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Biomedical subjects

C A Shanks

Publications and source records attributed to C A Shanks.

At least 37 records · Page 2Linked to original sources
PubMed1992

Neuromuscular contributions in eight anaesthesia journals.

Entries in the index issues of eight English-language anaesthesia journals were examined for the years 1950-1990, noting the number of original articles, reviews and editorials. Those which included topics involving neuromuscular blockade were examined in greater detail; these averaged almost one-tenth of the annual totals, despite its eightfold increase over the four decades. During the eighties the strongest research interest involved atracurium, pancuronium, succinylcholine, tubocurarine, and vecuronium, but the share for the long-acting agents was waning by 1990.

Anesthesiology↗
PubMed1992

Minimal compartmental model of circulatory mixing of indocyanine green.

A model of indocyanine green (ICG) disposition from the moment of its injection in blood was developed. ICG disposition was characterized in five dogs deeply anesthetized with halothane, which decreased cardiac output and prolonged intravascular mixing. After ICG injection into the right atrium, femoral arterial blood samples were collected every 3 s for the 1st min and less frequently to 20 min. ICG concentrations were measured by high-performance liquid chromatography and modeled with SAAM 30.1. A fully identifiable recirculatory compartmental model with time delays was used to describe ICG disposition. The central blood volume averaged 23.4 ml/kg, and total blood volume averaged 78.9 ml/kg. Fifty-three percent of the cardiac output flowed through 14% of the peripheral blood volume while the remaining 47% flowed through 86% of the peripheral volume. This new model is isomorphic with a parallel channel, lumped-parameter circulation model and provides more information than stochastic, noncompartmental recirculatory pharmacokinetic techniques. This intravascular mixing model can be applied to determine the contribution of the circulation to drug distribution.

Analysis of Variance↗
PubMed1990

Managing journal references with JREF, an IBM-compatible program to simplify manuscript preparation.

JREF is a program which stores, manages and converts journal references. It is intended for the writer of articles and reviews, to simplify the task of keeping card indexes. Entries can be made from downloaded literature searches or from the keyboard. When writing, selections are made from the archival files, for conversion into the specific style of the chosen Journal. All files are ASCII text, accessible to most word processing programs. Once the accuracy of entries has been confirmed, these can be transformed into a perfectly punctuated bibliography.

Abstracting and Indexing↗
PubMed1989

Dose-response relationships of doxacurium chloride in humans during anesthesia with nitrous oxide and fentanyl, enflurane, isoflurane, or halothane.

In a two-part study, the dose-response relationships of doxacurium chloride (BW A938U) were evaluated during general anesthesia maintained with commonly used anesthetic techniques. In part 1, cumulative dose-response methodology was used to establish the ED95 of doxacurium in 36 patients receiving 70% nitrous oxide and fentanyl, or 50% nitrous oxide and either 1.26% enflurane, 0.84% isoflurane, or 0.57% halothane anesthesia. Mechanomyographic response to train-of-four stimulation was used to monitor neuromuscular blockade. The peak effect of doxacurium following each 5 micrograms/kg incremental dose was noted and a log-probit dose-response curve was constructed for each individual patient. The median ED50s were 11 micrograms/kg, 6 micrograms/kg, 8 micrograms/kg, and 8 micrograms/kg for patients receiving fentanyl, enflurane, isoflurane, or halothane anesthesia, respectively. The median ED95s were 24 micrograms/kg, 14 micrograms/kg, 16 micrograms/kg, and 19 micrograms/kg for patients receiving fentanyl, enflurane, isoflurane, and halothane anesthesia, respectively. In part 2, 72 additional patients received a rapid single injection of the ED95 (n = 36) or 2 X ED95 (n = 36) of doxacurium appropriate for the administered anesthetic as estimated from part one of the study. Peak effects of the ED95 given as single injections correlated well with the results in part 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Mivacurium-induced neuromuscular blockade following single bolus doses and with continuous infusion during either balanced or enflurane anesthesia.

Mivacurium chloride (BW B1090U) was administered to 72 patients during their elective surgery. The eight groups (nine subjects per cell) in the 2 x 2 x 2 study design differed in three factors: the size of the mivacurium bolus dose administered, whether or not this dose was followed by an infusion of mivacurium, and in the technique used for the maintenance of anesthesia. Four groups received a single bolus dose of mivacurium, 0.15 mg/kg, and the remaining four groups received mivacurium, 0.25 mg/kg, administered iv in 15 s. Precisely 2 min later, tracheal intubation was attempted. Conditions were judged to be good or excellent on most occasions, but intubation was not possible for two of the patients in the low-dose and one in the high-dose groups. Four groups, two at each bolus dose, received no additional mivacurium: there was a dose-dependent decrease in the rate of spontaneous recovery following the bolus dose. The other subdivision of groups was the use of either barbiturate-nitrous oxide-narcotic (balanced) anesthesia, or enflurane-nitrous oxide anesthesia; the anesthetic technique did not affect the pattern of spontaneous recovery from either bolus dose. Four groups, again two at each bolus dose, subsequently received an infusion of mivacurium, adjusted to depress the twitch response by approximately 95%. Infusion rates averaged 6.0 micrograms.kg-1.min-1 in the groups receiving balanced anesthesia and 4.2 micrograms.kg-1.min-1 for those receiving enflurane anesthesia. Recovery following administration by infusion was slower than that observed following a bolus dose of mivacurium, 0.15 mg/kg but did not differ between the anesthetic groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Simulating the time-course of clinical paralysis.

This computer program depicts the concentration-time curves for the nondepolarizing neuromuscular blocking agents. It simulates their administration by single and multiple iv injections, and with continuous infusion, alone and in combination. It provides the plasma concentrations related to 75% and 25% depression of the twitch response, using these to calculate clinically useful pharmacodynamic values, such as the duration of surgical relaxation, and the recovery index. These simulations allow the user to contrast the time-course of relaxation to be expected with various dosage regimens.

Atracurium↗
PubMed1988

Developmental neurophysiology of mammalian peripheral nerves and age-related differential sensitivity to local anaesthetic.

Using an in vitro nerve preparation, we have studied the relative electrophysiological properties of myelinated and unmyelinated nerve fibres in the vagus nerve of 1-, 9- and 36-month-old rabbits and their sensitivity to local anaesthetic. The baseline (values before infusion of local anaesthetic) mean amplitude and conduction velocity (CV) of the compound action potential (APc) were recorded and the nerve was exposed to a range of concentrations (0.5-4.0 mmol litre-1) of lignocaine for periods sufficient to attain equilibrium block. There was an increase in the amplitude of the A fibre elevation from the 1-month to the 9- and 36-month-old rabbits. The CV of the A and B fibres increased significantly with age, while the CV of the C fibres did not change. The ED50 values of lignocaine for reduction of the A fibre elevation in the 1-, 9- and 36-month-old rabbits were 0.66, 0.94 and 0.85 mmol litre-1, respectively. The respective values for the B fibres were 0.74, 1.21 and 0.82 mmol litre-1, while those of the C fibres were 1.50, 2.44 and 2.07 mmol litre-1. In general, nerves from young and old rabbits were more sensitive to local anaesthetic-induced conduction blockade, suggesting that smaller doses of local anaesthetic are required clinically for anaesthesia in paediatric and older age groups.

Action Potentials↗
PubMed1987

Pharmacokinetics and pharmacodynamics of vecuronium administered by bolus and infusion during halothane or balanced anesthesia.

Vecuronium was administered to two patient groups as a single intravenous dose, 60 micrograms/kg, combined with an infusion, 1 microgram/min/kg. Anesthesia was maintained for the first group with a halothane-nitrous oxide technique; the second group received fentanyl-barbiturate-tranquilizer-nitrous oxide. As the infusion ended, plasma vecuronium concentrations were 0.34 (+/- 0.10) microgram/ml for the halothane group and 0.32 (+/- 0.07) microgram/ml for the fentanyl group, associated with 93% (+/- 8) and 88% (+/- 10) twitch depression, respectively. Vecuronium plasma concentration-time data were combined with the simultaneous intensities of neuromuscular blockade to model the kinetic-dynamic values for each patient. For the halothane group the steady-state volume was 0.21 (+/- 0.04) L/kg, the clearance was 2.9 (+/- 0.1) ml/min/kg, and the elimination half-life was 100 (+/- 36) minutes; for the fentanyl group these were 0.20 (+/- 0.08) L/kg, 3.2 (+/- 0.1) ml/min/kg, and 84 (+/- 43) minutes, respectively. Plasma concentrations associated with 50% blockade averaged 0.2 microgram/ml for both groups. Neither the pharmacokinetics nor the pharmacodynamics of vecuronium in humans differed between these two patient groups.

Adult↗
PubMed1987

Metocurine kinetics in patients undergoing operations requiring cardiopulmonary bypass.

Metocurine kinetics were determined in 10 patients undergoing operations requiring hypothermic cardiopulmonary bypass (CPB) and nine patients of similar age undergoing operations of similar duration but not requiring CPB. The metocurine dosage regimen was a bolus of 0.3 mg/kg given concomitantly with the commencement of an infusion at a rate of 0.04 mg/kg/hr; this regimen was designed to produce and maintain a plasma metocurine concentration associated with 95% depression of the twitch response. Metocurine kinetics were affected minimally by hypothermic CPB. The kinetic parameters including volumes of distribution at steady state of 0.35 L/kg and 0.34 L/kg and elimination clearances of 1.3 ml/min/kg and 1.1 ml/min/kg in the control and CPB groups, respectively, are in agreement with the results of others. Changes in neuromuscular blockade with the onset of CPB and the return to original blockade intensities with rewarming suggest a decreased sensitivity to the effects of metocurine at lower temperatures.

Cardiopulmonary Bypass↗
PubMed1987

Blockade of contralateral carotid sinus nerve enhances ipsilateral nerve action potentials under halothane anaesthesia.

In 10 dogs, one carotid sinus was isolated from the systemic circulation without disturbing its sympathetic innervation. The isolated sinus was connected to a servo-controlled pressure generator which kept mean intrasinus pressure, pulse pressure, and frequency of pulsation constant. The carotid sinus baroreceptor nerve action potentials (NAP) were measured, together with the intransinus and systemic pressures. Following control measurements, the end-tidal concentrations of halothane in oxygen were varied between 0.0 and 2%, in random increments of 0.5%, each with 30 min of stabilization. The carotid sinus NAP response to halothane was biphasic in a dose-dependent manner. The series was repeated after neural blockade of the contralateral sinus with 1% lignocaine 2-3 ml. This blockade enhanced all NAP responses (P less than 0.001), suggesting that a central inhibitory effect, initiated by the contralateral sinus, had been removed.

Action Potentials↗
PubMed1987

Alcuronium pharmacodynamics in dogs: effect-concentration relationships in the diaphragmatic and limb muscles.

Previous studies suggest that the muscles of the diaphragm are less sensitive to neuromuscular blocking agents than the limb muscles. However, this difference has not been characterized directly in terms of relaxant drug plasma concentrations. The pharmacodynamics of the non-depolarizing muscle relaxant alcuronium were therefore investigated in nine dogs using a constant-rate infusion regimen with simultaneous measurement of muscle paralysis in the limb and diaphragm. Maximum paralysis between 95 and 100% was achieved in both muscle groups, within approximately the same time interval. However, during onset of and offset of effect, the pharmacodynamic parameters ECp50 and ECp95 for the limb muscle were lower than in the diaphragm. From a pharmacodynamic effect model it was also predicted that Css(50) and Css(95) for the limb muscles are half those values for the diaphragm. Thus, the diaphragm is less sensitive to the action of alcuronium than are limb muscles. The half-time for equilibration of alcuronium between plasma and the effect site was two-fold lower for the diaphragm, and the rate of recovery from paralysis in diaphragmatic muscles was twice that observed in limb muscles. Collectively, these data suggest that there is a greater margin of safety in the diaphragmatic muscles and that the response of the peripheral limb muscles to nerve stimulation provides only a conservative index of recovery from competitive neuromuscular block in the diaphragmatic muscles.

Alcuronium↗
PubMed1986

Reappearance of the train-of-four after neuromuscular blockade induced with tubocurarine, vecuronium or atracurium.

The characteristics of train-of-four recovery after atracurium or vecuronium were studied, under enflurane anaesthesia, and compared with those associated with tubocurarine-induced blockade. Ten patients each received vecuronium 0.1 mg kg-1, atracurium 0.5 mg kg-1 or tubocurarine 0.5 mg kg-1. Neuromuscular blockade was calculated as the percent depression of the first twitch, and was determined at the time of reappearance of the second, third and fourth twitches of the train-of-four. The pattern during recovery from blockade induced by the three neuromuscular blocking agents was similar, with T2, T3 and T4 reappearing at approximately 93%, 89% and 86% residual blockade, respectively. These results are different from those previously reported by Lee (1975) indicating that, under enflurane anaesthesia, the train-of-four count may give an incorrect estimate of the degree of neuromuscular blockade.

Adult↗
PubMed1986

Comparison of visual and measured train-of-four recovery after vecuronium-induced neuromuscular blockade using two anaesthetic techniques.

This study evaluated train-of-four recovery after the administration of vecuronium, comparing measured with visually observed responses. Responses to supramaximal stimuli of the ulnar nerves were measured by a force transducer, and compared with visually observed movements of the contralateral thumb. For the 10 patients anaesthetized with nitrous oxide and enflurane, the second, third and fourth twitches visually reappeared at 84 (+/- 10)%, 76 (+/- 11)%, and 70 (+/- 12)% measured blockade, respectively. For the other 10 patients, anaesthetized with a narcotic-barbiturate technique, the second, third and fourth twitches reappeared at 81 (+/- 8)%, 68 (+/- 9)%, and 59 (+/- 11)%. These results were not different for the two anaesthetic techniques.

Anesthesia, General↗