Successful interscalene block with a nerve stimulator may also result after a pectoralis major motor response

BACKGROUND AND OBJECTIVES: Interscalene block of the brachial plexus is a well-established anesthetic and analgesia technique for shoulder surgery. The endpoint for successful block using the nerve stimulator has been described by previous authors as a bicep motor response (twitch) and recently by a deltoid motor response. This retrospective observational case study of regular clinical practice examined the efficacy of using the pectoralis major motor response as an endpoint for a successful block. METHODS: A total of 120 patients who were scheduled for elective ambulatory shoulder surgery were retrospectively studied. All interscalene blocks were performed with aid of a nerve stimulator. Patients were categorized into 3 groups of 40 patients. Group 1 (biceps twitch), group 2 (deltoid twitch), and group 3 (pectoralis major twitch) were compared on success of the block. This retrospective study was conducted by reviewing interscalene block data sheets from the last 40 patients consecutively receiving interscalene block from either a bicep, deltoid, or pectoralis major motor response. A successful block was defined by the inability of the patient to raise their arm against gravity 20 minutes after injection of the local anesthetic. RESULTS: Pectoralis major motor response as an endpoint for local anesthetic injection was examined. Of 40 patients studied in this group, 38/40 were judged successful. This was comparable to the success rate in biceps (38/40 successful) and deltoid groups (37/40 successful). CONCLUSIONS: This retrospective observational case study of regular clinical practice suggests that a pectoralis major motor response can be a satisfactory endpoint for interscalene block.     

三角肌运动反应用于小儿经肌间沟臂丛神经阻滞的临床观察

目的为三角肌运动反应作为在外周神经刺激器定位下小儿经肌间沟臂丛神经阻滞终点的临床应用提供参考。方法60例拟行上肢手术患儿,在外周神经刺激器定位下行经肌间沟臂丛神经阻滞,随机分为3组:A组(20例),三角肌运动反应终点组;B组(20例),肱二头肌运动反应终点组;C组(20例),三角肌和肱二头肌运动反应终点组。比较各组在刺激域电流、获得终点时间、合作患儿运动阻滞起效时间及神经阻滞效果的差异。结果组间刺激域电流、运动阻滞起效时间、神经阻滞效果差异无统计学意义(P>0.05);A、B组获得终点时间大于C组(P<0.05)。结论三角肌运动反应终点可以作为小儿经肌间沟臂丛神经阻滞穿刺针正确定位的标志。     

成人肌间沟臂丛神经阻滞运动反应终点的研究

目的研究胸大肌、三角肌运动反应作为外周神经刺激器(PNS)定位下成人经肌间沟臂丛神经阻滞终点的可行性。方法择期成人上肢手术240例,PNS定位下行经肌间沟臂丛神经阻滞,随机均分为四组:胸大肌运动反应终点组(A组)、三角肌运动反应终点组(B组)、肱二头肌运动反应终点组(C组)和胸大肌、三角肌或肱二头肌运动反应终点组(D组)。比较组间刺激域电流、获得终点时间、运动阻滞起效时间、各神经分支感觉阻滞起效时间、运动阻滞效果、各神经分支感觉阻滞效果及神经阻滞综合效果。结果D组获得终点时间短于A、B、C组(P<0.05),组间刺激域电流、运动阻滞起效时间、各神经分支感觉阻滞起效时间、运动阻滞效果、各神经分支感觉阻滞效果及神经阻滞综合效果差异无统计学意义。神经阻滞综合优良率90.8%。结论胸大肌、三角肌运动反应终点可作为PNS定位下成人经肌间沟臂丛神经阻滞穿刺针正确定位的满意、安全标志。     

Spread of local anesthetic during an ultrasound‐guided interscalene block: does the injection site influence diffusion?

Background: During interscalene block (ISB) placement, ultrasound guidance (USG) enables the practitioner to measure the spread of local anesthetic around the nerve trunks or roots, and to adjust the needle position in order to optimize diffusion. Moreover, USG helps determine the best injection level, i.e. the point from which diffusion gives the most complete brachial plexus block. The aim of this study was to compare C5 and C6 level injections and to determine which level allows the best diffusion. Methods: Sixty randomized patients scheduled for shoulder surgery were divided into two groups. In group C5, injection was directed toward C5 while in group C6, the C6 nerve root was targeted. Block performance time was recorded. The onset of motor and sensory block of each nerve distribution was evaluated every 10 min over a 30‐min period. Results: The average time taken to perform a nerve block was 6.2+2.6 min in Group C6 and 6.0+2.1 min in Group C5 (NS). At 30 min, the number of patients with a satisfactory musculocutaneous and axillary nerve block was not notably greater in either group. By contrast, a significantly higher success rate was observed for other nerves in the C6 group as compared to the C5 group: ulnar nerve block: 93% vs. 19%, radial nerve block: 96% vs. 28%, median nerve block: 96%, vs. 69%. Conclusions: During USG ISB placement, injection below the C6 level provided the same efficiency in analgesia after shoulder surgery as an injection cranial to the C5 nerve root but a greater success rate of anesthesia in all distal nerve areas. This technique could be very interesting for trauma cases as an alternative to a supraclavicular block and offers a high success rate and is simple to perform, potentially promoting wide use and quicker learning for beginners.     

Ultrasound-guided block of the axillary nerve: a volunteer study of a new method

Background: Interscalene brachial plexus block (IBPB) is the gold standard for perioperative pain management in shoulder surgery. However, a more distal technique would be desirable to avoid the side effects and potential serious complications of IBPB. Therefore, the aim of the present study was to develop and describe a new method to perform an ultrasound‐guided specific axillary nerve block. Methods: After initial investigations, 12 healthy volunteers were included. We performed an in‐line ultrasound‐guided specific axillary nerve block by injecting 8 ml local anesthetic (lidocaine 20 mg/ml) after placing the tip of a nerve stimulation needle cranial to the posterior circumflex humeral artery in the neurovascular space bordered by the teres minor muscle, the deltoid muscle, the triceps muscle and the shaft of the humerus. Needle placement was aided by simultaneous nerve stimulation. We assessed sensory (pinprick and cold stimulation) and motor (active resistive force) block of the axillary nerve before, 15, 30, 60, 90 and 120 min after performing the block and every 30 min until termination of the block. Results: All 12 volunteers demonstrated sensory block of the axillary nerve and 10 volunteers demonstrated complete motor block. Even though it was difficult to directly visualize the axillary nerve, the block was easy to perform with easily recognizable ultrasonographic landmarks. Block duration was approximately 120 min. Conclusions: We describe a new ultrasound‐guided technique to specifically block the axillary nerve. The potential clinical role of this new block remains to be determined.     

Evaluation of a new fenestrated needle for ultrasound-guided fascia iliaca block

STUDY OBJECTIVE: To evaluate a new 20-gauge (G) fenestrated needle designed to be used with ultrasound guidance to deliver local anesthetic into the tissue plane of the fascia iliaca without immediate proximity to the femoral nerve. DESIGN: Prospective study. SETTING: University hospital. PATIENTS: 15 male volunteers. INTERVENTIONS: To determine the onset of motor and sensory block after ultrasound-guided injection of 1% lidocaine and iopamidol, fluoroscopy was performed during and after injection to discover the pattern of local anesthetic distribution. The buckling strength of the new needle was compared using a standard mechanical testing protocol to a conventional 22-G needle (Quincke type). MEASUREMENTS AND MAIN RESULTS: Injection through the fenestrated needle consistently produced sensory block in the anterior, medial, and lateral aspects of the thigh. All subjects were also observed to have loss of motor function in the quadriceps muscle. No subject experienced motor effect in the adductor muscles of the thigh. The fenestrated 20-G needle yielded at significantly larger compressive forces than did the standard 22-G needle (P < 0.001). CONCLUSION: The needle is novel in that it does not require immediate proximity to the femoral nerve or precise placement of the needle tip in the plane of the fascia iliaca. The 20-G fenestrated needle is stronger under compressive force than existing 22-G needles.     

Ultrasound-guided musculocutaneous nerve block: a description of a novel technique

BACKGROUND AND OBJECTIVE: Localizing the musculocutaneous nerve for neural blockade is crucial to providing surgical anesthesia for the distal forearm. We present a novel approach for localizing and anesthetizing the musculocutaneous nerve. CASE REPORTS: Ten patients underwent successful ultrasound-guided musculocutaneous nerve blocks. In this technique, either a 10-MHz or a 12-MHz linear probe was placed at the junction of the pectoralis major muscle and the biceps muscle such that the axillary artery was visualized in cross section. The probe was moved towards the biceps muscle until the musculocutaneous nerve was visualized lying between the coracobrachialis and biceps muscles. A 22-gauge, 50-mm b-bevel needle was inserted under direct vision until the needle was adjacent to the nerve. Local anesthetic was then injected, which generated surgical anesthetic conditions in all patients. CONCLUSION: Ultrasound can facilitate the localization and local anesthetic block of the musculocutaneous nerve.     

Applying ultrasound imaging to interscalene brachial plexus block

OBJECTIVE: Previous studies have examined ultrasound-assisted brachial plexus blocks, but few have applied this imaging technology to the interscalene region. We report a case of interscalene brachial plexus block using ultrasound guidance to show the clinical usefulness of this technology. CASE REPORT: A nerve stimulator-guided interscalene block was attempted for arthroscopic shoulder surgery but failed. Subsequent nerve localization was accomplished by ultrasound imaging using a high-frequency probe (5-12 MHz) and the Philips ATL HDI 5000 unit. Ultrasound showed nerves between the scalene muscles, block needle movement at the time of advancement, and local anesthetic spread during injection. Interscalene block was successful after 1 attempt of nerve localization and needle placement. CONCLUSIONS: Advanced ultrasound technology is useful for nerve localization and can generate brachial plexus images of high resolution in the interscalene groove, guide block needle placement and advancement in real time to targeted nerves, and assess adequacy of local anesthetic spread at the time of injection. Ultrasound imaging guidance can potentially improve success during interscalene brachial plexus block.     

Interscalene block anesthesia at an ambulatory surgery center performing predominantly regional anesthesia: a prospective study of one hundred thirty-three patients undergoing shoulder surgery

Interscalene block (ISB) of the brachial plexus is frequently used for patients undergoing ambulatory shoulder surgery. We previously reported that the incidence of postoperative complaints (neurapraxia) after an ISB was low (3% at 2 weeks), but objective neurologic assessment was not included in the study. The present study combines subjective findings with both preoperative and postoperative objective sensory and motor assessments after an ISB. We prospectively evaluated 133 patients undergoing elective ambulatory shoulder surgery. ISB anesthesia was accomplished by use of 1.5% mepivacaine alone or in combination with bupivacaine (0.5%-0.75%) via a paresthesia technique and a 23-gauge needle. All of the blocks were performed by experienced anesthesiologists. The number of passes with the needle, site of paresthesia, ease of performing the block, and success of the ISB were recorded for each patient. Neurologic assessment was performed preoperatively and up to 2 weeks postoperatively by 1 of 4 health care professionals but not by the anesthesiologists who performed the ISB and included diminished sensation, localized nerve pain, Semmes-Weinstein monofilament pressure threshold sensibility, Weber static 2-point discrimination, and grip strength changes. Patients with postoperative changes were followed up until resolution of symptoms occurred. Successful surgical anesthesia was achieved in 98% of the patients. There was 1 major perioperative complication (0.7%), a seizure that occurred within 5 minutes of the ISB. Two (1.4%) complained of transient postoperative neurapraxias. Neither patient had any changes in objective sensory and motor measurements. Hence, there was no correlation between subjective complaints and objective findings in this study. This study demonstrates that, in the hands of anesthesiologists doing predominantly regional anesthesia, there is a 1.4% incidence of neurologic complications after an ISB. ISB is a safe and effective technique for patients undergoing ambulatory shoulder surgery when an anesthesiologist experienced with regional anesthesia is involved.     

Suprascapular nerve block prolongs analgesia after nonarthroscopic shoulder surgery but does not improve outcome

Suprascapular nerve block (SSNB) reportedly improves analgesia and 24-h outcomes after arthroscopic shoulder surgery performed under general anesthesia. In this study, we assessed the analgesic and clinical outcome efficacy of SSNB as an adjunct to interscalene brachial plexus block (ISB) for ambulatory nonarthroscopic shoulder surgery. Fifty patients were randomized to receive either a SSNB or sham injection as part of a standardized ISB-general anesthesia regimen. Time to first significant pain (the primary outcome measure) was significantly delayed in the SSNB group (594 +/- 369 min versus 375 +/- 273 min, respectively; P = 0.02). There were no other differences between groups with regard to postanesthesia recovery unit measures, 24-h assessment of pain, supplemental analgesic use, or quality of life outcomes. We conclude that adjunctive SSNB adds minimal value to a primary ISB anesthetic for nonarthroscopic shoulder surgery. IMPLICATIONS: When used as an adjunct to an interscalene block combined with general anesthesia, suprascapular nerve block with bupivacaine moderately prolongs analgesia without improving other outcome measures after ambulatory nonarthroscopic shoulder surgery.     

A low approach to interscalene brachial plexus block results in more distal spread of sensory-motor coverage compared to the conventional approach

A low approach to the interscalene block (LISB) deposits local anesthetic farther caudad on the brachial plexus compared with the conventional interscalene block (ISB). We compared the efficacy of LISB and ISB in achieving anesthesia of the distal extremity in 254 patients having upper extremity surgery. The most frequent elicited motor response was the deltoid for ISB and wrist for LISB. There was significantly greater sensory-motor block of regions below the elbow with the LISB compared with ISB (P < 0.001 for both sensory and motor coverage). Our data indicate that LISB results in a higher incidence of distal elicited motor response and greater sensory-motor blockage of the wrist and hand.     

运动反应阈电流强于或弱于0．5mA在超声引导下行肌问沟神经阻滞均可产生良好效果

背景对超声引导下行肌间沟阻滞时神经电刺激的运动反应进行定量，并比较运动反应阈电流强于或弱于0．5mA时的阻滞情况。方法选择61例在肌间沟阻滞和全身麻醉下行非住院肩部手术的患者，进行前瞻性观察研究。手术前超声引导下在肌问沟放置一绝缘穿刺针，测定能诱发运动反应的最小电流值，并注射含肾上腺素的0．5％布比卡因30ml。测定上干（uppertrunk）支配区感觉和运动神经阻滞情况15分钟，然后开始全麻诱导。手术后记录麻醉后恢复室（PACU）中上干阻滞成功率和疼痛评分，并记录阻滞持续时间和手术后当晚镇痛药使用剂量。诱发运动反应的电流阈值≤0．5mA者编入A组，〉0．5mA者编入B组，并比较2组上述指标间的差异。结果诱发运动反应的电流阂值范围在0．14～1．7mA间，其中≤0．5mA者即A组病例占42％。所有患者均获得满意的上千感觉和运动阻滞，并且在PACU中无一例患者需要应用阿片类药物。两组的平均阻滞时问为17．8±4．9小时，手术后镇痛药物用量无差异。两组感觉阻滞起效时间相同，但15分钟时运动神经阻滞不全率B组（37％）高于A组（12％）（P=0．03）。结论超声引导下使用神经刺激仪行肌间沟神经阻滞时，出现运动反应的电流强度大于或小于Q5InA对上干阻滞成功率和持续时间无影响。     

Nerve puncture and apparent intraneural injection during ultrasound-guided axillary block does not invariably result in neurologic injury

BACKGROUND: Nerve puncture by the block needle and intraneural injection of local anesthetic are thought to be major risk factors leading to neurologic injury after peripheral nerve blocks. In this study, the author sought to determine the needle-nerve relation and location of the injectate during ultrasound-guided axillary plexus block. METHODS: Using ultrasound-guided axillary plexus block (10-MHz linear transducer, SonoSite, Bothel, WA; 22-gauge B-bevel needle, Becton Dickinson, Franklin Parks, NJ), the incidence of apparent nerve puncture and intraneural injection of local anesthetic was prospectively studied in 26 patients. To determine the onset, success rate, and any residual neurologic deficit, qualitative sensory and quantitative motor testing were performed before and 5 and 20 min after block placement. At a follow-up 6 months after the blocks, the patients were examined for any neurologic deficit. RESULTS: Twenty-two of 26 patients had nerve puncture of at least one nerve, and 21 of 26 patients had intraneural injection of at least one nerve. In the entire cohort, 72 of a total of 104 nerves had intraneural injection. Sensory and motor testing before and 6 months after the nerve injections were unchanged. CONCLUSIONS: Under the conditions of this study, puncturing of the peripheral nerves and apparent intraneural injection during axillary plexus block did not lead to a neurologic injury.     

The influence of interscalene block technique on adverse hemodynamic events

Purpose

A hemodynamic event such as hypertension after interscalene block (ISB) is a complication that is often overlooked. The irregular spread of local anesthetic would cause a blockade of carotid sinus baroreceptors leading to the adverse event. The purpose of the present study is to compare ultrasound and neurostimulation technique in preventing hypertension after ISB.

Methods

Thirty patients without hypertension history who underwent arthroscopic shoulder surgery for a rotator cuff tear were enrolled. After preoperative administration of the State Trait Anxiety Inventory questionnaire, patients were allocated to receive ultrasound-guided ISB with 20 ml levobupivacaine-HCl 0.5 % (group US) and 40 ml levobupivacaine-HCl 0.5 % with neurostimulation (group NS). The need for antihypertensive drug was recorded. Block onset sensory and motor times were assessed. Systolic and diastolic blood pressures, and heart rate and pulse oximetry (SpO₂), were evaluated before the block as well as 2, 5, 10, 15, 20, and 30 min after.

Results

No differences in patient characteristics and anxiety were found in the two groups. Block onset times were similar. At 15 min after block placement, group NS showed significantly higher systolic and diastolic blood pressures compared to group US. No differences in heart rate and SpO₂ were found between the two groups. Three patients of group NS required urapidil administration because of hypertension.

Conclusions

Ultrasound-guided ISB permits the use of a low volume of local anesthetic and seems to reduce the incidence of hypertension.     

Phrenic nerve block caused by interscalene brachial plexus block: effects of digital pressure and a low volume of local anesthetic.

BACKGROUND AND OBJECTIVES: Interscalene brachial plexus block (ISB) is associated with phrenic block and diaphragmatic paralysis when high volumes (40-50 mL) of local anesthetic are injected. The goal of our study was to test if a low volume of local anesthetic administered while maintaining proximal digital pressure might more selectively block the brachial plexus and decrease the frequency of phrenic nerve block. METHODS: Twenty healthy patients undergoing ISB for orthopedic surgery of the upper extremity were randomly allocated to receive either 20 mL 1.5% mepivacaine while proximal digital pressure to the site of puncture was performed, or 40 mL 1.5% mepivacaine without digital pressure. Spirometry and clinical data were evaluated at baseline, 10, and 90 minutes after accomplishing the block and after the motor and sensory block resolved. Diaphragmatic excursion during deep inspiration was also evaluated 90 minutes after the block was performed, with the patient in the sitting position. RESULTS: Interscalene brachial plexus block produced diaphragmatic paralysis in all patients included in the study, as demonstrated by the pulmonary function testing and the chest radiograph. No significant differences were found in any of the parameters studied. At 10 minutes, baseline functional residual capacity had diminished by 34 +/- 10% in the 40 mL group and 37 +/- 13% in the 20 mL group. Maximum cephalad sensory dermatome level was also similar in both groups, being C 3 or above in all patients. Ipsilateral hemidiaphragmatic motion was similar in both groups (3.2 +/- 2.3 cm in the 40 mL group and 2.6 +/- 1.7 cm in the 20 mL group). However, in no case was dyspnea manifested. CONCLUSIONS: Decreasing the volume of local anesthetic and applying proximal digital pressure to the site of injection is not effective in reducing the cervical block spread and the frequency or intensity of diaphragmatic paralysis during interscalene ISB.     

Neurologic sequelae after interscalene brachial plexus block for shoulder/upper arm surgery: the association of patient, anesthetic, and surgical factors to the incidence and clinical course

We determined the incidence, distribution, and resolution of neurologic sequelae and the association with anesthetic, surgical, and patient factors after single-injection interscalene block (ISB) using levobupivacaine 0.625% with epinephrine 1:200,000 in subjects undergoing shoulder or upper arm surgery, or both, in 693 consecutive adult patients. After a standardized ISB, assessments were made at 24 and 48 h and at 2 and 4 wk for anesthesia, hypesthesia, paresthesias, pain/dysesthesias, and motor weakness. Symptomatic patients were monitored until resolution. Subjects reporting pain or discomfort >3 of 10 and those with motor or extending sensory symptoms received diagnostic assessment. Six-hundred-sixty subjects completed 4 wk of follow-up. Fifty-eight neurologic sequelae were reported by 56 subjects. Symptoms were sensory except for two cases of motor weakness (lesions identified distant from the ISB site). Thirty-one sequelae with likely ISB association were reported by 29 subjects, including 14 at the ISB site, 9 at the distal phalanx of thumb/index finger, 7 involving the posterior auricular nerve, and 1 clinical brachial plexopathy. Sequelae not likely associated with the ISB were reported by 27 subjects with symptoms reported in the median (n = 9) and ulnar (n = 4) nerves, surgical neuropraxias (n = 12), and motor weakness (n = 2). Symptoms resolved spontaneously (median 4 wk; range, 2-16 wk) except in the two patients with motor weaknesses and the patient with clinical brachial plexopathy, who received therapeutic interventions. Variables identified as independent predictors of neurologic sequelae likely related to ISB were paresthesia at needle insertion and ISB site pain or bruising at 24 h. In contrast, surgery preformed in the sitting position, as well as ISB site bruising, was identified as a predictor of neurologic sequelae not likely related to ISB. In conclusion, neurologic sequelae after single-injection ISB using epinephrine mainly involve transient minor sensory symptoms.     

Sudden severe postoperative dyspnea following shoulder surgery: Remember inadvertent phrenic nerve block due to interscalene brachial plexus block

Advanced imaging techniques, improved operative techniques, and instrumentation combined with better patient awareness and expectations have resulted in an exponential increase in upper limb surgical procedures during recent times. Surgical teams expect superior analgesia and regional blocks have matched these expectations quite often resulting in improved patient satisfaction and early rehabilitation to achieve best results. Ultrasound-guided interscalene brachial plexus block (ISB) is commonly used to provide analgesia for procedures involving shoulder girdle. We report a case of symptomatic hemi-diaphragmatic paresis (HDP) due to the phrenic nerve block following ISB for arthroscopic sub-acromial decompression of the shoulder presenting as severe postoperative dyspnea. There is strong evidence of HDP following ISB in anesthetic literature, but not reported in related surgical specialties such as orthopedics. We wish to inform upper-limb surgeons and educate junior doctors and other ancillary staff working in upper-limb units to be aware of this serious but reversible complication.     

A comparison of proximal and distal radial nerve motor responses in axillary block using triple stimulation

BACKGROUND AND OBJECTIVES: Stimulation of the radial nerve at the axilla may cause either a proximal movement (forearm extension) or distal movements (supination, wrist or finger extension). In the most recent studies on axillary block, only a distal twitch was accepted as valid. However, this approach was based only on clinical experience. The aim of this study was to verify if a proximal motor response can be considered a satisfactory endpoint. METHODS: This was a prospective, randomized, double-blinded study. One hundred fifty patients received a triple-injection axillary brachial plexus block in which the radial nerve was located by a proximal (group PROX) or a distal motor response (group DIST). Patients were assessed for sensory and motor block of the branches of the radial nerve by a blinded investigator at 5-minute intervals over 30 minutes. RESULTS: An 81% success rate for anesthetizing the sensory distal branches of the radial nerve was seen in group PROX; a significantly higher success rate was recorded in group DIST (95%). The onset time of sensory block for the distal branches of the radial nerve was significantly shorter in group DIST (9.9 +/- 6 v 15.4 +/- 7 minutes). The time to perform the block was slightly shorter and the localization of the nerve simpler in group PROX. The overall block success rate was not significantly different in the 2 groups. CONCLUSIONS: Local anesthetic injection at the proximal radial twitch significantly reduces the efficacy and prolongs the onset time of the radial nerve block. Searching for distal response is significantly more difficult and time consuming than searching for proximal response. However, it does not significantly increase patient discomfort or adverse effects.     

Needle placement and injection posterior to the axillary artery may predict successful infraclavicular brachial plexus block: a report of three cases

PURPOSE: The combined use of ultrasound and nerve stimulation for localization of the brachial plexus during infraclavicular block has not been evaluated. We describe three cases of infraclavicular block where we used ultrasound to place the needle and catheter, observe type of muscle twitch obtained and local anesthetic spread after injection. CLINICAL FEATURES: Injection of local anesthetic after obtaining proximal muscle stimulation was associated with local anesthetic spread between the axillary artery and pectoral muscle. This resulted in block failure (case 1).In case 2, proximal stimulation was associated with anterior spread after a test injection. The needle and subsequently the catheter were repositioned posterior to the axillary artery and distal muscle stimulation obtained. Injection through the catheter resulted in local anesthetic spread posterior to the artery and successful block.In case 3, no distal twitch could be obtained but in light of previous experience the needle and then the catheter were placed posterior to the axillary artery. Posterior local anesthetic spread was observed and successful block ensued despite absence of any muscle stimulation. CONCLUSION: Ultrasound guidance during infraclavicular brachial plexus block enables direct visualization of needle/catheter tip location and confirmation of appropriate local anesthetic spread. Our early experience suggests that spread of injectate posterior to the second part of the axillary artery is associated with successful block.     

Inability to consistently elicit a motor response following sensory paresthesia during interscalene block administration

BACKGROUND: Two methods of nerve block based on eliciting neural feedback with the block needle currently exist. The paresthesia technique uses sensory feedback to ascertain that the needle tip is close to the nerve. By contrast, a peripheral nerve stimulator makes use of motor responses to electrical stimulation. The relation of motor responses to an electrical peripheral nerve stimulator and sensory nerve contact (paresthesia) had not been studied. METHODS: Thirty consecutive unpremedicated patients who presented for shoulder surgery with interscalene block anesthesia were prospectively studied. Interscalene block was performed by the single paresthesia method of Winnie, using an insulated or non-insulated needle connected to a peripheral nerve stimulator with the power off. At the precise point of paresthesia, the peripheral nerve stimulator was turned on, and the current was slowly increased to 1.0 mA with a pulse width of 0.2 ms. Presence and location of any motor responses were observed and recorded. RESULTS: All patients had easily elicited paresthesias. The site of first paresthesia was to the shoulder in 73% of patients. Only 30% of patients exhibited any motor response to electrical stimulation up to 1.0 mA. There was no relation between site of paresthesia and associated motor nerve response. CONCLUSION: Elicitation of paresthesia does not translate to an ability to elicit a motor response to a peripheral nerve stimulator in the majority of patients.