Electrophysiological evaluation of spinal reflexes during epidural anesthesia in an experimental model.
ABSTRACT We assessed the effects of epidural anesthesia with bupivacaine in the rat by serial recordings of spinal reflexes. The H wave from plantar muscles after electrical stimulation of the sciatic nerve evaluates a large nerve fiber spinal reflex arch. The extensor reflex response recorded from quadriceps muscle after stimulation of the contralateral tibial nerve assesses a reflex arch with small fiber afferents. After epidural injection of 0.2 mL of bupivacaine (0.25%, 0.5%, and 1.0% solutions) at the L5-L6 vertebral space, nociceptive, H, and extensor reflex responses were abolished within 1-3 min. Duration of complete blockade lasted 20-80 min, increasing with the anesthetic concentration, and complete recovery occurred after an additional period of 30-40 min. The responses recovered to amplitudes similar to preanesthesia controls, indicating that there was no damage to the nervous system. This study shows that electrophysiological recording and quantitation of nerve reflex responses is a useful and accurate method to evaluate the efficacy of local anesthetic agents.
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ABSTRACT: We assessed the effect of a lipid emulsion of bupivacaine on prolonging peripheral nerve and epidural anesthetic blockade in the rat. The intensity and duration of motor and sensory blockade produced by a single injection of aqueous solution (BPV-as) and lipid emulsion (BPV-em) preparations of 0.5% bupivacaine were evaluated by electrophysiological methods. Both preparations induced complete, reversible motor and sensory blockade after injection. The latency time to the maximal blockade and the duration of anesthetic blockade were more prolonged for BPV-em than for BPV-as. The increase in duration of maximal blockade was 1.4 times for nerve and 1.3 times for epidural anesthesia. Histological evaluation of spinal roots and spinal cord sections did not show any abnormalities or differences between animals injected with BPV-as and those injected with BPV-em. Pharmacokinetic studies showed lower plasma peak concentration and a longer elimination half-life for BPV-em than for BPV-as. Thus, BPV-em prolongs the effects of local anesthetics, allows a similar degree of blockade, and reduces the systems toxic effects of anesthetics compared with BPV-as. IMPLICATIONS: We assessed a lipid emulsion containing bupivacaine for peripheral nerve and epidural anesthetic blockade in the rat. The emulsion allowed a complete blockade, while increasing the duration of the anesthetic effect (by 30%-40%), compared with the standard bupivacaine aqueous solution.Anesthesia & Analgesia 08/1999; 89(1):121-7. · 3.42 Impact Factor
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ABSTRACT: Previously, we have shown that transplants of olfactory bulb ensheathing cells promoted regeneration of transected dorsal roots into the spinal cord. In this study, we assessed the ability of regenerating axons to make functional connections in the cord. Dorsal roots L3 to L6 were sectioned close to their entrance into the spinal cord and reapposed after injecting a suspension of ensheathing cells into each dorsal root entry zone (Group G). Afferent regeneration into the cord and recovery of spinal reflexes were compared with animals that received no injection (Group S) or culture medium without cells (Group C). Electrophysiological tests, to measure nerve conduction and spinal reflexes (H response and withdrawal reflex) evoked by stimulation of afferents of the sciatic nerve, were performed. At 14 days after surgery, H response was found in only 1 of 7 rats of Group G, and withdrawal reflexes were absent from all animals. At 60 days, the H response reappeared in 7 of 10 rats of Group G, and 1 of 5 of each of Groups C and S. The withdrawal reflex recovered in 4 of 10 rats of Group G, but in none of Groups C and S. Immunohistochemical labeling for calcitonin gene-related peptide (CGRP) in rats of Group G showed immunoreactive fibers entering the dorsal horn from sectioned roots, although at lower density than in the contralateral side. In conclusion, transplanted ensheathing cells promoted central regeneration and functional reconnection of regenerating sensory afferents.Annals of Neurology 03/1999; 45(2):207-15. · 11.91 Impact Factor
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ABSTRACT: Solid lipid nanoparticles (SLNs), as a drug carrier, are a very attractive strategy for sustained and controlled drug release. In this study, we investigated the feasibility of SLNs to prolong the action of lidocaine for potential application in epidural anesthesia and analgesia. Lidocaine-loaded SLNs were prepared with different lipids, including monostearin (MS), glyceryl palmitostearate (GP), and stearic acid (SA). The morphology and crystallinity were characterized with transmission electron microscopy and powder x-ray diffraction. In vitro release studies were carried in phosphate buffer solution of pH 7.4 using cellulose dialysis membrane. The in vivo efficacy of epidural anesthesia was evaluated in rats. Lidocaine was successfully incorporated in SLNs prepared with MS, GP, and SA, respectively. The particle sizes of lidocaine-loaded SLNs were 143 to 388 nm with polydispersity index of 0.29 to 0.45. Powder x-ray diffraction analysis showed that lidocaine was mainly dispersed in SLNs in an amorphous state. The in vitro release within 48 hrs showed that lidocaine released from SLNs was 80% with MS SLNs, 69% with GP SLNs, and 89% with SA SLNs. The epidural efficacy was compared with that of aqueous lidocaine HCl. Single injection of lidocaine SLN suspension produced epidural block for more than 8 hrs with MS SLNs, 12 hrs with GP SLNs, and 4 hrs with SA SLNs. ]The same dose of lidocaine in aqueous solution lasted for less than 2 hrs. Solid lipid nanoparticles can be exploited as a promising drug carrier for extending the action of lidocaine.Regional anesthesia and pain medicine 03/2012; 37(2):159-65. · 4.16 Impact Factor