Motor block

Another clinical consideration is the abiUty of local anesthetic agents to effect differential blockade of sensory and motor fibers. In surgical procedures such as obstetrics or postoperative pain rehef, an agent which produces profound sensory block accompanied by minimal motor block is desirable. On the other hand some procedures such as limb surgery require both deep sensory and motor blockade. In clinical practice, bupivacaine ( 22,... 

R = / -C H ), in low doses, exhibits the former behavior and is used primarily as an extradural agent in obstetrics. The lowest effective extradural concentration of etidocaine (21, X = CH, R = R = 2H, R = / -C H ), however, shows both adequate sensory and profound motor blockade so that it is useful in surgical situations where maximum neuromuscular blockade is necessary. In an isolated nerve preparation, bupivacaine blocks unmyelinated C fibers which are mainly responsible for pain perception at a much greater extent than the myelinated A fibers which carry motor impulses. It is postulated that absorption of bupivacaine by the vasculature at the site of injection, combined with the slow diffusion of this agent, results in an insufficient amount of the drug penetrating the large A fibers to cause motor conduction blockade. Clinically, motor block can be observed in some procedures. 

Motor Blocks. Automobile and tmck motors prepared to varying degrees of quality constitute a grade of scrap called motor blocks. The higher quality grades are stripped blocks from which most of the steel and nonferrous and nonmetaUic parts are removed and the blocks are broken to cupola size. Degreasing the scrap further improves its quality. 

Prolongation of spinal anesthesia IV The addition of 2-5 mg added to the anesthetic solution increases the duration of motor block by as much as 50% without an increase in the incidence of complications such as nausea, vomiting, or blood pressure disturbances. 

Bupivacaine is an amide compound with a duration of nerve blocking effect of around 3 hours. It is about four times more potent than lidocaine (lignocaine) and has an intermediate-to-slow onset of action. Bupivacaine is prepared as the hydrochloride salt in aqueous solutions in concentrations of 0.25%, 0.50%, and 0.75%. The incidence of motor block increases with increasing concentration. High doses of bupivacaine are associated with cardiac toxicity. Particular care must be exercised to avoid inadvertent overdosage or when the drug is administered to patients taking concurrent cardioactive medication. 

When used for spinal anaesthesia, 0.75% ropivacaine produces less intense sensory and motor block than 0.5% bupivacaine. It is suitable for regional, spinal and epidural block but not for regional intravenous anaesthesia. The addition of adrenaline (epinephrine) does not prolong the duration of anaesthesia in brachial plexus or epidural block. Ropivacaine is indistinguishable from bupivacaine when used in obstetric anaesthesia. Its direct myocardial toxicity is somewhat less than that of bupivacaine. 

Clinical use Etidocaine in combination with adrenaline is employed for infiltration anesthesia using solutions of 0.5% and peripheral nerve block at 0.5 and 1.0 % with a duration of 3 to 12 h (Tetzlaff, 2000). Epidural anesthesia is achieved with 1.0 to 1.5 % solutions with a duration of 3 to 5 h. Due to a profound motor block sometimes associated with unsatisfactory sensory block etidocaine is disadvantegous compared to bupivacaine. 

Clinical use Mepivacaine has been employed for all types of infiltration and conduction nerve block anesthesia using solutions of 1.0 and 1.5 % lasting for 1.5 to 3 h. Epidural anesthesia with 2.0 % mepivacaine has a rapid onset with a dense motor block. Hyperbaric solutions of mepivacaine have also been used for spinal anesthesia (Tetzlaff, 2000). Mepivacaine has been used for topical applications, but other LA such as lidocaine are more effective. 

Molybdenum disulfide is dispersed in greases and oils for lubrication in volatile carriers it is used to form dry coatings of lubricant. Sodium molybdate is an especially effective corrosion inhibitor on aluminum surfaces and is dissolved in cooling solutions to protect aluminum motor blocks in automobiles. 

Feldman HS, Covino BG (1988) Comparative motor-blocking effects of bupivacaine and ropivacaine, a new amino amide local anesthetic, in the rat and dog. Anesth Analg 67 1047-1052... 

In a study in 60 anesthetized children undergoing minor subumbilical surgery caudal blocks, 0.2% ropivacaine, 0.25% racemic bupivacaine, and 0.25% levobupivacaine (all 1 ml/kg) were compared (81). All the blocks were successful in terms of intraoperative and early postoperative analgesia. Ropivacaine, but not levobupivacaine, was associated with less motor block during the first postoperative hour compared with racemic bupivacaine. However, the lower concentration of ropivacaine will have biased this result. 

Prolonged profonnd motor block occnrred in two patients using patient-controUed epidnral analgesia with 0.1% ropivacaine subseqnent to spinal bnpivacaine for cesarean section (136). One of them developed pressnre sores on both heels. The authors hjq)othesized that epidural ropivacaine may interact with intrathecal bnpivacaine to prolong its effects and advised cantion when this combination is used, as unexpected motor block can ensne. 

Because of bupivacaine s longer half-life and greater tendency toward sensory than motor block it is commonly used epidurally during labor. This is in... 

Mepirzapin mirtazapine. mepitiostane [inn, jan] (S i0364) is a steroid with anabolic and antioestrogen activity. It has been used as an oral ANTICANCER AGENT for breast cancer, mepivacaine [ban. inn] (meplvacalne hydrochloride [usan] Carbocaine Polocaine Scandonest ) is an ester series LOCAL ANAESTHETIC with a rapid onset and intermediate duration of action. It is used by injection for infiltration, dental, regional and epidural pain relief and motor block, mepivacaine hydrochioride mepivacaine. mepixanox [inn] is a cm stimulant and respiratory... 

Injection of a local anesthetic into or around individual peripheral nerves or nerve plexuses produces even greater areas of anesthesia than do the techniques described above. Blockade of mixed peripheral nerves and nerve plexuses also usually anesthetizes somatic motor nerves, producing skeletal muscle relaxation, which is essential for some surgical procedures. The areas of sensory and motor block usually start several centimeters distal to the site of injection. Brachial plexus blocks are particularly useful for procedures on the upper extremity and shoulder. Intercostal nerve blocks are effective for anesthesia and relaxation of the anterior abdominal wall. Cervical plexus block is appropriate for surgery of the neck. Sciatic and femoral nerve blocks are useful for surgery distal to the knee. Other useful nerve blocks prior to surgical procedures include blocks of individual nerves at the wrist and at the ankle, blocks of individual nerves such as the median or ulnar at the elbow, and blocks of sensory cranial nerves. 

It is generally employed in solution form either alone or in eombination with adrenaline (a vasodilator). It exhibits upto 95% ability to cause plasma protein binding. Beeause it exerts a minimal nerve motor block, hence it is specifically suitable for some surgieal operations. The drug is largely metabolized in the liver and its metabolites are chiefly exereted in the urine. 

Fig. 3.8 Rotating sample cell used for difference Raman spectroscopy 7, motor 2, motor block 3, side parts 4, motor axis 5, set screw 6, kinematic mount 7, x-y precision ball glider 8, adjustment screw 9, divided liquid cell for difference Raman spectroscopy 70, axis for trigger wheel 77, trigger wheel 72, trigger hole 13, bar 14, optoelectronic array consisting of a photodiode and transistor [320]...

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