The effect of needle tip tracking on procedural time of ultrasound-guided lumbar plexus block: a randomised controlled trial.

Technology that facilitates performance of deep peripheral nerve blocks is of clinical interest. The Onvision™ is a new device for ultrasonographic needle tip tracking that incorporates an ultrasound sensor on the needle tip that is then represented by a green circle on the ultrasound screen. The primary aim of this study was to investigate the effect of needle tip tracking on procedural time in the first human volunteer study. Secondary outcome measures included: number of hand movements; hand movement path length; block success rate; block onset time; block duration; discomfort experienced by the volunteers; and the anaesthetists' confidence as to whether their block would be successful. Two anaesthetists performed ultrasound-guided lumbar plexus blocks with an out-of-plane technique, with and without the use of needle tip tracking. In total, data from 25 volunteers were studied. Mean (SD) procedural time was 163 (103) s with needle tip tracking and 216 (117) s without (p = 0.10). Hand motion analysis showed that needle tip tracking was associated with a significant decrease in the mean (SD) number of intended needling hand movements (39 (29) vs. 59 (36); p = 0.03) and path lengths (3.2 (3.1) m vs. 5.5 (4.5) m; p = 0.03). No differences were found for any other secondary outcomes. The use of Onvision needle tip tracking did not reduce procedural time for out-of-plane ultrasound-guided lumbar plexus block but did reduce the number of hand movements and path lengths. This may indicate improved needle control but further studies are needed to confirm this finding.

Microcirculation and haemodynamics after infraclavicular brachial plexus block using adrenaline as an adjuvant to lidocaine: a randomised, double-blind, crossover study in healthy volunteers.

We evaluated the effect of adrenaline on human skin microcirculation (nutritive and sub-papillary) and systemic cardiovascular variables after it was added to lidocaine in infraclavicular brachial plexus blocks. Twelve healthy, non-smoking male volunteers were included, each attending two study sessions 2 weeks apart, and they were studied using a crossover design. In both sessions, they received an ultrasound-guided infraclavicular brachial plexus block in the non-dominant arm with 0.4 ml.kg-1 lidocaine, 15 mg.ml-1 with or without adrenaline 5 µg.ml-1 . Microcirculation was assessed by laser Doppler fluxmetry (sub-papillary blood flow), capillary video microscopy (nutritive blood flow) and continuous temperature measurements. Heart rate and arterial pressure were recorded continuously and non-invasively. Median (IQR [range]) sub-papillary blood flow increased substantially 30 min after the brachial plexus block, from 8.5 (4.4-13.5 [2.9-28.2]) to 162.7 (111.0-197.8 [9.5-206.7]) arbitrary units with adrenaline (p = 0.017), and from 6.9 (5.3-28.5 [1.8-42.1] to 133.7 (16.5-216.7 [1.0-445.0] arbitrary units without adrenaline (p = 0.036). Nutritive blood flow (functional capillary density, capillaries.mm-2 , measured at the dorsal side of the hand) decreased in the blocked extremity when adrenaline was used as adjuvant, from median (IQR [range]) 45 (36-52 [26-59]) to 38 (29-41 [26-42]), p = 0.028, whereas no significant change occurred without adrenaline. Median finger skin temperature (°C) increased by 44% (data pooled) with no significant differences between the groups. No significant changes were found in the systemic cardiovascular variables with or without adrenaline. We conclude that lidocaine infraclavicular brachial plexus blocks caused an increase in skin sub-papillary blood flow. The addition of adrenaline produced stronger and longer lasting blocks, but decreased the nutritive blood flow.

Pre-operative brachial plexus block compared with an identical block performed at the end of surgery: a prospective, double-blind, randomised clinical trial.

We evaluated whether pre-emptive analgesia with a pre-operative ultrasound-guided infraclavicular brachial plexus block resulted in better postoperative analgesia than an identical block performed postoperatively. Fifty-two patients undergoing fixation of a fractured radius were included. All patients received general anaesthesia with remifentanil and propofol. Patients were randomly allocated into two groups: a pre-operative block or a postoperative block with 0.5 ml.kg-1 ropivacaine 0.75%. After surgery, all patients received regular paracetamol plus opioids for breakthrough pain. Mean (SD) time to first rescue analgesic after emergence from general anaesthesia was 544 (217) min in the pre-operative block group compared with 343 (316) min in the postoperative block group (p = 0.015). Postoperative pain scores were higher and more patients required rescue analgesia during the first 4 h after surgery in the postoperative block group. There were no significant differences in plasma stress mediators between the groups. Analgesic consumption was lower at day seven in the pre-operative block group. Pain was described as very strong at block resolution in 27 (63%) patients and 26 (76%) had episodes of mild pain after 6 months. We conclude that a pre-operative ultrasound-guided infraclavicular brachial plexus block provides longer and better analgesia in the acute postoperative period compared with an identical postoperative block in patients undergoing surgery for fractured radius.

Ultrasound-guided lumbar plexus block in volunteers; a randomized controlled trial.

Background: The currently best-established ultrasound-guided lumbar plexus block (LPB) techniques use a paravertebral location of the probe, such as the lumbar ultrasound trident (LUT). However, paravertebral ultrasound scanning can provide inadequate sonographic visibility of the lumbar plexus in some patients. The ultrasound-guided shamrock LPB technique allows real-time sonographic viewing of the lumbar plexus, various anatomical landmarks, advancement of the needle, and spread of local anaesthetic injectate in most patients. We aimed to compare block procedure outcomes, effectiveness, and safety of the shamrock vs LUT. Methods: Twenty healthy men underwent ultrasound-guided shamrock and LUT LPBs (2% lidocaine­adrenaline 20 ml, with 1 ml diluted contrast added) in a blinded randomized crossover study. The primary outcome was block procedure time. Secondary outcomes were procedural discomfort, number of needle insertions, injectate spread assessed with magnetic resonance imaging, sensorimotor effects, and lidocaine pharmacokinetics. Results: The shamrock LPB procedure was faster than LUT (238 [sd 74] vs 334 [156] s; P=0.009), more comfortable {numeric rating scale 0­10: 3 [interquartile range (IQR) 2­4] vs 4 [3­6]; P=0.03}, and required fewer needle insertions (2 [IQR 1­3] vs 6 [2­12]; P=0.003). Perineural injectate spread seen with magnetic resonance imaging was similar between the groups and consistent with motor and sensory mapping. Zero/20 (0%) and 1/19 (5%) subjects had epidural spread after shamrock and LUT (P=1.00), respectively. The lidocaine pharmacokinetics were similar between the groups. Conclusions: Shamrock was faster, more comfortable, and equally effective compared with LUT. Clinical trial registration: NCT02255591

Does dexamethasone have a perineural mechanism of action? A paired, blinded, randomized, controlled study in healthy volunteers.

BACKGROUND: Dexamethasone prolongs block duration. Whether this is achieved via a peripheral or a central mechanism of action is unknown. We hypothesized that perineural dexamethasone added as an adjuvant to ropivacaine prolongs block duration compared with ropivacaine alone, by a locally mediated effect when controlled for a systemic action. METHODS: We performed a paired, blinded, randomized trial, including healthy men. All subjects received bilateral blocks of the saphenous nerve with ropivacaine 0.5%, 20 ml mixed with dexamethasone 2 mg in one leg and saline in the other, according to randomization. The primary outcome was the duration of sensory block assessed by temperature discrimination in the saphenous nerve distribution. Secondary outcomes were sensory block assessed by mechanical discrimination, pain response to tonic heat stimulation, and warmth and heat pain detection thresholds. RESULTS: We included 20 subjects; one had a failed block and was excluded from the paired analysis. Block duration was not statistically significantly longer in the leg receiving dexamethasone when assessed by temperature discrimination (primary outcome, estimated median difference 1.5 h, 95% confidence interval -3.5 to 0, P=0.050). For all other outcomes, the duration was statistically significantly longer in the leg receiving dexamethasone, but the median differences were <2.0 h. Individual subject analysis revealed that only eight subjects had a block prolongation of at least 2 h in the leg receiving dexamethasone perineurally. CONCLUSION: Perineural administration of dexamethasone 2 mg showed a modest and inconsistent effect of questionable clinical relevance on block duration. CLINICAL TRIAL REGISTRATION: NCT01981746.

Ultrasound controlled nerve stimulation in the elbow region: high currents and short distances needed to obtain motor responses.

BACKGROUND: Electrical nerve stimulation is commonly used to perform peripheral nerve blocks. The purpose of this study was to investigate the relation between stimulating currents and the distance between the needle-tip and stimulated nerves. METHODS: In 18 volunteers the radial and ulnar nerves were stimulated in the elbow region from opposite directions. Needle-to-nerve distances were measured by high-frequency ultrasound when motor responses to electrical stimulation were elicited with currents of 5, 2, 1 and 0.5 mA and impulse widths of 0.1 ms. Additionally, current thresholds for nerve stimulation were identified when the needle-tip was in contact with the nerve. RESULTS: The ulnar nerves responded to electrical stimulation from a significantly greater distance than the radial nerves. Threshold levels at needle-to-nerve contact ranged from 0.4 to 4.5 mA for the radial nerve and from 0.32 to 2.0 mA for the ulnar nerve. They were significantly lower for the ulnar nerve than for the radial nerve. Currents required to obtain neuromuscular responses often exceeded the recommended current levels for nerve stimulation. CONCLUSIONS: Our results show significant differences in the ease of stimulation between the radial and ulnar nerves. High current thresholds and short nerve-to-needle distances were often needed to obtain neuromuscular responses in two nerves in the elbow region.