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.

First Experience With Rectus Sheath Block for Postoperative Analgesia After Pancreas Transplant: A Retrospective Observational Study.

BACKGROUND: Standard of care for postoperative analgesia after pancreas transplant has been thoracic epidural analgesia (TEA). A high incidence of venous graft thrombosis necessitated a change to a more aggressive anticoagulation protocol. To minimize the risk of epidural hemorrhages, we changed from TEA to rectus sheath block (RSB) in 2017. METHODS: From June 2016 to December 2017, a total of 29 consecutive pancreas transplant recipients were included. Sixteen were treated with TEA and 13 were treated with RSB. In the TEA group, the catheter was inserted before induction of general anesthesia, and an epidural infusion was started intraoperatively. An ultrasound-guided RSB was performed bilaterally, and a bolus of local anesthetic was administered before an 18G catheter was inserted. The patients received intermittent local anesthetic boluses every 4 hours in addition to an intravenous patient-controlled analgesia with oxycodone. Both groups received oral acetaminophen and additional rescue opioids. RESULTS: The administered amount of intravenous morphine equivalents (MEQ) was not significantly different between the RSB and TEA groups. The median MEQ consumption per day during the stay at the surgical ward was 23 mg MEQ/d (interquartile range [IQR], 14-33 mg MEQ/d) in the TEA group compared with 19 mg MEQ/d (IQR, 14-32 mg MEQ/d) in the RSB group (P = .4). The duration of the pain catheters was significantly longer in the RSB group. We had no complications related to insertion, use, or removal of the RSB or the TEA catheters, and overall patient satisfaction and comfort was good. CONCLUSION: Compared with TEA, RSB was equally effective and safe for postoperative analgesia in heavily anticoagulated pancreas transplant patients.

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

A quantitative assessment of glutamate uptake into hippocampal synaptic terminals and astrocytes: new insights into a neuronal role for excitatory amino acid transporter 2 (EAAT2).

The relative distribution of the excitatory amino acid transporter 2 (EAAT2) between synaptic terminals and astroglia, and the importance of EAAT2 for the uptake into terminals is still unresolved. Here we have used antibodies to glutaraldehyde-fixed d-aspartate to identify electron microscopically the sites of d-aspartate accumulation in hippocampal slices. About 3/4 of all terminals in the stratum radiatum CA1 accumulated d-aspartate-immunoreactivity by an active dihydrokainate-sensitive mechanism which was absent in EAAT2 glutamate transporter knockout mice. These terminals were responsible for more than half of all d-aspartate uptake of external substrate in the slices. This is unexpected as EAAT2-immunoreactivity observed in intact brain tissue is mainly associated with astroglia. However, when examining synaptosomes and slice preparations where the extracellular space is larger than in perfusion fixed tissue, it was confirmed that most EAAT2 is in astroglia (about 80%). Neither d-aspartate uptake nor EAAT2 protein was detected in dendritic spines. About 6% of the EAAT2-immunoreactivity was detected in the plasma membrane of synaptic terminals (both within and outside of the synaptic cleft). Most of the remaining immunoreactivity (8%) was found in axons where it was distributed in a plasma membrane surface area several times larger than that of astroglia. This explains why the densities of neuronal EAAT2 are low despite high levels of mRNA in CA3 pyramidal cell bodies, but not why EAAT2 in terminals account for more than half of the uptake of exogenous substrate by hippocampal slice preparations. This and the relative amount of terminal versus glial uptake in the intact brain remain to be discovered.

The glutamate transporter EAAT4 in rat cerebellar Purkinje cells: a glutamate-gated chloride channel concentrated near the synapse in parts of the dendritic membrane facing astroglia.

Antibodies to an excitatory amino acid transporter (EAAT4) label a glycoprotein of approximately 65 kDa strongly in the cerebellum and weakly in the forebrain. Cross-linking of cerebellar proteins with bis(sulfosuccinimidyl) suberate before solubilization causes dimer bands of EAAT4 and both dimer and trimer bands of the other glutamate transporters GLAST (EAAT1) and GLT (EAAT2) to appear on immunoblots. In contrast to GLAST, GLT, and EAAC (EAAT3), EAAT4 is unevenly distributed in the cerebellar molecular layer, being strongly expressed in parasagittal zones. It is located in cerebellar Purkinje cells, and the highest concentrations are seen in ones expressing high levels of zebrin II (aldolase C). The labeling of Purkinje cell spines and thin dendrites is stronger than that of large diameter dendrites and cell bodies. EAAT4 is present at low concentrations in the synaptic membrane, but is highly enriched in the parts of the dendritic and spine membranes facing astrocytes (which express GLAST and GLT) compared with parts facing neuronal membranes, suggesting a functional relationship with glial glutamate transporters. The presence of EAAT4 in intracellular cisterns and multivesicular organelles may reflect turnover of transporter in the plasma membrane. The total Purkinje cell spine surface and the EAAT4 concentration were found to be 1.1 m2/cm3 and 0.2 mg/cm3, respectively, in the molecular layer, corresponding to 1800 molecules/microm2. The juxtasynaptic location of EAAT4 may explain electrophysiological observations predicting the presence of a neuronal glutamate transporter near the release site at a Purkinje cell spine synapse. EAAT4 may function as a combined transporter and inhibitory glutamate receptor.

Differential developmental expression of the two rat brain glutamate transporter proteins GLAST and GLT.

The extracellular concentration of the excitatory neurotransmitter glutamate is kept low by the action of glutamate transporters in the plasma membranes of both neurons and glial cells. These transporters may play important roles, not only in the adult brain, but also in the developing brain, as glutamate is thought to modulate the formation and elimination of synapses as well as neuronal migration, proliferation and apoptosis. Here we demonstrate the developmental changes in the expression of two glutamate transporters, GLAST and GLT, by quantitative immunoblotting and by light and electron microscopic immunocytochemistry. At birth, GLT is not detectable, but GLAST is present at significant concentrations both in the forebrain and in the cerebellum. GLT is first detected in the forebrain and cerebellum in the second and third week, respectively. Both transporters reach adult levels by postnatal week 5. The development of the total glutamate uptake activity in the forebrain, as determined by solubilization and reconstitution of the transporters in liposomes, parallels that of GLT, in agreement with the observation that GLT is the predominant transporter in the adult brain. The regional distributions of both GLAST and GLT in the tissue are similar in young and adult rats. Only GLAST is detectable in the external germinal layer of the cerebellar cortex. Electron microscopical investigation demonstrated GLAST and GLT exclusively in glial cells in young as well as in adult animals.

Brain glutamate transporter proteins form homomultimers.

Removal of excitatory amino acids from the extracellular fluid is essential for synaptic transmission and for avoiding excitotoxicity. The removal is accomplished by glutamate transporters located in the plasma membranes of both neurons and astroglia. The uptake system consists of several different transporter proteins that are carefully regulated, indicating more refined functions than simple transmitter inactivation. Here we show by chemical cross-linking, followed by electrophoresis and immunoblotting, that three rat brain glutamate transporter proteins (GLAST, GLT and EAAC) form homomultimers. The multimers exist not only in intact brain membranes but also after solubilization and after reconstitution in liposomes. Increasing the cross-linker concentration increased the immunoreactivity of the bands corresponding to trimers at the expense of the dimer and monomer bands. However, the immunoreactivities of the dimer bands did not disappear, indicating a mixture of dimers and trimers. GLT and GLAST do not complex with each other, but as demonstrated by double labeling post-embedding electron microscopic immunocytochemistry, they co-exist side by side in the same astrocytic cell membranes. The oligomers are held together noncovalently in vivo. In vitro, oxidation induces formation of covalent bonds (presumably -S-S-) between the subunits of the oligomers leading to the appearance of oligomer bands on SDS-polyacrylamide gel electrophoresis. Immunoprecipitation experiments suggest that GLT is the quantitatively dominant glutamate transporter in the brain. Radiation inactivation analysis gives a molecular target size of the functional complex corresponding to oligomeric structure. We postulate that the glutamate transporters operate as homomultimeric complexes.

The competitive transport inhibitor L-trans-pyrrolidine-2, 4-dicarboxylate triggers excitotoxicity in rat cortical neuron-astrocyte co-cultures via glutamate release rather than uptake inhibition.

We studied the early and late effects of L-trans-pyrrolidine-2,4-dicarboxylate (PDC), a competitive inhibitor of glutamate uptake with low affinity for glutamate receptors, in co-cultures of rat cortical neurons and glia expressing spontaneous excitatory amino acid (EAA) neurotransmission. At 100 or 200 microM, PDC induced different patterns of electrical changes: 100 microM prolonged tetrodotoxin-sensitive excitation triggered by synaptic glutamate release; 200 microM produced sustained, tetrodotoxin-insensitive and EAA-mediated neuronal depolarization, overwhelming synaptic activity. At 200 microM, but not at 100 microM, PDC caused rapid elevation of the glutamate concentration ([Glu]o) in the culture medium, resulting in NMDA receptor-mediated excitotoxic death of neurons 24 h later. The increase in [Glu]o was largely insensitive to tetrodotoxin, independent of extracellular Ca2+, and present also in astrocyte-pure cultures. By the use of glutamate transporters functionally reconstituted in liposomes, we showed directly that PDC activates carrier-mediated release of glutamate via heteroexchange. Glutamate release and delayed neurotoxicity in our cultures were suppressed if PDC was applied in a Na(+)-free medium containing Li+. However, replacement of Na+ with choline instead of Li+ did not result in an identical effect, suggesting that Li+ does not act simply as an external Na+ substitute. In conclusion, our data indicate that alteration of glutamate transport by PDC has excitotoxic consequences and that active release of glutamate rather than just uptake inhibition is responsible for the generation of neuronal injury.