Spread of local anesthetic solutions in the thoracic epidural space

The segmental spread of thoracic epidural analgesia was measured in 14 patients scheduled for elective surgery with ages ranging from 35 to 80 years. Epidural puncture was performed in the seventh or eighth thoracic intervertebral space using 17 gauge Tuohy needle with the patient in the left lateral position. The epidural space was identified using "loss of resistance technique". With the bevel of the needle pointing towards the head, 7-10 ml of 2% mepivacaine was injected at the rate of 1 ml.sec-1. Fifteen minutes after injection of anesthetic, the spinal segments anesthetized were determined by absence of cold sensation. A statistically significant correlation was found between age and a segmental dose (ml.seg-1) (r = -0.72), and between age and a segmental dose corrected by height (ml.seg-1.m-1) (r = -0.65).     

Epinephrine, magnesium, and dental local anesthetic solutions.

Plasma levels of magnesium were unaffected by the inclusion of epinephrine in lidocaine dental local anesthetic solutions in patients having third molar surgery under general anesthesia.     

The relationship between pH and concentrations of antioxidants and vasoconstrictors in local anesthetic solutions.

pH affects the efficacy of local anesthetics by determining the percentage of the lipid-soluble base form of the anesthetic available for diffusion and penetration of the nerve sheath. The purpose of this study was to determine the relationship between pH and the concentrations of antioxidant and vasoconstrictor in dental local anesthetic solutions over real-time and after accelerated aging. Several batches of lidocaine and mepivacaine with vasoconstrictors were tested. Results showed that, immediately upon receipt from the manufacturers, three batches were below the USP pH limit (pH 3.3), and two batches contained less than the minimum limit of vasoconstrictors (90%). Real-time tests on batches that were within normal limits revealed that solutions were stable past 4 yr. Accelerated aging tests revealed a strong correlation between a decrease in pH and loss of antioxidants and vasoconstrictors. In conclusion, a quality batch of local anesthetic should remain efficacious long past the manufacturer's stated shelf life; a batch that is less than optimal, or one that is exposed to environmental stresses, will degrade rapidly, and efficacy may be affected by decreases in pH and loss of vasoconstrictor. pH may be an inexpensive, readily available screening test for efficacy of local anesthetics.     

The optimum initial pediatric epidural bolus: a comparison of four local anesthetic solutions

BACKGROUND: There is no consensus on the concentration or type of local anesthetic used for initiation of epidural anesthesia. The aim of this randomized, double-blind, controlled trial was to compare the clinical effectiveness of epidural administration of both levobupivacaine and bupivacaine in 0.2% and 0.25% concentrations in pediatric patients undergoing abdominal and urological surgery. METHODS: One hundred and forty-one children scheduled for lower abdominal and urological surgery were randomized to receive 0.4-0.6 ml.kg(-1) epidural, 0.25% bupivacaine, 0.2% bupivacaine, 0.25% levobupivacaine or 0.2% levobupivacaine. Initial epidural volumes, onset times; hemodynamic consequences, postoperative pain scores and degree of residual postoperative motor block were all recorded. RESULTS: There were no significant differences in the proportion of children with effective analgesia after incision [0.20% bupivacaine 97%, 0.25% bupivacaine 94%, 0.20% levobupivacaine 91%, 0.25% levobupivacaine 92% (P=0.73)] when a median volume of 0.55 ml.kg(-1) was used. There was no association between the volume used for thoracic, lumbar, or sacral epidural anesthesia and the effectiveness of the agents used. There was a significantly greater incidence of pain on awakening with the 0.2% solutions compared with the 0.25% solutions, but no differences in the incidence of residual motor block between groups. CONCLUSIONS: While there is no difference in the proportion of effective surgical anesthesia, the lower incidence of pain and distress with the 0.25% solutions suggests that this concentration has clinical advantages over the 0.2% solutions for pediatric epidural anesthesia.     

Essentials of local anesthetic pharmacology

It is impossible to provide effective dental care without the use of local anesthetics. This drug class has an impressive history of safety and efficacy, but all local anesthetics have the potential to produce significant toxicity if used carelessly. The purpose of this review is to update the practitioner on issues regarding the basic pharmacology and clinical use of local anesthetic formulations.     

Knee arthroscopy using local anesthetic

The purpose of this study was to examine the effectiveness and safety of local anesthetics (a mixture of lidocaine and bupivacaine) in knee arthroscopy. Local anesthetic agents were shown to be effective and safe, based on chart review and measurement of blood levels of the anesthetic drugs.     

Bilateral intravenous regional anesthesia: a new method to test additives to local anesthetic solutions

BACKGROUND: Ketorolac, when added to lidocaine, has been shown to reduce early tourniquet pain during intravenous regional anesthesia (i.v.RA) in patients. Although the effectiveness of ropivacaine 0.2% for i.v.RA is equal to that of lidocaine 0.5% but significantly reduces central nervous system side effects after release of the tourniquet, it provides no advantage with regard to tourniquet tolerance times. Simultaneous bilateral i.v.RA with ropivacaine 0.2% was used to test the hypothesis that ketorolac modifies tourniquet tolerance and to test whether drug combinations can be evaluated in one study session. METHODS: Ten healthy, unsedated volunteers received 30 ml of ropivacaine 0.2% in each upper arm with 2 ml of normal saline in one arm and 30 mg of ketorolac in the contralateral arm for i.v.RA. Both proximal tourniquets remained inflated for 30 min, followed by inflation of the distal tourniquets and release of the proximal ones. Verbal numeric scores for tourniquet pain were recorded for both extremities. Central nervous system side effects were graded after release of each distal tourniquet. RESULTS: There was no difference between the two upper extremities with regard to surgical anesthesia and tourniquet tolerance. Total tourniquet tolerance was a median of 58.5 min (range, 45-90 min) and 60.5 min (39-79 min) in the normal saline and ketorolac groups, respectively. After release of the distal tourniquets, 5 of 10 volunteers experienced mild dizziness. CONCLUSIONS: The addition of ketorolac to ropivacaine does not improve tourniquet tolerance. Minimal central nervous system side effects after tourniquet release suggest that a total of 60 ml ropivacaine 0.2% for bilateral i.v.RA is a useful model for comparison of i.v.RA drug combinations.     

Diffusional delay in local anesthetic block in vitro

The diffusion of lidocaine to myelinated and unmyelinated axons was compared on individual afferent fibers of rabbit vagus nerve. The criterion consisted of the time required for more than 95% completion of the asymptotic increase in impulse conduction time produced by a weak, nonblocking concentration of lidocaine. Measurements on sheathed and desheathed nerves for both myelinated and unmyelinated axons detected an apparent but statistically not significant diffusional lag at the perineurial sheath, averaging four minutes in this model; there was no significant difference in the mean time for attainment of criterion in myelinated and unmyelinated axons, which averaged an additional 13 min in both types of fiber. From these observations the authors conclude that lidocaine diffused as readily through the nodal gap to the excitable membrane of the myelinated fiber as through the Schwann cell mesaxon to the unmyelinated fiber. Thus differential diffusion within a nerve seems unlikely to be a contributing factor to clinical differential block.