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Biomedical subjects

J A Wildsmith

Publications and source records attributed to J A Wildsmith.

At least 91 records · Page 5Linked to original sources
PubMed1989

Extradural pressure following the injection of two volumes of bupivacaine.

We investigated the influence of the pressure generated by low lumbar extradural injection of bupivacaine on the development of block in a randomized double-blind study. Thirty patients (aged 17-66 yr) received one of two volumes of 0.75% bupivacaine. Group I (n = 15) received 10 ml (75 mg) and group II (n = 15) 15 ml (112.5 mg). Injection of the larger volume resulted in a greater pressure at the end of injection, but within 1 min this decayed to the same plateau pressure that was produced by the smaller volume. Mean maximum cephalad spread of block was the same in each group (group I, T9.5; group II, T8.4) and there was no correlation between individual level of block and maximum or plateau extradural pressure, or with patient characteristics.

Adult↗
PubMed1989

Structure-activity relationships in differential nerve block at high and low frequency stimulation.

We have examined the in vitro sensitivities of A, B and C fibres in rabbit vagus nerves to local anaesthetic block with a range of local anaesthetic drugs. The nerves were maintained at 37 degrees C and pH 7.4 using an electrolyte solution equilibrated with 5% carbon dioxide. A fibres were the most, and C fibres the least, sensitive to block at low frequency stimulation (0.0167 Hz). Equipotent concentrations of the various drugs blocked C fibres at approximately the same rate. Rate of A fibre block was related to physicochemical properties of individual drugs. Low pKa and high lipid solubility favoured block of A fibres before C, whereas the reverse was true for high pKa and low solubility. Absolute potency was related to lipid solubility, but each type of local anaesthetic drug in clinical use has a different inherent potency. With stimulation at high frequencies (20 and 40 Hz), C fibres were more sensitive to use-dependent block than A fibres; this effect was more marked with drugs containing an amide than an ester linkage. Molecular size and lipid solubility may inter-react to govern the ability to produce use dependent block. Agents which contain an amide linking group, have a high pKa and are of low lipid solubility, may be used to produce differential C fibre block.

Action Potentials↗
PubMed1988

Spinal anaesthesia.

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Anesthesia, Spinal↗
PubMed1988

Plasma prilocaine concentrations after three techniques of brachial plexus blockade.

Brachial plexus blockade (n = 30: 10 axillary, 10 perivascular subclavian, 10 interscalene) was performed on 28 patients, using 35 ml of 1.5% prilocaine in plain solution. Plasma prilocaine concentrations were measured at intervals over the following 60 min. There was no significant difference in the prilocaine concentrations between the three groups. One asymptomatic patient in the interscalene group had a peak prilocaine concentration greater than the accepted threshold for toxic symptoms.

Brachial Plexus↗
PubMed1988

Effect of dextrose concentration on the intrathecal spread of amethocaine.

Effects of solutions of 0.5% amethocaine, containing different concentrations of dextrose (0%, 1.25%, 2.5% and 5%) were studied after intrathecal injection. The cephalad extent of block was greater with all three dextrose-containing solutions (T6), compared with the isobaric solution which contained no dextrose (T11). The variability of maximum level of block within each group was similar (seven dermatomes), and the rate of onset to maximum extent of block was the same in all groups. The rate of onset to the T12 dermatome was more rapid in the patients who received solutions containing dextrose. The initial onset of effect of the solution containing 1.25% dextrose was more like that of the isobaric solution than of those containing higher concentrations of dextrose.

Adolescent↗
PubMed1988

Extradural block with bupivacaine: influence of dose, volume, concentration and patient characteristics.

In a randomized, double-blind study the influences of the characteristics of both solution (dose, volume, concentration) and patient (age, weight, height, body mass index) on the development of extradural blockade produced by a low lumbar injection of bupivacaine were investigated. Thirty patients aged between 20 and 50 yr received one of three solutions (groups I-III, respectively): 0.75% 10 ml (75 mg); 0.5% 15 ml (75 mg); 0.75% 15 ml (112.5 mg). A further 20 patients older than 50 yr received 0.75% bupivacaine 10 ml (group IV, n = 10) or 15 ml (group V, n = 10). The number of segments blocked at maximal extent of block was virtually the same in each group: group I (0.75% 10 ml) 13.3 (SD 1.4); group II (0.5% 15 ml) 14.1 (2.9); group III (0.75% 15 ml) 13.8 (2.2); group IV (0.75% 10 ml) 14.2 (2.1); group V (0.75% 15 ml) 16.7 (3.1). The larger dose of bupivacaine (112.5 mg) produced the fastest onset and longest duration of block. Onset and recovery intervals were similar with 0.75% and 0.5% solutions when administered at the same dose (75 mg in 10 ml or 15 ml). There was no correlation between the level of block and the age, weight and height of the patient. In patients who received 15-ml injections, there was a positive association between the upper level of block and body mass index.

Adult↗
PubMed1988

The effects of injected solution temperature on intravenous regional anaesthesia.

Ten healthy volunteers received three standard Bier's blocks. Prilocaine 0.5%, 40 ml was injected at a solution temperature of 0 degrees C, 22 degrees C or 37 degrees C. Recordings were made of sensory block, motor block, intravenous pressure, limb temperature and pain on injection. There were no differences between the three treatments in the rate of development or in the quality of block but there was a significant difference in the comfort of injection. Cold solutions caused most, and warm solutions least discomfort.

Anesthesia, Intravenous↗
PubMed1987

Differential nerve blockade: esters v. amides and the influence of pKa.

The in vitro sensitivities to local anaesthetic blockade of A, B and C fibres in rabbit vagus nerves were examined using a series of structurally similar amide agents, which varied in lipid solubility and anaesthetic potency. The actions of these drugs were compared with one another, and with those of a series of amino-ester local anaesthetics studied previously. The results demonstrated that A fibres are the most, and C fibres the least, sensitive to blockade by local anaesthetic agents. As with the ester drugs, equipotent concentrations of the amides blocked C fibres at approximately the same rate, but the absolute and relative rates of development of A fibre blockade were related to lipid solubility. As the latter increased, so did the rate of A fibre blockade. Combining the results of the two studies suggests that an agent of low lipid solubility and high pKa might be used to produce differential C fibre blockade. Comparison of the results obtained with the two different classes of drug indicates that the ester structure may have an inherently more potent action than the amide.

Action Potentials↗
PubMed1987

Acute beta-adrenoreceptor blockade and induced hypotension.

Thirty patients scheduled for major middle ear surgery and induced hypotension, with a trimetaphan/sodium nitroprusside infusion, were randomly allocated to receive a single oral dose of beta-adrenoreceptor antagonist 2 hours before surgery. In group 1 ten patients received metoprolol 50 mg, in group 2 ten patients received metoprolol 25 mg and in group 3 ten patients received oxprenolol 20 mg. There were ten controls for each group. The nitroprusside infusion rate was significantly reduced in groups 1 and 3. However, there was an unacceptably high incidence of profound bradycardia after induction of anaesthesia in those patients who had received beta-adrenoreceptor antagonists pre-operatively and this technique is not recommended for routine use.

Adolescent↗
PubMed1986

Plain bupivacaine: an unpredictable spinal anaesthetic agent.

Plain bupivacaine 0.5% or 0.75% was injected intrathecally in four groups of 10 patients. Group A received 0.75% bupivacaine 2.7 ml at L3/4, group B 0.5% bupivacaine 4 ml at L3/4, group C 0.75% bupivacaine 2.7 ml at L2/3 and group D 0.75% bupivacaine 2 ml at L3/4. A very wide range of height of block was found in each group and because of this there were few statistically significant differences between the groups. The mean height of anaesthetic blockade was significantly higher when 20 mg (group C) was injected compared with 15 mg (group D). Decreasing the volume of injection from 4 ml (group B) to 2.7 ml (group A) did not decrease this variability. By injecting at L2/3 spinal space (group C) the mean maximum level of anaesthesia (T7) was four segments higher than group A (T11) injected at L3/4, and this was reflected in a greater incidence of arterial hypotension.

Adult↗