Emmanuel Guntz

Effects of remifentanil on N-methyl-D-aspartate receptor : An electrophysiologic study in rat spinal cord

Background:Remifentanil hydrochloride contained in Ultiva® (GlaxoSmithKline, Genval, Belgium) has been incriminated in difficult postoperative pain management, promotion of hyperalgesia, and direct N-methyl-d-aspartate (NMDA) receptor activation, but the involved mechanisms have remained unclear. In the current study, the authors investigated the effects of remifentanil hydrochloride, with and without its vehicle, glycine, on the activation of NMDA receptors and the modulation of NMDA-induced current on neurons inside the lamina II from the dorsal horn of rat spinal cord. Methods:To test these effects, whole cell patch clamp recordings were conducted on acute rat lumbar spinal cord slices. Considering that both components of Ultiva® (remifentanil hydrochloride and glycine) could be involved in NMDA receptor activation, experiments were performed first with remifentanil hydrochloride, second with glycine, and third with the two components within Ultiva®. Results:Remifentanil hydrochloride does not induce any current, whereas 3 mm glycine induced a current that was abolished by the specific NMDA glutamate site antagonist d-2-amino-5-phosphonovalerate. Ultiva® (remifentanil hydrochloride with its vehicle, glycine) also evoked an inward current that was abolished by d-2-amino-5-phosphonovalerate and not significantly different from the glycine-induced current. Application of remifentanil hydrochloride potentiated the NMDA-induced inward current, and this potentiation was abolished by the &mgr;-opioid receptor antagonist naloxone. Conclusion:These results show that remifentanil hydrochloride does not directly activate NMDA receptors. The NMDA current recorded after application of Ultiva® is related to the presence of glycine. Induced NMDA current is potentiated by application of remifentanil hydrochloride through a pathway involving the &mgr;-opioid receptor.

Expression of adenosine A 2A receptors in the rat lumbar spinal cord and implications in the modulation of N-methyl-d-aspartate receptor currents.

BACKGROUND:The presence of A2A receptors in the dorsal horn of the spinal cord remains controversial. At this level, activation of N-methyl-d-aspartate (NMDA) receptors induces wind-up, which is clinically expressed as hyperalgesia. Inhibition of NMDA receptor currents after activation of A2A receptors has been shown in rat neostriatal neurons. In this study, we sought to establish the presence of adenosine A2A receptors in the lamina II of the rat lumbar dorsal horn neurons and investigated whether the activation of A2A receptors is able to modulate NMDA receptor currents. METHODS:Experiments were conducted in the rat lumbar spinal cord. The presence of adenosine A2A receptor transcripts inside the lumbar spinal cord is assessed with the reverse transcriptase polymerase chain reaction (RT-PCR) technique. Western blot experiments are performed at the same level. The RT-PCR technique is also performed specifically in the lamina II, and the presence of adenosine A2A receptor transcripts is assessed in neurons from the lamina II with the single-cell RT-PCR technique. The effect of adenosine A2A receptor activation on NMDA receptor currents is studied by the whole-cell configuration of the patch clamp technique. RESULTS:RT-PCR performed on the lumbar spinal cord revealed the presence of adenosine A2A receptor transcripts. Western blot experiments revealed the presence of A2A receptors in the lumbar spinal cord. RT-PCR performed on the substantia gelatinosa also revealed the presence of adenosine A2A receptor transcripts. Finally, single cell RT-PCR revealed the presence of adenosine A2A receptor transcripts in a sample of lamina II neurons. Patch clamp recordings showed an inhibition of NMDA currents during the application of a selective A2A agonist. CONCLUSIONS:These results demonstrate the presence of A2A receptor on neurons from the substantia gelatinosa of the rat lumbar dorsal horn and the inhibition of NMDA-induced currents by the application of a selective A2A receptor agonist. Therefore, A2A receptor ligands could modulate pain processing at the spinal cord level.

The radial nerve should be blocked before the ulnar nerve during a brachial plexus block at the humeral canal.

PurposeThe brachial plexus block through the humeral canal as described by Dupré is indicated in hand and forearm surgery. This block requires a multi-stimulation technique that emphasizes the necessity of a rigorous and safe technique. Nerve injury associated with regional anesthesia can entail significant morbidity for patients. Thus, we investigated the brachial block sequence in terms of unintended nerve stimulation as a surrogate of potential nerve injury.MethodsSixty patients were randomly allocated in two groups of 30. In Group I the radial nerve was blocked before the ulnar nerve. In Group II the ulnar nerve was blocked before the radial nerve. During the radial nerve approach we recorded, if present, an ulnar nerve response. During the ulnar nerve approach we recorded, if present, a radial nerve response.ResultsIn Group I while looking for the radial nerve, in 50% of the cases, an ulnar motor response was recorded. In Group II while looking for the ulnar nerve, a radial motor response was recorded in 10% of the cases.ConclusionOur results indicate that the radial nerve should be blocked before the ulnar nerve when performing a brachial plexus block at the humeral canal.RésuméObjectifLe blocage du plexus brachial au niveau du canal huméral, selon la technique de Dupré, est indiqué pour des opérations à la main et à l’avant-bras. Ce bloc nécessite une multi-stimulation, technique qui doit être faite avec rigueur et en toute sécurité. La lésion d’un nerf associée à l’anesthésie régionale peut donner lieu à une morbidité importante. La séquence du bloc brachial a donc été examinée sous l’angle de la stimulation involontaire d’un nerf, incident porteur d’une lésion potentielle à ce nerf.MéthodeSoixante patients ont été répartis aléatoirement en deux groupes de 30. Dans le groupe I, le nerf radial a été bloqué avant le nerf cubital. Dans le groupe II, nous avons fait l’inverse. Pendant l’approche du nerf radial, nous avons noté la présence ou non d’une réponse du nerf cubital. Pendant l’approche du nerf cubital, nous avons noté la réponse du nerf radial selon le cas.RésultatsDans le groupe I, pendant le blocage du nerf radial, nous avons noté une réponse motrice cubitale dans 50% des cas. Dans le groupe II, pendant le blocage du nerf cubital, nous avons noté une réponse motrice radiale dans 10% des cas.ConclusionNos résultats indiquent que le nerf radial doit être bloqué avant le nerf cubital quand nous réalisons un bloc du plexus brachial au niveau du canal huméral.

Sciatic nerve block in the popliteal fossa: description of a new medial approach

PurposeSciatic nerve blocks through lateral approaches in the popliteal fossa have been proposed. We describe a new medial approach to the sciatic nerve at this level.MethodsAfter an anatomical study on six cadavers, we performed sciatic nerve blocks on 20 patients. A 100-mm insulated needle and a nerve stimulator were used; 20 mL of lidocaine 1.5% with epinephrine were injected.ResultsPatients lied in the supine position, the thigh flexed, abducted and rotated externally (30° in all directions). The leg was flexed at 130°. In this position, above the adductor tubercle, a depression known as Jobert’s fossa is palpated. Through this groove, a medial approach to the sciatic nerve at the level of the popliteal fossa is possible. The mean distance between the adductor tubercle and the puncture site is 6.18 cm (range 4–8 cm) and the mean distance between the skin and the sciatic nerve is 6.62 cm (range 4–9 cm). Mean time to perform the block was 100 sec (range 55–165 sec). Complete motor blockade was obtained after a mean time of 30 min (range 5–60 min) inside the common peroneal nerve area and 43 min (range 15–75 min) inside the tibial nerve area. Motor block was complete in 17 patients and sensory block in 18 patients. No vessel puncture was observed.ConclusionWe describe a new medial approach to the sciatic nerve in the popliteal fossa. More studies will be required to demonstrate the technique is effective and safe.RésuméObjectifDes blocs du nerf sciatique par des approches latérales du creux poplité ont été proposés. Nous décrivons une nouvelle approche médiale du nerfsciatique à ce niveau.MéthodeAprès une étude anatomique sur six cadavres, nous avons réalisé des blocs du nerfsciatique sur 20 patients. Une aiguille isolée de 100 mm et un neurostimulateur ont été utilisés ; 20 mL de lidocaïne à 1,5% avec épinéphrine ont été injectés.RésultatsLes patients étaient étendus décubitus dorsal, la cuisse fléchie, en abduction et en rotation vers l’extérieur (de 30° dans toutes les directions). La jambe était fléchie à 130°. Dans cette position, une dépression connue sous le nom de fosse de Jobert est palpée au-dessus du tubercule de l’adducteur. Par ce sillon, une approche médiale du nerf sciatique est possible au niveau du creux poplité. La distance moyenne entre le tubercule de l’adducteur et le site de ponction est de 6,18 cm (limites 4–8 cm) et la distance moyenne entre la peau et le nerfsciatique est de 6,62 cm (limites 4–9 cm). Le temps moyen nécessaire pour réaliser le bloc a été de 100 sec (limites 55–165 sec). Le blocage moteur complet a été obtenu après un temps moyen de 30 min (limites 5–60 min) dans la zone du nerf sciatique poplité externe et de 43 min (limites 15–75 min) dans la zone du nerf tibial. Le bloc moteur a été complet chez 17 patients et le bloc sensitifchez 18 patients. Aucune ponction vasculaire n’a été observée.ConclusionNous décrivons une nouvelle approche médiale du nerf sciatique dans le creux poplité. Il reste à démontrer l’efficacité et la sécurité de la technique.

Totally retroperitoneal laparoscopic aortobifemoral bypass

Abstract The classic procedure for aortobifemoral bypass is open surgery. Since the first totally laparoscopic aortobifemoral bypass reported in 1997 by Yves-Marie Dion, laparoscopy has been accepted by several authors as a possible minimally invasive alternative for aorto-iliac occlusive disease. The transperitoneal left retrocolic and retrorenal ways are generally used. The totally retroperitoneal laparoscopic procedure has been described as an alternative to the transperitoneal approach. We report here a totally laparoscopic retroperitoneal approach to performing aortobifemoral bypass. This approach was proposed to a 51-year-old man with aorto-iliac occlusive disease. There was no indication for endovascular revascularization. The patient suffered from 10 metres of bilateral intermittent claudication and lower limb ulcers. During the surgical procedure our patient was placed in a 30-degree right lateral decubitus position. The optical system was first placed in an intra-abdominal position to check the positioning of the trocars in the left retroperitoneal space. The dissection of the retroperitoneal space was performed by CO2 insufflation and by blunt dissection using laparoscopic forceps. The infrarenal aorta was exposed and clamped by laparoscopic clamps. A bifurcated graft was sutured on the left-hand side of the aorta by a running suture. Both prosthetic limbs were tunnelized retroperitoneally to the groin under optical control. The femoral anastomoses were performed by classic open surgery.

Spinal prilocaine for same-day surgery: the importance of equipotent doses

To the Editor, We read with interest both the article published by Aguirre et al. regarding the comparison of intrathecal 2% hyperbaric prilocaine with ropivacaine for patients undergoing knee arthroscopy and the following discussion of Manassero et al. We believe that this exchange of opinions highlights the importance of administering doses of local anesthetics tailored to a particular clinical setting. The increasing volume of ambulatory surgery has recently led to more research on short-acting and intermediate-acting local anesthetics. Clinicians can now choose between anesthetics to fine-tune spinal anesthesia according to the length of the surgery. In regard to this concept, the dose of spinally administered hyperbaric prilocaine must be precisely defined. Some studies have compared various arbitrarily chosen doses of prilocaine with other local anesthetics in various clinical settings without always taking into account the equipotent doses of these anesthetics. Hyperbaric prilocaine is an intermediate-acting local anesthetic. Increasing the dose prolongs the duration of sensory and motor block. High doses provide blocks whose durations are comparable to those obtained with low doses of long-acting local anesthetics such as ropivacaine or bupivacaine, but they could induce adverse effects. Kreutziger et al. showed that 60 mg of hyperbaric prilocaine caused urinary retention in 23% of patients. On the contrary, decreasing the dose of hyperbaric prilocaine shortens the duration of the sensory and motor blocks but may lead to block failure depending on the desired sensory block level. In our previously published study, we determined the effective doses (ED50 and ED90) of intrathecal hyperbaric prilocaine for patients undergoing ambulatory knee arthroscopy. The minimum effective dose for patients undergoing knee arthroscopy (ED50) of hyperbaric 2% prilocaine was 28.9 mg, whereas the ED90 was 38.5 mg. In our study, all patients met the discharge criteria after 205 min and could spontaneously urinate. Moreover, the regression model we employed for statistical analysis suggested that 50 mg was the optimal clinical dose for knee arthroscopy. Indeed, with doses\50 mg, the patient could be exposed to block failure. Larger doses provided no gain in terms of successful spinal anesthesia and increased the side effects. The comparison of local anesthetics in particular clinical settings should be performed using equipotent doses. Thus, for some of the earlier local anesthetics with a new formulation (e.g., hyperbaric prilocaine and chloroprocaine), ED90 must be known and used.