Onset Of Motor Blockade Research Articles

Pharmacokinetics of local anesthetics during plexus blocks.

A new model for the study of pharmacokinetics of local anesthetics is described which allows the separate determination of onset and recovery of sensory and motor blockade in peripheral (mantle) and central (core) bundles within nerve trunks. The data obtained with this model indicate that in man the sequence and pattern of both onset of and recovery from blockade differ from those predicted on the basis of available laboratory data. Results of this study indicate that in man, following the subclavian perivascular injection of 1 percent lidocaine with 1:200,000 epinephrine the onset of motor blockade precedes, or at least occurs simultaneously with, sensory blockade, 1st in the mantle bundles and then in the core bundles. Furthermore, significant motor blockade persists as long as, if not longer than, sensory blockade in both the mantle and the core fibers, but with recovery occurring 1st in the core bundles and last in the mantle bundles. The reason that motor onset precedes sensory onset is related to the fact that because of the somatotopic arrangement of fibers in a nerve bundle at the level of the trunks, motor fibers are located more peripherally than sensory fibers, and hence a local anesthetic injected perineurally will arrive at (and begin to block) motor fibers before it arrives at the more centrally located sensory fibers. The reason that significant motor blockade outlasts sensory blockade and that the block recedes in the hand before it recedes in the upper arm is presumably that, because of the intraneural vascular architecture, as the intraneural vessels move from periphery to core, branching and rebranching, the interface between blood vessels and nerve fibrils increases progressively. Thus after the establishment of complete blockade, there will be a greater uptake of local anesthetic in the central portions of the nerve than in the periphery. Therefore, the more central fibers, ie, the sensory fibers, recover first, followed by the more peripherally placed motor fibers.

EFFECTS OF EXTRADURAL BLOCK: COMPARISON OF THE PROPERTIES, CIRCULATORY EFFECTS AND PHARMACOKINETICS OF ETIDOCAINE AND BUPIVACAINE

Five healthy, unmedicated male volunteers, aged 19-25 yr, participated in a double-blind, crossover study. Each subject received, on separate occasions and via a catheter placed at L2, 1.5% etiodocaine HCl20 ml with adrenaline 5 mug/ml, or 0.75% bupivacaine HCl 20 ml with adrenaline 5 mug/ml for extradural analgesia. In addition, in order to calculate the absorption rate of the local anaesthetic agent, each subject received on two further occasions etidocaine HCl 75 mg and bupivacaine HCl 75 mg respectively by i.v. infusion, over a period of 10 min. Spread of sensory analgesia to four segments above and below the site of injection was faster with etidocaine (13 +/- 3 min) (mean +/- SD) than with bupivacaine (22 +/- 8 min). Two-segment regression occurred later for bupivacaine (260 +/- 57 min) than for etidocaine (180 +/- 96 min). Caudal spread of analgesia was more extensive with etidocaine than with bupivacaine. The onset of motor blockade tended to be faster with etidocaine (5.8 +/- 3.0 min), than with bupivacaine (10.0 +/- 3.5 min); regression of motor blockade by one unit was longer with etidocaine (306 +/- 103 min) than bupivacaine (238 +/- 75 min). Sudomotor block occurred earlier with etidocaine (4.0 +/- 2.1 min) than bupivacaine (13.7 +/- 4.8 min). Significant changes in cardiac stroke work and stroke volume occurred. For etidocaine these measurements remained below control values for 120-210 min after injection. The mean maximum arterial plasma concentration of etidocaine was 1.52 +/- 0.64 mug/ml, at 14 +/- 2 min and of bupivacaine was 1.35 +/- 0.63 mug/ml, achieved at 20 +/- 4 min. The systemic absorption of both drugs occurred in a biphasic pattern with a fast and slow half-life of 0.3 and approximately 8 h respectively.

Effectiveness of addition of neostigmine or dexamethasone to local anaesthetic in providing perioperative analgesia for brachial plexus block: A prospective, randomized, double blinded, controlled study

Various local anaesthetic agents are used for brachial plexus block.We compared effectiveness of addition of Dexamethasone versus Neostigmine to Lignocaine, adrenaline admixtures for Brachial plexus block in providing perioperative analgesia. Ninety patients were randomized in three groups and were received 24 ml of study drugs. The group A [Lignocaine with adrenaline (1.5%)], group B [Lignocaine with adrenaline (1.5%)] +500 microg Neostigmine, and group C (Lignocaine with adrenaline (1.5%) +4 mg Dexamethasone) for brachial plexus block through supraclavicular approach. The observed parameters were onset of analgesia, completion of sensory and motor blockade, Duration of analgesia, Surgeon's score, side effects, number of supplemental analgesics doses and Visual analogue scale (VAS) score for pain in 12 hour of post-operative period. Mean onset of analgesia 4.6+/-1.1 , 4.4 +/-0.8 , 3.8+/-1.8 mins in group A,B and C respectively and the Mean onset of motor blockade were 7.7+/- 2.0, 7.0+/-1.8, 6.0 +/- 2.1 mins in group A,B and C respectively. Similarly Mean Complete sensory block in 10.6 +/-3, 10.4+/-2.5, and 8.9+/-2.2 mins and Mean complete motor block in 17.3+/-4.3, 17.2 +/-4.0 and 14.7+/-3.5 mins in group A, B and C respectively were achieved. Duration of analgesia was 176.5+/-53.5, 225.7+/-53.3 and 454.2+/-110.7 mins in group A, B and C respectively. Duration of analgesia in group C was statistically significant in comparison with other groups. The number of mean analgesic requirement by group C (0.9+/-0.4) was significantly (p-0.005) lower. The mean VAS was significantly lower in group C in 12 hours post-operatively. The onsets of action, duration of analgesia were better in dexamethasone group and also need less number of rescue analgesics requirement.

PHANTOM SENSATIONS DURING SPINAL ANESTHESIA.

One hundred patients for elective surgical procedures were given tetracaine spinal anesthesia and observations were made in regard to time of injection, onset of motor blockade and limb position before and after blockade. Twenty-four patients experienced a painless phantom sensation which was directly related to the position of their limbs at the time of the motor blockade. Seventy-three patients were supine with outstretched limbs at the time of onset of motor blockade and did not experience phantoms. Three patients had subarachnoid sacral block, did not lose proprioceptive function and did not have phantom sensations.