Cutaneous sensory block area of the ultrasound-guided subcostal transversus abdominis plane block: an observational study.

BACKGROUND AND OBJECTIVES: The transversus abdominis plane block (TAP) can be applied using different approaches, resulting in varying cutaneous analgesic distributions. This study aimed to assess the cutaneous sensory block area (CSBA) after ultrasound-guided TAP (US-TAP) using the subcostal approach. METHODS: Thirty patients undergoing elective laparoscopic cholecystectomy received a subcostal US-TAP with 20 mL 2.5 mg/mL ropivacaine bilaterally. Measurements were performed 150 min after block application. The CSBA was mapped using cold sensation and a sterile marker, photodocumented, and transferred to a transparency. The area of the CSBA was calculated from the transparencies. RESULTS: The median CSBA of the subcostal US-TAP was 174 cm2 (IQR 119-219 cm2; range 52-398 cm2). In all patients, the CSBA had a periumbilical distribution. In 42 of the 60 (70%) unilateral blocks, the CSBA had both an epigastric and infraumbilical component; in 12 of the 60 (20%) unilateral blocks, it covered only the epigastrium; and in 4 of the 60 (7%) unilateral blocks, it had only an infraumbilical distribution. No CSBA was found in 2 of the 60 (3%) unilateral blocks. In none of the patients did the CSBA cover the abdominal wall lateral to a vertical line through the anterior superior iliac spine. CONCLUSION: The subcostal US-TAP results in a heterogeneous non-dermatomal CSBA with varying size and distribution across the medial abdominal wall.

Mixing short- and long-acting local anaesthetics in peripheral nerve blocks: Protocol for a systematic review and meta-analysis.

INTRODUCTION: This protocol describes a systematic review and meta-analysis to evaluate the clinical effects of mixing short- and long-acting local anaesthetics in peripheral nerve blocks. Clinicians often combine short- and long-acting local anaesthetics to achieve a briefer onset time. However, this may come with a prize, namely a shorter total duration of the block, which is of clinical importance. OBJECTIVE: This systematic review aims to strengthen the knowledge of the clinical effects associated with this practice. The primary outcome is the duration of block analgesia. Secondary outcomes are block onset time, sensory and motor block duration. Exploratory outcomes are postoperative pain scores, cumulative 24-h opioid consumption and the prevalence of serious adverse events. METHODS: We will conduct a meta-analysis of the extracted data, and the risk of bias for each study will be evaluated. We will perform a Trial Sequential Analysis, subgroup, and sensitivity analyses and assess the overall risk of publication bias. Finally, we will evaluate the review using the GRADE principles.

Peripheral nerve blocks for closed reduction of distal radius fractures-A protocol for a systematic review.

BACKGROUND: Current methods of anaesthesia used for closed reduction of distal radial fractures may be insufficient for pain relief and muscle relaxation, potentially compromising reduction quality and patient satisfaction. Peripheral nerve blocks have already been implemented for surgery of wrist fractures and may provide optimal conditions for closed reduction due to complete motor and sensory blockade of the involved nerves. However, existing literature on peripheral nerve blocks for closed reduction is sparse, and no updated systematic review or meta-analysis exists. AIMS: This protocol is developed according to the PRISMA-P statement. The systematic review and meta-analysis aim to consolidate the literature regarding the effect and harm of peripheral nerve blocks compared with other anaesthesia modalities for closed reduction of distal radius fractures in adults. METHODS: The two primary outcomes are the proportion of participants needing surgery after closed reduction and pain during closed reduction. We will only include randomised clinical trials. Two review authors will each independently screen literature, extract data, and assess risk of bias with Risk of Bias 2 Tool. Meta-analysis will be carried out with Rstudio. We will also perform a Trial Sequential Analysis. The certainty of evidence will be judged using GRADE guidelines. DISCUSSION: We will use up-to-date methodology when conducting the systematic review outlined in this protocol. The results may guide clinicians in their decision-making regarding the use of anaesthesia for closed reduction of distal radius fractures in adults.

Single injection combined suprascapular and axillary nerve block: A randomised controlled non-inferiority trial in healthy volunteers.

BACKGROUND: A shoulder block without lung affection is desirable. In this study, we compared a low versus a high volume of a modified supraclavicular brachial plexus block. We hypothesised that a low volume of local anaesthetic would provide non-inferior block success rate with better preserved lung function. METHODS: Healthy volunteers were randomised to receive ultrasound guided 5 or 20 ml ropivacaine 0.5% at the departure of the suprascapular nerve from the brachial plexus. Primary outcome was successful shoulder block-defined as cutaneous sensory affection of the axillary nerve and motor affection of the suprascapular nerve (>50% reduction in external rotation force measured with dynamometry). We used a non-inferiority margin of 20%. Secondary outcome was change in lung function measured with spirometry. RESULTS: Thirteen of 16 (81.3%; 95% confidence interval [CI] 57.0% to 93.4%) in the 5 ml group and 15 of 16 (93.8%; 95% CI 71.7% to 98.9%) in the 20 ml group had successful shoulder block (p = .6). The ratio of the event rates of the 20 ml (standard) and 5 ml (intervention) groups was (15/16)/(13/16) = 0.937/0.813 = 1.15 (95% CI 0.88 to 1.51). All mean reductions in lung function parameters were non-significantly lower in the 5 ml group compared with the 20 ml group. CONCLUSION: For our primary outcome, the 95% CI of the difference of event ratio included the non-inferiority margin. We are therefore unable to conclude that 5 ml LA is non-inferior to 20 ml LA with respect to block success rate.

Ultrasound-guided peripheral nerve blocks for preoperative pain management in hip fractures: a systematic review.

Systematic reviews associate peripheral nerve blocks based on anatomic landmarks or nerve stimulation with reduced pain and need for systemic analgesia in hip fracture patients. We aimed to investigate the effect of ultrasound-guided nerve blocks compared to conventional analgesia for preoperative pain management in hip fractures. Five databases were searched until June 2021 to identify randomised controlled trials. Two independent authors extracted data and assessed risk of bias. Data was pooled for meta-analysis and quality of evidence was evaluated using Grades of Recommendation Assessment, Development and Evaluation (GRADE). We included 12 trials (976 participants) comparing ultrasound-guided nerve blocks to conventional systemic analgesia. In favour of ultrasound, pain measured closest to two hours after block placement decreased with a mean difference of -2.26 (VAS 0 to 10); (p < 0.001) 95% CI [-2.97 to -1.55]. In favour of ultrasound, preoperative analgesic usage of iv. morphine equivalents in milligram decreased with a mean difference of -5.34 (p=0.003) 95% CI [-8.11 to -2.58]. Time from admission until surgery ranged from six hours to more than three days. Further, ultrasound-guided nerve blocks may be associated with a lower frequency of delirium: risk ratio 0.6 (p = 0.03) 95% CI [0.38 to 0.94], fewer serious adverse events: risk ratio 0.33 (p = 0.006) 95% CI [0.15 to 0.73] and higher patient satisfaction: mean difference 25.9 (VAS 0 to 100) (p < 0.001) 95% CI [19.74 to 32.07]. However, the quality of evidence was judged low or very low. In conclusion, despite low quality of evidence, ultrasound-guided blocks were associated with benefits compared to conventional systemic analgesia.

Low volume proximal suprascapular nerve block after arthroscopic shoulder surgery - A randomised, controlled trial.

BACKGROUND: A proximal suprascapular nerve block has been suggested as an alternative to an interscalene brachial plexus block after arthroscopic shoulder surgery. The aim of this randomised controlled trial was to compare the analgesic and opioid-sparing effect of a low volume proximal suprascapular nerve block with placebo in patients with moderate-to-severe pain after arthroscopic shoulder surgery. METHODS: Patients with a VAS score equal to or above 50 during the first postoperative hour after planned arthroscopic shoulder surgery were included in the study. They were randomised to an ultrasound-guided proximal suprascapular nerve block with either 5 ml ropivacaine 7.5 mg/ml or 5 ml isotonic NaCl. Primary outcome was change in VAS score at rest from baseline to 30 min after the block procedure (T30). Secondary outcomes included total morphine consumption from 0-6 h after block procedure. RESULTS: There was a significant difference in mean VAS reductions at T30 between the two groups favouring the ropivacaine group (-50.2 vs -26.8, p < .001). Total intravenous morphine consumption from 0-6 h after block procedure was significantly lower in the ropivacaine group compared to the placebo group (8.5 mg vs 18.5 mg, p < .01). CONCLUSION: In this study, a proximal suprascapular nerve block with only 5 ml ropivacaine resulted in a substantial pain reduction and opioid-sparing effect in patients with VAS of 50 or more after arthroscopic shoulder surgery.

Programmed, intermittent boluses versus continuous infusion to the sciatic nerve - a non-inferiority randomized, controlled trial.

BACKGROUND: Trials comparing programmed, intermittent boluses (PIB) and continuous infusion in catheter-based nerve blocks found no analgesic differences. However, as these trials used equal doses of local anesthetic (LA), the time of action of each bolus was not accounted for. Therefore, the dose-sparing benefits of PIB may have been overlooked. We compared the analgesic effect of boluses administered in intervals resembling the time of action of each bolus with continuous infusion. We hypothesized that PIB provided non-inferior analgesia despite consuming less LA. METHODS: Eighty-one patients undergoing fore- and midfoot surgery receiving a catheter-based sciatic nerve block were randomized to ropivacaine 0.2% as PIB of 10 ml every 8th hour or as continuous infusion, 6 ml h-1 . All participants could also receive boluses of 10 ml every 4th hour as needed. A non-inferiority randomized controlled design was used. Primary outcome was pain (VAS, 0-100 mm) for 72 h using area under curve (AUC) calculation. We assumed a linear relationship between mean VAS and AUC-VAS and used a non-inferiority margin of VAS = 20 mm, corresponding to AUC-VAS = 1440 mm h. RESULTS: Mean difference in AUC-VAS was -416 mm h (95% CI -1076 to 244; p = .217) between continuous infusion (mean AUC-VAS 1206 mm h) and PIB (mean AUC-VAS 1621 mm h), establishing non-inferiority. Mean total LA consumption was significantly larger for continuous infusion compared to PIB ((468 ml (95% CI 458 to 478) vs. 136 ml (95% CI 123 to 148); p < 0.0001)). CONCLUSIONS: PIB provided non-inferior analgesia compared to continuous infusion for 72 postoperative hours despite using significantly less LA.

Intraindividual variation of the transversus abdominis plane block: an exploratory study in healthy volunteers.

INTRODUCTION: The transversus abdominis plane block is widely used in postoperative pain management after abdominal surgery. However, large interindividual variation in the cutaneous distribution area of the block has been demonstrated. The purpose of the present study was to explore the reproducibility of the block by determining the intraindividual variation when repeating the block on two separate days. METHODS: Ultrasound-guided posterior transversus abdominis plane blocks were performed in 16 healthy volunteers and repeated after at least 2 days. Cutaneous sensory block areas and distributions, thresholds for mechanical stimulation, abdominal muscle thicknesses at rest and during maximal contraction, waist circumferences and block duration times were measured on both days. Outcome measurements from the 2 days were compared using a one-sample t-test and intraclass correlation coefficients were calculated for each parameter. Agreement was evaluated visually using Bland-Altman plots. RESULTS: None of the mean values of the outcome measurements differed significantly between the 2 days. Intraclass correlation coefficient was 0.75 (moderate-to-good reliability) for lateral abdominal muscle thickness during maximal contraction, but ranges from -0.07 to 0.67 were found for all other outcome measurements (poor-to-moderate reliability). CONCLUSION: We found a moderate-to-good reproducibility for lateral abdominal muscle thickness during maximal voluntary contraction, but a moderate-to-poor reproducibility for all other block characteristics. However, the cutaneous distribution of the block was still located primarily inferior to a horizontal line through the umbilicus and lateral relative to a vertical line through the anterior superior iliac spine.

A randomized controlled trial evaluating the impact of selective axillary nerve block after arthroscopic subacromial decompression.

BACKGROUND: The sensory innervation of the shoulder is complex and there are variations in the branching patterns of the sensory fibres. Articular branches from the axillary nerve to the subacromial bursa are described in more than 50% of investigated shoulders but the isolated contribution of sensory input from the axillary nerve has never been investigated clinically. We hypothesized that a selective block of the axillary nerve would reduce morphine consumption and pain after arthroscopic subacromial decompression. METHODS: We included 60 patients in a randomized, blinded, placebo-controlled study. Patients were randomized to a preoperative selective ultrasound-guided axillary nerve block with 20 mL ropivacaine (7.5 mg/mL) or 20 mL saline. Primary outcome was intravenous morphine consumption 0-4 h postoperatively. Secondary outcome was postoperative pain evaluated by a visual analogue scale (VAS) score (0-100). RESULTS: We analysed data from 50 patients and found no significant difference in 0-4 h postoperative morphine consumption between the two groups (ropivacaine 14 mg, placebo 18 mg (P = 0.12)). There was a reduction in postoperative pain: VAS 0-4 h (area under the curve) (ropivacaine 135, placebo 182 (P = 0.03)), VAS after 8 h (ropivacaine 9, placebo 20 (P = 0.01)) and VAS after 24 h (ropivacaine 7, placebo 18 (P = 0.04)). Eight out of 19 patients with a successful selective axillary nerve block needed an interscalene brachial plexus escape block. CONCLUSIONS: Selective block of the axillary nerve has some pain relieving effect, but in this setting the effect was unpredictable, variable and far from sufficient in a large proportion of the patients. TRIAL REGISTRATION: ClinicalTrials.gov (NCT01463865). Registered: November 1, 2011.

Push-pull thiophene chromophores for electro-optic applications: from 1D linear to ß-branched structures.

We report the synthesis and characterization of a novel series of push-pull chromophores bearing 1D linear and ß-branched thiophenes as π-conjugated spacers between a 2,2,4,7-tetramethyl-1,2,3,4-tetrahydroquinoline electron donor unit and dicyano- and tricyanovinylene electron acceptor groups. The effect of the introduction of ß-thiophenes on the linear and nonlinear (NLO) optical properties as well as electrochemical and thermal data is studied in detail by performing a comparative study between the branched and 1D linear systems. In addition, a parallel DFT computational study is used to evaluate structure-property relationships. The non-linear optical behavior of the molecules both in solution and in solid state as electro-optic (EO) films using a guest-host approach shows very promising performance for electro-optic applications with high molecular first hyperpolarizabilities (µß) of 4840 × 10-48 esu and electro-optic coefficients r33 reaching 650 pm V-1. One highlight is that the electro-optic films of the ß-branched chromophores are superior in terms of thermal stability in device operation as measured by a transmissive modified reflective Teng-Man method. This work provides guidelines for the design of improved electro-optic materials including ß-branched chromophores which could be useful for practical EO applications, where both enhanced ß and r33 values together with chemical and thermal stability are necessary.

Longitudinal neural exposure to local anesthetic and nerve block duration: a retrospective analysis of experimental data from healthy volunteer trials.

BACKGROUND AND OBJECTIVES: Characteristics of a nerve block depend on the distribution of local anesthetic (LA) close to the nerve. The relationship between longitudinal distribution of LA and nerve block characteristics has not been investigated in vivo, but one in vitro study showed decrements in action potential amplitudes with increasing exposure length. We describe the influence of longitudinal neural exposure to LA on nerve block duration adjusted for other likely influential factors. METHODS: We analyzed data from an ethical board approved prospective consecutive collected dataset of 180 healthy volunteers with a common peroneal nerve block (2.5-20 mL, 5-40 mg of ropivacaine). Data were retrieved from three independent randomized controlled trials. The longitudinal neural exposure to LA in millimeters was evaluated using ultrasound. Interventional covariates and demographics were retrieved. Nerve block duration, the dependent variable in the primary assessment, was defined as time of insensitivity to a cold stimulus and was evaluated blinded to all other covariates. Using a multiple linear mixed-effects model, we explored the association between neural exposure to LA and nerve block duration. RESULTS: We found a significant positive association between longitudinal neural exposure to LA and block duration (p<0.01). A 10% increase in longitudinal exposure resulted in an 8.7 (2.5; 15) min increase in block duration. LA dose was associated to block duration (p<0.001) but LA volume had no impact (p=0.93). CONCLUSIONS: Longitudinal neural exposure to LA was significantly associated with nerve block duration. LA dose was the strongest determinant for block duration whereas LA volume had no influence.

The effect of ropivacaine concentration on common peroneal nerve block duration using a fixed dose: A randomised, double-blind trial in healthy volunteers.

BACKGROUND: The effect of local anaesthetic concentration on peripheral nerve block duration is unclear. Recent clinical trials found nerve blocks of equivalent duration despite changing local anaesthetic concentration but with a fixed local anaesthetic dose. A criticism of these studies is that the local anaesthetic doses used were above the proposed local anaesthetic dose-duration ceiling level, masking any potential effect of different local anaesthetic concentrations on nerve block duration. OBJECTIVE: We investigated the effect of local anaesthetic concentration on nerve block duration using a fixed local anaesthetic dose below the local anaesthetic dose-duration ceiling level. We hypothesised that changing local anaesthetic concentration would affect nerve block duration. DESIGN: Randomised, double-blind trial. SETTING: Single-centre, academic hospital. PARTICIPANTS: Healthy volunteers. INTERVENTIONS: Each participant received an ultrasound-guided common peroneal nerve block with a fixed dose of 10 mg of ropivacaine dissolved in either 2.5, 5, 10, 15 or 20 ml of 0.9% saline according to group allocation, yielding local anaesthetic concentrations of 4, 2, 1, 0.67 and 0.5 mg ml. MAIN OUTCOME MEASURES: The primary outcome was duration of sensory block defined as altered or no sensitivity to a cold stimulus. The secondary outcome was duration of motor block defined as either paresis or paralysis. Intergroup differences were tested using one-way Analysis of variance . RESULTS: All participants had sensory block, and 56 out of 60 participants had motor block. From the highest to the lowest concentration groups, mean ±â€ŠSD sensory block durations were 13.1 ±â€Š2.7, 13.4 ±â€Š3.3, 12.6 ±â€Š3.9, 10.4 ±â€Š2.9 and 11.0 ±â€Š2.1 h (P = 0.073), and mean ±â€ŠSD motor block durations were 8.5 ±â€Š2.0, 7.9 ±â€Š3.0, 6.1 ±â€Š3.1, 5.9 ±â€Š3.5, 4.0 1.9 h (P = 0.002). CONCLUSION: In contrast to our hypothesis, we found no changes in mean sensory nerve block duration. However, local anaesthetic dilution resulted in reduced motor block duration. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03326609.

Volume of ropivacaine 0.2% and sciatic nerve block duration: A randomized, blinded trial in healthy volunteers.

BACKGROUND: Sciatic nerve blocks are used for many orthopaedic procedures on the knee, lower leg, foot and ankle. However, as nerve block durations vary considerably, the timing of supplemental analgesia is challenging. Therefore, knowledge on the effect of local anaesthetic (LA) dose on block duration is important to outweigh the benefits of increasing LA dose against the risk of LA systemic toxicity. In this randomized, double-blind trial, we aimed to explore the relationship between the volume of ropivacaine 0.2% and sciatic nerve block duration. We hypothesized that increasing LA volume would prolong block duration. METHODS: We randomized 60 healthy volunteers to receive one of five volumes of ropivacaine 0.2%: 5, 10, 15, 20, or 30 mL. We used an ultrasound-guided, catheter-based technique targeting the sciatic nerve in the infragluteal region. The primary outcome was sensory block duration defined as the time of insensitivity to a cold stimulus. Intergroup differences were tested using one-way ANOVA. RESULTS: Mean (SD) sensory block durations for the tibial nerve (TN) with increasing volume were: 9.3 hours (1.7), 10.4 hours (1.6), 9.7 hours (2.9), 10.7 hours (2.8) and 9.9 hours (2.6). Mean (SD) sensory block durations for the common peroneal nerve (CPN) were: 10.6 hours (2.7), 11.9 hours (1.5), 11.0 hours (3.3), 13.2 hours (3.7), and 13.5 hours (6.1). There were no intergroup differences (P = .67 [TN]; P = .25 [CPN]). CONCLUSION: We found no effect of increasing the volume of ropivacaine 0.2% from 5 to 30 mL on sensory sciatic nerve block duration.

Intra- and inter-Individual variability in nerve block duration: A randomized cross-over trial in the common peroneal nerve of healthy volunteers.

BACKGROUND: The reported variation in nerve block duration is considerable. To individualize nerve block therapy, knowledge of the intra- vs inter-individual variability is essential. We investigated the relative contribution of these 2 parameters to the overall nerve block duration variability. METHODS: With ethics committee approval, we conducted a randomized cross-over trial where 20 healthy volunteers received 8 common peroneal nerve blockades with lidocaine 0.5% on 4 consecutive days. Allocations were 5 mL to either the right or left side and 10 mL to the opposite side on day 1 and 2 and vice versa on day 3 and 4. With fixed needle entry and nerve target, we repeated local anaesthetic deposition for each blockade. The primary outcome was variation in duration of sensory nerve block defined as insensitivity to a cold stimulus. Data were analysed using linear mixed model regression. RESULTS: The mean sensory block duration of 380 (95% CI = [342; 418]) minutes on day one was 55 [33; 77] minutes longer than on day two (P < .001), but there were no differences in mean duration between days 2, 3 and 4. The ratios with 2.5; 97.5 percentiles between inter- and intra-individual variation were 2.4 [0.8; 5.2] for the 5 mL blockades and 3.0 [0.9; 6.7] for the 10 mL blockades. The probabilities of inter- to intra-individual variation-ratios >1 were 96% and 97%. CONCLUSION: The intra-individual variability is a substantially minor contributor to the overall variability in sensory nerve block duration compared with the inter-individual variability.

Adductor canal block with a suture-method catheter - A parallel or perpendicular approach?

BACKGROUND: We performed a randomised blinded pilot study in 16 healthy volunteers to assess whether placing a suture-method catheter in the adductor canal is feasible with two different insertion techniques. METHODS: Each volunteer had a suture-method catheter placed approximately halfway between the superior anterior iliac spine and base of the patella in both legs. Catheters were placed using a parallel technique in one leg and a perpendicular technique in the other leg, according to randomisation. 15 mL lidocaine 1% was injected in each catheter. Successful placement was defined as loss of cold sensation in the saphenous area 30 min after injection. Volunteers were sent home and returned the following day and another dose of lidocaine (15 mL, 1%) was injected through the catheters. Catheter displacement distance was assessed by ultrasound and cold sensation was assessed. In case of preserved cold sensation, we attempted to reposition the catheter with a subsequent injection of lidocaine and reassessment of cold sensation. RESULTS: All primary placements were successful using the perpendicular approach (100%; 95% CI 81%-100%) whereas one placement failed using the parallel approach (94%; 95% CI 72%-99%). Three catheters placed using the perpendicular approach were displaced on day 2, compared to one catheter placed with the parallel approach. Displacement distance was highly variable. All catheters, except one, could be repositioned. Three volunteers reported transient sensory deficits lasting approximately 6-8 weeks. CONCLUSION: The suture-method catheter can be placed in the adductor canal with high success rates for initial placement with both techniques.

Ultrasound guided repositioning of a new suture-method catheter for adductor canal block - a randomized pilot study in healthy volunteers.

BACKGROUND: We performed a randomized, blinded pilot study in 12 volunteers to assess the feasibility to reposition an intentionally displaced suture-method catheter for two different insertion techniques for adductor canal block. METHODS: Each volunteer had an ultrasound-guided suture-method catheter placed in the adductor canal (AC) in both legs. The catheters were placed using a perpendicular technique in one leg and a parallel technique in the other leg, according to randomization. 15 mL lidocaine 1% (LA) was injected in each catheter. Successful primary placement was defined as combined LA spread within the AC and loss of cold sensation 15 min after injection. All catheters were intentionally displaced, and subsequently repositioned using ultrasound. Another dose of lidocaine (15 mL 1%) was injected through the catheters and assessed for successful repositioning. RESULTS: Successful primary placement was achieved in 83% (95% CI 55-95%) of catheters placed perpendicular to the AC, and in 75% (95% CI 47-91%) of catheters placed parallel to the AC. Of those with successful primary placement, 100% (95% CI 72-100%) of catheters placed perpendicular to the AC, and 67% (95% CI 35-88%)) placed parallel to the AC could be repositioned. CONCLUSIONS: Placement and secondary repositioning after displacement of a suture-method catheter within the adductor canal is achievable. A perpendicular technique seems more reliable. TRIAL REGISTRATION: NCT03315481 clinicaltrials.gov . The study was submitted on March 1, 2017. Due to clerical error, the study was posted on October 20, 2017.

An in Vivo Mouse Model to Investigate the Effect of Local Anesthetic Nanomedicines on Axonal Conduction and Excitability.

Peripheral nerve blocks (PNBs) using local anesthetic (LA) are superior to systemic analgesia for management of post-operative pain. An insufficiently short PNB duration following single-shot LA can be optimized by development of extended release formulations among which liposomes have been shown to be the least toxic. In vivo rodent models for PNB have focused primarily on assessing behavioral responses following LA. In a previous study in human volunteers, we found that it is feasible to monitor the effect of LA in vivo by combining conventional conduction studies with nerve excitability studies. Here, we aimed to develop a mouse model where the same neurophysiological techniques can be used to investigate liposomal formulations of LA in vivo. To challenge the validity of the model, we tested the motor PNB following an unilamellar liposomal formulation, filled with the intermediate-duration LA lidocaine. Experiments were carried out in adult transgenic mice with fluorescent axons and with fluorescent tagged liposomes to allow in vivo imaging by probe-based confocal laser endomicroscopy. Recovery of conduction following LA injection at the ankle was monitored by stimulation of the tibial nerve fibers at the sciatic notch and recording of the plantar compound motor action potential (CMAP). We detected a delayed recovery in CMAP amplitude following liposomal lidocaine, without detrimental systemic effects. Furthermore, CMAP threshold-tracking studies of the distal tibial nerve showed that the increased rheobase was associated with a sequence of excitability changes similar to those found following non-encapsulated lidocaine PNB in humans, further supporting the translational value of the model.

Local Anesthetic Injection Speed and Common Peroneal Nerve Block Duration: A Randomized Controlled Trial in Healthy Volunteers.

BACKGROUND AND OBJECTIVES: The speed of local anesthetic (LA) injections in peripheral regional anesthesia ranges from slow continuous infusions (3-12 mL/h) to rapid manual injections (>7500 mL/h). Optimizing injection speed could augment the spread of LA toward the targeted nerves and influence nerve block characteristics. The objective of this study was to investigate whether injection speed of a single dose of LA affects peripheral nerve block duration. METHODS: After approval from the Danish Regional Scientific Ethics Committee, we enrolled 60 healthy adult volunteers. We used an ultrasound-guided catheter-based technique to perform a common peroneal nerve block. Participants were randomized to receive 4.0 mL of ropivacaine 0.2% with 1 of 5 injection speeds: 12, 60, 300, 600, or 1800 mL/h. Investigators and participants were blinded to group assignment and intervention. Primary outcome was duration of sensory nerve block defined by insensitivity toward cold. Secondary outcomes were duration of motor nerve block, time to onset of sensory nerve block, and grades of sensory and motor nerve block.Intergroup differences were tested by one-way analysis of variance. RESULTS: We found no differences in sensory block duration between the 5 groups. Durations were median [range]: 11 [6-14], 12 [9-14], 10.5 [2-15], 11 [8-17], and 12 [9-18] hours, respectively (P = 0.294). In addition, we found no differences in secondary outcomes. CONCLUSIONS: Injection speed of LA in the range of 12 to 1800 mL/h did not affect common peroneal nerve block duration. CLINICAL TRIAL REGISTRATION: This study was registered at ClinicalTrials.gov, identifier NCT02801799.

"Eyeball test" of thermographic patterns for predicting a successful lateral infraclavicular block.

PURPOSE: Increased distal skin temperature can be used to predict the success of lateral infraclavicular (LIC) block. We hypothesized that an "eyeball test" of specific infrared thermographic patterns after LIC block could be used to determine block success. METHODS: In this observational study, five observers trained in four distinct thermographic patterns independently evaluated thermographic images of the hands of 40 patients at baseline and at one-minute intervals for 30 min after a LIC block. Sensitivity, specificity, and predictive values of a positive and a negative test were estimated to evaluate the validity of specific thermographic patterns for predicting a successful block. Sensory and motor block of the musculocutaneous, radial, ulnar, and median nerves defined block success. Fleiss' kappa statistics of multiple interobserver agreements were used to evaluate reliability. RESULTS: As a diagnostic test, the defined specific thermographic patterns of the hand predicted a successful block with increasing accuracy over the 30-min observation period. Block success was predicted with a sensitivity of 92.4% (95% confidence interval [CI], 86.8 to 96.2) and with a specificity of 84.0% (95% CI, 70.3 to 92.4) at min 30. The Fleiss' kappa for the five observers was 0.87 (95% CI, 0.77 to 0.96). CONCLUSION: We conclude that visual evaluation by an eyeball test of specific thermographic patterns of the blocked hands may be useful as a valid and reliable diagnostic test for predicting a successful LIC block.