Development and Usability of an Inexpensive and Reusable Phantom for Ultrasound-Guided Needle Cannulation.

Introduction Ultrasound-guided peripheral venous catheter placement (UG-PVCP) is a key skill for establishing intravenous access, especially in patients with anatomical challenges. Ultrasound is highly operator-dependent, and it is essential to ensure a sufficient level of competence when educating healthcare professionals. Competence can be acquired through simulation-based training (SBT) using phantoms or simulators. We developed a phantom for SBT, and in this study, we explore the phantom's usability and technical fidelity. Methods Novices with no experience in UG-PVCP and experts who routinely performed the procedure were asked to perform three ultrasound-guided catheter placement attempts on the phantom. Afterward, they were asked to complete a usability questionnaire consisting of 14 questions exploring the usability and fidelity of the phantom. Results Fifty-seven participants were included in the study: 29 novices and 28 experts. When assessing positive questions about the frequency of use, ease of use, integration of functionality, quickness to learn, and confidence level, the study showed a median score of 4 to 5 out of 5 in the two groups. The median was 1 to 2 out of 5 for negative questions assessing cumbersomeness, unnecessary complexity, and model inconsistency. In an additional comment textbox, one participant mentioned that the cannulation did not feel realistic but that it was good for cannulation practice. Conclusions We believe the phantom is suitable for an educational curriculum since it shows a high level of usability, scoring high on positive questions while scoring low on negative questions, and having high functional fidelity.

Three alginate lyases provide a new gut Bacteroides ovatus isolate with the ability to grow on alginate.

Humans consume alginate in the form of seaweed, food hydrocolloids, and encapsulations, making the digestion of this mannuronic acid (M) and guluronic acid (G) polymer of key interest for human health. To increase knowledge on alginate degradation in the gut, a gene catalog from human feces was mined for potential alginate lyases (ALs). The predicted ALs were present in nine species of the Bacteroidetes phylum, of which two required supplementation of an endo-acting AL, expected to mimic cross-feeding in the gut. However, only a new isolate grew on alginate. Whole-genome sequencing of this alginate-utilizing isolate suggested that it is a new Bacteroides ovatus strain harboring a polysaccharide utilization locus (PUL) containing three ALs of families: PL6, PL17, and PL38. The BoPL6 degraded polyG to oligosaccharides of DP 1-3, and BoPL17 released 4,5-unsaturated monouronate from polyM. BoPL38 degraded both alginates, polyM, polyG, and polyMG, in endo-mode; hence, it was assumed to deliver oligosaccharide substrates for BoPL6 and BoPL17, corresponding well with synergistic action on alginate. BoPL17 and BoPL38 crystal structures, determined at 1.61 and 2.11 Å, respectively, showed (α/α)6-barrel + anti-parallel ß-sheet and (α/α)7-barrel folds, distinctive for these PL families. BoPL17 had a more open active site than the two homologous structures. BoPL38 was very similar to the structure of an uncharacterized PL38, albeit with a different triad of residues possibly interacting with substrate in the presumed active site tunnel. Altogether, the study provides unique functional and structural insights into alginate-degrading lyases of a PUL in a human gut bacterium.IMPORTANCEHuman ingestion of sustainable biopolymers calls for insight into their utilization in our gut. Seaweed is one such resource with alginate, a major cell wall component, used as a food hydrocolloid and for encapsulation of pharmaceuticals and probiotics. Knowledge is sparse on the molecular basis for alginate utilization in the gut. We identified a new Bacteroides ovatus strain from human feces that grew on alginate and encoded three alginate lyases in a gene cluster. BoPL6 and BoPL17 show complementary specificity toward guluronate (G) and mannuronate (M) residues, releasing unsaturated oligosaccharides and monouronic acids. BoPL38 produces oligosaccharides degraded by BoPL6 and BoPL17 from both alginates, G-, M-, and MG-substrates. Enzymatic and structural characterization discloses the mode of action and synergistic degradation of alginate by these alginate lyases. Other bacteria were cross-feeding on alginate oligosaccharides produced by an endo-acting alginate lyase. Hence, there is an interdependent community in our guts that can utilize alginate.

Enantioconvergent 6π Electrocyclization Enabled by Photoredox Racemization.

This study presents a novel photoredox-enabled enantioconvergent catalytic strategy used to construct chiral 2H-1,3-benzoxazines via an unprecedented oxa-6π electrocyclization utilizing racemic α-substituted glycinates as substrates. The approach leverages a cobalt-based chiral Lewis acid catalyst, which promotes the transformation under thermal or photoredox conditions. While the thermal reaction selectively converts only the (S)-configured glycinates into enantioenriched 2H-1,3-benzoxazines (up to 96:4 e.r.), the addition of 0.5 mol % of a commercially available iridium photocatalyst under visible light irradiation transforms the reaction into an enantioconvergent process. Detailed mechanistic and time course studies of optically pure α-deuterated substrates revealed the presence of an enantiospecific kinetic isotope effect, which helped to clarify the role of both the photo- and chiral Lewis acid catalyst in the reaction sequence. In this dual catalytic system, the photocatalyst promotes a dynamic interconversion between the substrate enantiomers─a process not accessible via ground-state chemistry─while the chiral Lewis acid selectively transforms only the (S)-configured substrates. Further mechanistic evidence for the proposed mechanism is provided by linear free energy relationship analysis, which suggests that the stereodetermining step involves a 6π electrocyclization under both thermal and photoredox conditions.

Gut bacterial alginate degrading enzymes.

Alginates are abundant marine anionic polysaccharides consumed by humans. Thus, over the years some understanding has emerged about alginate utilization by human gut microbiota (HGM). However, insights have been obtained only recently at the molecular level with regard to structure and function of alginate degrading and metabolizing enzymes from HGM. Still, numerous studies report on effects of alginates on bacterial communities from digestive tracts of various, predominantly marine organisms feeding on alginate and some of the involved alginate lyases have been characterized. Other studies describe the beneficial impact on gut microbiota elicited by alginates in animal models, for example, high-fat-diet-fed mice addressing obesity or as feed supplements for livestock. Alginates are depolymerized by a ß-elimination reaction catalyzed by polysaccharide lyases (PLs) referred to as alginate lyases (ALs). The ALs are found in 15 of the 42 PL families categorized in the CAZy database. While genome mining has led to prediction of ALs encoded by bacteria of the HGM; currently, only four enzymes from this niche have been characterized biochemically and two crystal structures are reported. Alginates are composed of mannuronate (M) and guluronate (G) residues organized in M-, G-, and MG-blocks, which calls for ALs of complementary specificity to effectively depolymerize alginate to alginate oligosaccharides (AOSs) and monosaccharides. Typically, ALs of different PL families are encoded by genes arranged in clusters denoted as polysaccharide utilization loci. Currently, biochemical and structural analyses of marine bacterial ALs contribute to depicting the mode of action of predicted enzymes from bacteria of the HGM.

The European guideline on management of major bleeding and coagulopathy following trauma: sixth edition.

BACKGROUND: Severe trauma represents a major global public health burden and the management of post-traumatic bleeding continues to challenge healthcare systems around the world. Post-traumatic bleeding and associated traumatic coagulopathy remain leading causes of potentially preventable multiorgan failure and death if not diagnosed and managed in an appropriate and timely manner. This sixth edition of the European guideline on the management of major bleeding and coagulopathy following traumatic injury aims to advise clinicians who care for the bleeding trauma patient during the initial diagnostic and therapeutic phases of patient management. METHODS: The pan-European, multidisciplinary Task Force for Advanced Bleeding Care in Trauma included representatives from six European professional societies and convened to assess and update the previous version of this guideline using a structured, evidence-based consensus approach. Structured literature searches covered the period since the last edition of the guideline, but considered evidence cited previously. The format of this edition has been adjusted to reflect the trend towards concise guideline documents that cite only the highest-quality studies and most relevant literature rather than attempting to provide a comprehensive literature review to accompany each recommendation. RESULTS: This guideline comprises 39 clinical practice recommendations that follow an approximate temporal path for management of the bleeding trauma patient, with recommendations grouped behind key decision points. While approximately one-third of patients who have experienced severe trauma arrive in hospital in a coagulopathic state, a systematic diagnostic and therapeutic approach has been shown to reduce the number of preventable deaths attributable to traumatic injury. CONCLUSION: A multidisciplinary approach and adherence to evidence-based guidelines are pillars of best practice in the management of severely injured trauma patients. Further improvement in outcomes will be achieved by optimising and standardising trauma care in line with the available evidence across Europe and beyond.

Tuning alginate ß-lactoglobulin complex coacervation by modulating pH and temperature.

The use of biomolecules in food matrices and encapsulation systems is, as in other areas, moving towards greener solutions and a center piece here is the complex coacervation between natural anionic polysaccharides and proteins. Both alginate and ß-lactoglobulin (ß-Lg) are used in different sectors and have been shown to coacervate at pH < 5.2. Albeit with increased interest, complex coacervation has almost exclusively been studied from a macromolecular perspective, and described as an interaction based on charge-charge attraction. Here, we show that through changes in pH and temperature, alginate ß-Lg complex coacervation can be tuned to purpose. By detailed biophysical and chemical characterization of coacervation and coacervate particles, insights into the molecular interaction and effect of external factors are obtained. We find that carboxylate resonance stabilization causes a release of protons at pH < pKa,alginate and an uptake of protons at pH > pKa,alginate upon coacervation. Proton release and uptake were quantified at pH 2.65 and 4.00 by isothermal titration calorimetry to be 4 and 2 protons per ß-Lg molecule, respectively. By increasing the temperature to 65 °C, we discovered a secondary ß-Lg concentration dependent coacervation step, where the formed particles change into large assemblies driven by entropy. These findings bring new insights to complex coacervation and its applicability in microencapsulation and drug delivery.

Molecular insights into alginate ß-lactoglobulin A multivalencies-The foundation for their amorphous aggregates and coacervation.

For improved control of biomaterial property design, a better understanding of complex coacervation involving anionic polysaccharides and proteins is needed. Here, we address the initial steps in condensate formation of ß-lactoglobulin A (ß-LgA) with nine defined alginate oligosaccharides (AOSs) and describe their multivalent interactions in structural detail. Binding of AOSs containing four, five, or six uronic acid residues (UARs), either all mannuronate (M), all guluronate (G), or alternating M and G embodying the block structural components of alginates, was characterized by isothermal titration calorimetry, nuclear magnetic resonance spectroscopy (NMR), and molecular docking. ß-LgA was highly multivalent exhibiting binding stoichiometries decreasing from five to two AOSs with increasing degree of polymerization (DP) and similar affinities in the mid micromolar range. The different AOS binding sites on ß-LgA were identified by NMR chemical shift perturbation analyses and showed diverse compositions of charged, polar and hydrophobic residues. Distinct sites for the shorter AOSs merged to accommodate longer AOSs. The AOSs bound dynamically to ß-LgA, as concluded from saturation transfer difference and 1 H-ligand-targeted NMR analyses. Molecular docking using Glide within the Schrödinger suite 2016-1 revealed the orientation of AOSs to only vary slightly at the preferred ß-LgA binding site resulting in similar XP glide scores. The multivalency coupled with highly dynamic AOS binding with lack of confined conformations in the ß-LgA complexes may help explain the first steps toward disordered ß-LgA alginate coacervate structures.

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.

Unaided efficient transglutaminase cross-linking of whey proteins strongly impacts the formation and structure of protein alginate particles.

There is a dogma within whey protein modification, which dictates the necessity of pretreatment to enzymatic cross-linking of ß-lactoglobulin (ß-Lg). Here microbial transglutaminase (MTG) cross-linked whey proteins and ß-Lg effectively in 50 mM NaHCO3, pH 8.5, without pretreatment. Cross-linked ß-Lg spanned 18 to >240 kDa, where 6 of 9 glutamines reacted with 8 of 15 lysines. The initial isopeptide bond formation caused loss of ß-Lg native structure with t1/2 = 3 h, while the polymerization occurred with t1/2 = 10 h. Further, cross-linking effects on protein carbohydrate interaction have been overlooked, leaving a gap in understanding of these complex food matrices. Complexation with alginate showed that ß-Lg cross-linking decreased onset of particle formation, hydrodynamic diameter, stoichiometry (ß-Lg/alginate) and dissociation constant. The complexation was favored at higher temperatures (40 °C), suggesting that hydrophobic interactions were important. Thus, ß-Lg was cross-linked without pretreatment and the resulting polymers gave rise to altered complexation with alginate.

Simulated gastrointestinal digestion of protein alginate complexes: effects of whey protein cross-linking and the composition and degradation of alginate.

Alginate and whey protein are common additives in food production improving storage stability, texture and nutritional value. Alginate forms complexes with whey protein and inhibits proteolysis by pepsin and trypsin, but the influence of alginate protein complexation on digestion is poorly understood. This study shows that whey protein cross-linking by microbial transglutaminase dramatically decreased particle size (2-fold) and viscosity of alginate protein complexes. The INFOGEST in vitro simulated gastrointestinal digestion of whey protein was increased by cross-linking (16%) and suppressed by alginate, most pronounced with high mannuronic acid and least with high guluronic acid content. Sizes of alginate whey protein particles increased during gastric digestion, whereas for cross-linked whey protein complexes the size initially increased, but returned to their initial size at the end of gastric digestion. While alginate is not degraded by human enzymes, a few gut bacteria were recently found to encode lyases and other enzymes metabolizing alginate. Alginate lyase added to the intestinal phase enhanced digestion (9%) as controlled by alginate composition and enzyme specificity. Thus we provide evidence that use of hydrocolloids and processing of protein strongly influence digestion and should be considered when using food additives.

Characterization of a novel non-steroidal glucocorticoid receptor agonist optimized for topical treatment.

Glucocorticoids (GCs) are commonly used topical treatments for skin diseases but are associated with both local and systemic side effects. In this study, we describe a selective non-steroidal glucocorticoid receptor (GR) agonist for topical use, LEO 134310, which is rapidly deactivated in the blood resulting in low systemic exposure and a higher therapeutic index in the TPA-induced skin inflammation mouse model compared with betamethasone valerate (BMV) and clobetasol propionate (CP). Selectivity of LEO 134310 for GR was confirmed within a panel of nuclear receptors, including the mineralocorticoid receptor (MR), which has been associated with induction of skin atrophy. Topical treatment with LEO 134310 in minipigs did not result in any significant reduction in epidermal thickness in contrast to significant epidermal thinning induced by treatment with BMV and CP. Thus, the profile of LEO 134310 may potentially provide an effective and safer treatment option for skin diseases compared with currently used glucocorticoids.

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.

Lacticaseibacillus rhamnosus Impedes Growth of Listeria spp. in Cottage Cheese through Manganese Limitation.

Acidification and nutrient depletion by dairy starter cultures is often sufficient to prevent outgrowth of pathogens during post-processing of cultured dairy products. In the case of cottage cheese, however, the addition of cream dressing to the curd and subsequent cooling procedures can create environments that may be hospitable for the growth of Listeria monocytogenes. We report on a non-bacterio-cinogenic Lacticaseibacillus rhamnosus strain that severely limits the growth potential of L. monocytogenes in creamed cottage cheese. The main mechanism underlying Listeria spp. inhibition was found to be caused by depletion of manganese (Mn), thus through competitive exclusion of a trace element essential for the growth of many microorganisms. Growth of Streptococcus thermophilus and Lactococcus lactis that constitute the starter culture, on the other hand, were not influenced by reduced Mn levels. Addition of L. rhamnosus with Mn-based bioprotective properties during cottage cheese production therefore offers a solution to inhibit undesired bacteria in a bacteriocin-independent fashion.

Binding Sites for Oligosaccharide Repeats from Lactic Acid Bacteria Exopolysaccharides on Bovine ß-Lactoglobulin Identified by NMR Spectroscopy.

Lactic acid bacterial exopolysaccharides (EPS) are used in the food industry to improve the stability and rheological properties of fermented dairy products. ß-Lactoglobulin (BLG), the dominant whey protein in bovine milk, is well known to bind small molecules such as fatty acids, vitamins, and flavors, and to interact with neutral and anionic polysaccharides used in food and pharmaceuticals. While sparse data are available on the affinity of EPS-milk protein interactions, structural information on BLG-EPS complexes, including the EPS binding sites, is completely lacking. Here, binding sites on BLG variant A (BLGA), for oligosaccharides prepared by mild acid hydrolysis of two EPS produced by Streptococcus thermophilus LY03 and Lactobacillus delbrueckii ssp. bulgaricus CNRZ 1187, respectively, are identified by NMR spectroscopy and supplemented by isothermal titration calorimetry (ITC) and molecular docking of complexes. Evidence of two binding sites (site 1 and site 2) on the surface of BLGA is achieved for both oligosaccharides (LY03-OS and 1187-OS) through NMR chemical shift perturbations, revealing multivalency of BLGA for EPS. The affinities of LY03-OS and 1187-OS for BLGA gave K D values in the mM range obtained by both NMR (pH 2.65) and ITC (pH 4.0). Molecular docking suggested that the BLGA and EPS complexes depend on hydrogen bonds and hydrophobic interactions. The findings provide insights into how BLGA engages structurally different EPS-derived oligosaccharides, which may facilitate the design of BLG-EPS complexation, of relevance for formulation of dairy products and improve understanding of BLGA coacervation.

Impact of Alginate Mannuronic-Guluronic Acid Contents and pH on Protein Binding Capacity and Complex Size.

Alginates, serving as hydrocolloids in the food and pharma industries, form particles at pH < 4.5 with positively charged proteins, such as ß-lactoglobulin (ß-Lg). Alginates are linear anionic polysaccharides composed of 1,4-linked ß-d-mannuronate (M) and α-l-guluronate (G) residues. The impact of M and G contents and pH is investigated to correlate with the formation and size of ß-Lg alginate complexes under relevant ionic strength. It is concluded, using three alginates of M/G ratios 0.6, 1.1, and 1.8 and similar molecular mass, that ß-Lg binding capacity is higher at pH 4.0 than at pH 2.65 and for high M content. By contrast, the largest particles are obtained at pH 2.65 and with high G content. At pH 4.0 and 2.65, the stoichiometry was 28-48 and 3-10 ß-Lg molecules bound per alginate, respectively, increasing with higher M content. The findings will contribute to the design of formation of the desired alginate-protein particles in the acidic pH range.

Cytoplasmic Citrate Flux Modulates the Immune Stimulatory NKG2D Ligand MICA in Cancer Cells.

Immune surveillance of cancer cells is facilitated by the Natural Killer Group 2D (NKG2D) receptor expressed by different lymphocyte subsets. It recognizes NKG2D ligands that are rarely expressed on healthy cells, but upregulated by tumorigenesis, presenting a target for immunological clearance. The molecular mechanisms responsible for NKG2D ligand regulation remain complex. Here we report that cancer cell metabolism supports constitutive surface expression of the NKG2D ligand MHC class I chain-related proteins A (MICA). Knockout of the N-glycosylation gene N-acetylglucosaminyltransferase V (MGAT5) in HEK293 cells induced altered metabolism and continuous high MICA surface expression. MGAT5 knockout cells were used to examine the association of cell metabolism and MICA expression through genetic, pharmacological and metabolic assays. Findings were verified in cancer cell lines. Cells with constitutive high MICA expression showed enhanced spare respiratory capacity and elevated mitochondrial efflux of citrate, determined by extracellular flux analysis and metabolomics. MICA expression was reduced by inhibitors of mitochondrial function, FCCP and etomoxir e.g., and depended on conversion of citrate to acetyl-CoA and oxaloacetate by ATP citrate lyase, which was also observed in several cancer cell types. Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq) analysis revealed that upregulated MICA transcription was associated with an open chromatin structure at the MICA transcription start site. We identify mitochondria and cytoplasmic citrate as key regulators of constitutive MICA expression and we propose that metabolic reprogramming of certain cancer cells facilitates MICA expression and NKG2D-mediated immune recognition.

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.