Ingeborg Schafhalter-Zoppoth

Ultrasound visibility of needles used for regional nerve block: An in vitro study

Background and objectives Ultrasound visibility of regional block needles is a critical component for safety and success of regional anesthetic procedures. The aim of the study was to formally assess factors that influence ultrasound visibility of needles used in regional anesthesia. Methods Regional block needles between 17- and 22-G diameter were inserted in a tissue equivalent phantom at angles from 0° to 65° relative to the phantom surface. For visibility enhancement, the needles were primed with air or water in combination with stylets and different size guide wires. Ultrasound measurements of needle tips and shafts were performed using transversal and longitudinal imaging with a linear 15-MHz transducer. Univariate and multivariate statistical analyses were performed on 719 visibility measurements. Results Hustead tip needles exhibited best ultrasound visibility. Ultrasound visibility of the needle tip was increased by insertion of a medium size guide wire. Water or air priming of the needle, insulation, and the insertion of a stylet did not influence needle visibility. Long axis imaging of the needle for shallow insertion angles (<30° in relation to the phantom surface) and short-axis imaging for steep angles (>60°) provided the best ultrasound visibility of the needle tips. Needle visibility decreased linearly with steeper insertion angles (P < .001) and smaller needle diameters (P < .001). Conclusions The results of our in-vitro study suggest a number of factors enhancing ultrasound visibility of regional block needles. The use of needles in the largest possible size inserted with a medium-size guide wire provides the best ultrasound visibility. Analysis of the approach angle favors needle insertion parallel to the transducer. The consideration of these factors may improve safety and success of ultrasound-guided regional blocks.

The Musculocutaneous Nerve: Ultrasound Appearance for Peripheral Nerve Block

Background and Objectives To gain complete anesthesia of the forearm, block of the musculocutaneous nerve is necessary. Variations in its course and position make localization of the musculocutaneous nerve problematic. The aim of the study is to describe the ultrasound appearance of the musculocutaneous nerve in the axilla and to suggest potential areas to target neural block. Methods We scanned the axillary regions of 19 volunteers and assessed the size and shape of 34 musculocutaneous nerves at entry into, exit from, and in the center of the coracobrachialis muscle. Furthermore, we measured the depth of the musculocutaneous nerve under the skin surface and its distance from the axillary artery at those 3 measurement points. Results As it travels through the coracobrachialis muscle, the musculocutaneous nerve changes in shape from oval to flat-oval to triangular. During this course, the musculocutaneous nerve also separates from the axillary artery and becomes more lateral while changing its depth from the surface. The musculocutaneous nerve increases its transverse area along this nerve path. In 2 subjects, the musculocutaneous nerve could not be visualized unilaterally within the course of the coracobrachialis muscle. Conclusions Knowledge of its ultrasound appearance facilitates localization and successful block of the musculocutaneous nerve. Because the distance between the musculocutaneous nerve and brachial plexus varies, different locations of musculocutaneous nerve puncture during ultrasound-guided regional anesthesia can be chosen.

sonographic Imaging of the Obturator Nerve for Regional Block

Background and Objectives: Today, there is a growing appreciation of the importance of the obturator nerve in clinical anesthesia. The aim of this study is to describe the ultrasound appearance of the obturator nerve for potential utility in guiding these nerve blocks. Methods: We scanned left and right inguinal regions of 20 volunteers lateral and distal to the pubic tubercle (PT) and assessed visibility, size and shape, and depth from the skin of common obturator nerves and their associated divisions. In addition to the volunteer study, we retrospectively reviewed a clinical series of obturator nerve blocks performed with ultrasound guidance and nerve stimulation. Results: The obturator nerve can be sonographically visualized by scanning along the known course of the nerve; the anterior division characteristically converges toward the posterior division along the lateral border of the adductor brevis muscle to form the common obturator nerve more proximally. In the set of 20 volunteers, 25% (10/40) of common, 85% (34/40) of anterior, and 87.5% (35/40) of posterior obturator nerves were sonographically identified. The common obturator nerve was visualized 1.3 ± 1.5 cm distal and 2.3 ± 1.2 cm lateral to the PT. Divisions were visualized 2.1 ± 2.0 cm distal and 2.1 ± 1.2 cm lateral to the PT. The nerves (common, anterior, and posterior) averaged 2.7 ± 1.2 mm, 1.4 ± 0.6 mm, and 1.7 ± 0.6 mm in anterior-posterior dimension and 9.0 ± 4.3 mm, 9.6 ± 3.9 mm, and 10.9 ± 4.1 mm in medial-lateral dimension and were 25.9 ± 7.6 mm, 15.5 ± 3.9 mm, and 29.3 ± 7.9 mm below the skin surface. The common obturator nerve and its anterior and posterior divisions are all relatively flat nerves with average anterior-posterior/medial-lateral dimension ratios of 0.32, 0.18, and 0.18, respectively. In the clinical series, nerve identification was confirmed with nerve stimulation (n = 6 block procedures, mean threshold stimulating current for evoked adductor contraction = 0.70 ± 0.14 mA). Conclusions: The obturator nerve and its divisions are the flattest peripheral nerves yet described with ultrasound imaging. Knowledge of the obturator nerves ultrasound appearance facilitates localization of this nerve for regional block and may increase success of such procedures.

Ultrasound guidance for ulnar nerve block in the forearm.

Objective The objective of this study was to establish the feasibility of ulnar nerve block under direct imaging. Case reports Two patients undergoing surgery on the fifth digit or medial hand received ulnar nerve blocks in the mid-forearm (approximately 15 cm proximal to the styloid process of the ulna). Ultrasound imaging was used to identify the ulnar nerve in the forearm and guide local anesthetic infiltration. Both patients had successful blocks, including sensory anesthesia of the dorsomedial hand. Conclusions Ultrasound guidance for ulnar nerve block in the forearm is a promising technique that includes block of the dorsal cutaneous branch. Anatomic and sonographic considerations are discussed.

The importance of transducer angle to ultrasound visibility of the femoral nerve.

To the Editor: Anisotropy is a property of muscles, nerves, and tendons that relates to the change in ultrasound appearance with the angle of insonation. This means that the amplitudes of their received echoes, hence image visibility, depend on the tilt angle of the scan head.1 This phenomenon occurs because of the presence of specular (“mirrorlike”) elements in anatomic structures. Although tendon anisotropy has been well studied,2,3 the extent to which peripheral nerves are anisotropic has not been quantitated. After receiving institutional review board approval and obtaining informed consent, we scanned the inguinal region of 12 healthy volunteers. The femoral nerve was visualized in short-axis view near the inguinal crease with the volunteers in the supine position and the transducer manipulated to obtain the brightest possible nerve image. Tilting the transducer 10° 4° caudally or 13° 5° cephalad (mean standard deviation) made the femoral nerve isoechoic with the adjacent iliopsoas muscle (Fig 1). Tendon anisotropy has been formally quantified by rotating ex vivo specimens in a water bath.2,3 These measurements have shown that angle changes as small as 2° to 3° from perpendicular can make tendon isoechoic to surrounding muscles.2,3 These changes in angle, although smaller, are similar to what we found in our in vivo clinical study of nerve anisotropy. Although some series have reported relatively consistent femoral nerve visibility,4,5 femoral nerve imaging can be challenging in some subjects. We postulate that some of the difficulty in visualization may relate to the high sensitivity of the femoral nerve imaging to the tilt angle of the transducer. Furthermore, with the in-plane technique, visualization of the block needle typically requires transducer manipulation. Therefore, simultaneous visualization of the block needle and nerve can be difficult. Sonographically guided blocks rely on clear visualization of peripheral nerves. It is therefore imperative that regional anesthesiologists be aware of all factors that influence peripheral nerve visibility. The anisotropic nature of peripheral nerves can aid clinicians in optimal visualization and promote the success and safety of invasive procedures guided by ultrasound.

Lateral popliteal nerve block with ultrasound guidance

1. Borene SC, Edwards JN, Boezaart AP. At the cords, the pinkie towards: Interpreting infraclavicular motor responses to neurostimulation. Reg Anesth Pain Med 2004;29:125-129. 2. Williams PL (ed). Gray’s Anatomy. Muscles and Fasciae of the Upper Limb (ed 38). New York, NY: Churchill Livingstone; 1995:835-862. 3. Wilbourn AJ. Brachial plexus disorders. In: Dyck PJ, Thomas PK, eds. Peripheral Neuropathy (ed 3). Philadelphia, PA: Saunders; 1993:911-950.

Ultrasound-guided ulnar nerve block in the presence of a superficial ulnar artery

To the Editor: Ultrasound imaging in regional anesthesia is evolving into an important adjunct. With rapid identification of anatomic structures, new techniques of ultrasoundguided regional blocks have become possible. Because vessels are easily identified with pulse-wave Doppler and conventional 2-dimensional imaging, they can serve as valuable landmarks to establishing regional block. In the forearm, the ulnar artery accompanies the ulnar nerve on its lateral side in over 90% of the general population. However, in some individuals, the ulnar artery runs superficial to the fascia covering the flexor muscles, a condition described as superficial ulnar artery, which has an incidence of 0.7% to 9.4%.1 To date, there is only 1 case report using Doppler ultrasound to visualize a superficial ulnar artery.2 Here we describe the performance of a successful ultrasound-guided ulnar nerve block in which a superficial ulnar artery was detected. A 24-year-old healthy man (76 kg) with fractures of the fourth and fifth metacarpal bones (boxer’s fractures) was scheduled for closed reduction and percutaneous pinning. The patient was intact neurovascularly but complained of pain (a verbal analog score of 3, where 0 no pain and 10 worst imaginable pain). After premedication with midazolam 2 mg intravenous (IV) and fentanyl 100 g IV, ultrasound imaging of the forearm revealed a superficial ulnar artery (Fig 1). Ultrasound-guided ulnar nerve block was performed in the mid-forearm using the in-plane technique, with the needle approaching the nerve from the medial to lateral aspect.3 A mixture of 10 mL of levobupivacaine 0.5% and buprenorphine 150 g was administered using a 23-gauge Quincke tip needle mounted on a 10-mL control syringe. General anesthesia was then induced with propofol 150 mg IV and maintained with sevoflurane via laryngeal mask airway. The surgery and anesthetic were uneventful. In the postanesthesia care unit, the patient reported no pain and had sensory block in the ulnar distribution. Two hours after ulnar nerve block, the patient was discharged home without complaints or additional medications. The ulnar nerve has an internal fascicular appearance characterized by hypoechoic fascicles surrounded by hyperechoic connective tissue (a “honeycomb” pattern). In the regular anatomy of the forearm, the ulnar nerve joins the ulnar artery between the flexor digitorum superficialis, flexor digitorum profundus, and flexor carpi ulnaris

Allergic contact dermatitis caused by ultrasonic gel.

To the Editor: Continuous epidural analgesia is commonly used for management of postoperative pain associated with totaljoint replacement surgeries. No controlled studies are available that define the risk of neuraxial bleeding associated with the use of an epidural catheter for postoperative analgesia with concomitant use of low-molecularweight heparin (LMWH). However, in March of 2002, a set of consensus guidelines was issued by ASRA regarding the concurrent use of LMWH and the performance of neuraxial anesthesia or the use of neuraxial catheters. We report a case of epidural hematoma formation associated with an epidural catheter placed for bilateral total-knee replacement surgery in a patient who was also receiving LMWH. An 80-year-old male presented for bilateral total-knee replacement surgery. After discussion of the options and the potential benefits and risks of various anesthetic techniques, the patient consented to proceed with an epidural technique for anesthesia and postoperative analgesia. The epidural catheter was placed by a CRNA with 23 years of experience. By use of sterile technique, an epidural catheter was placed at L2-3 without difficulty. Anesthesia was provided by administration of 0.5% bupivacaine into the epidural space, and the procedure was accomplished without apparent problems. After surgery, an epidural infusion of 0.2% ropivacaine with 2 g/mL of fentanyl was established in the recovery room, and the patient was transferred to the floor in stable condition. Upon arrival to the floor, he was given 15 mg of ketorolac and 2 mg of morphine intravenously for inadequate pain control. The following day, the infusion was switched to 0.1% ropivacaine, and exactly 20 hours after the placement of the epidural catheter, he was given a 40-mg injection of LMWH. The patient continued to complain of pain in his knees, which was not improved either with oral oxycodone and hydrocodone or by increasing the concentration of ropivacaine. A decision was made to discontinue the epidural infusion. The catheter was withdrawn 12 hours after the last dose of LMWH, and the subsequent dose was held until 4 hours thereafter. On the second postoperative day, the patient started to complain of back pain, which continued to get worse. Magnetic resonance imaging (MRI) of the lumbar spine showed an epidural hematoma extending from T-10 to L3. An urgent neurosurgical evaluation was sought, and the patient underwent laminectomy and evacuation of the epidural hematoma. The patient did not develop neurologic deficits and was discharged from the institution after a few days. He has received follow up in the orthopedic offices, and he continues to do well. This case illustrates how a patient being managed with an indwelling epidural catheter and receiving concomitant LMWH for DVT prophylaxis suffered a significant adverse complication. This event took place even though guidelines from the ASRA consensus statement were apparently followed as far as the time interval between catheter placement, withdrawal, and LMWH administration were concerned. The administration of ketorolac the previous day may have added to the risk, and we feel that this event must be reported to reiterate the risks of leaving indwelling catheters in place, with concomitant use of LMWH. We have discontinued the practice of using epidural analgesia concomitantly with LMWH in our institution and employ other modalities to provide analgesia to our patients.

Aspects of Femoral Nerve Block

elastic ribbon with markings of slightly less than 2 cm is used (Fig 2). By placing the zero line on one landmark and stretching the ribbon to another landmark the correct spacing of cun for that body region is defined. This length not only varies between different regions of the body but also accounts for the different body types and might serve as an alternative method of measurement than the one proposed by the authors. The article highlights the importance of individualizing anatomic measurements; however, cun is not a precise unit of measurement and as described adds to the confusion. Perhaps the authors should rename their unit of measurement something other than cun.

Reply to Drs. Baumgarten and Thompson

ikelihood of local anesthetic toxicity is virtually nil. One ight say that this technique represents incremental dosng in its finest form. We are unaware of any published ccurrence of local anesthetic toxicity with the fan techique. Informal discussions with physicians around the ountry have failed to find anyone familiar with any nstances of toxicity with the fan approach. In large individuals, axillary block can become more hallenging. The physician must determine the depth of he axillary artery to place the ring of local anesthetic. In hese situations, the depth should be confirmed either by nding the axillary artery or vein with the needle or by btaining a paresthesia. In morbidly obese individuals, he use of ultrasound or nerve stimulation can be very elpful.4 Ultrasound is surely a useful adjunct for difficult axilary blocks. With time, ultrasound guidance may become outine for some other peripheral nerve blocks.5 Allowng ultrasound proponents to force the issue by claiming hat ultrasound guidance is the only safe technique for all xillary blocks would be unfortunate.