even as the use of peripheral nerve blockade in the perioperative setting is increasing, neural injury secondary to accidental intraneural injection remains a significant patient safety concern. Current modalities, including electrical stimulation and ultrasound imaging, still lack consistency and absolute reliability in both the detection and prevention of this complication. The measurement of electrical impedance (EI) could be an easy and valuable additional tool to detect intraneural needle placement. Our objectives in this study were to measure the change in EI with intraneural needle advancement in recently amputated human limbs. METHODS:The study was conducted within 45 minutes of amputation. The nerves that were studied were the sciatic nerve in the popliteal fossa in above-knee amputations or the tibial nerve below the calf in below-knee amputations. The amputated limb was placed on a tray and under ultrasound imaging guidance, an insulated peripheral block needle connected to a nerve stimulator was placed extraneurally and subsequently advanced intraneurally. The experiment was repeated on the same nerve after exposure by surgical dissection. The differences in impedance measurements between intraneural and extraneural needle placement were compared. RESULTS:In the below-knee amputated extremity (tibial nerve, n = 6) specimens based on the ultrasound methods, mean ± SD for ultrasound-guided intraneural impedance was 10 ± 2 k&OHgr; compared with an extraneural impedance of 6 ± 1.6 k&OHgr; (P = 0.005). The difference between intraneural and extraneural impedance after open dissection was also significant when we repeated the analysis based on the same specimens (P = 0.005). Similarly, in the above-the-knee amputated extremity (sciatic nerve, n = 5) specimens, mean intraneural impedance was 35.2 ± 7.9 k&OHgr; compared with an extraneural impedance of 25.2 ± 5.3 k&OHgr; (P = 0.037). The difference between intraneural and extraneural impedance obtained after open dissection was also significant when we repeated the analysis based on the same specimens (P = 0.0002). The impedance values were consistent and similar to those obtained after open dissection. CONCLUSIONS:There is no reliable “gold standard” to predict or prevent intraneural needle placement during peripheral nerve blockade. This small sample-sized study demonstrated that there is a change in EI with intraneural needle advancement. In clinical practice, measurement of the EI in conjunction with nerve stimulation may serve as another tool to use for identifying intraneural needle placement during peripheral nerve blockade.