British journal of anaesthesia
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Comparative Study Clinical Trial Controlled Clinical Trial
Comparison of the neuromuscular block induced by mivacurium, suxamethonium or atracurium during nitrous oxide-fentanyl anaesthesia.
We compared the neuromuscular and cardiovascular changes following administration of mivacurium 0.15, 0.20 and 0.25 mg kg-1, suxamethonium 1.0 mg kg-1 or atracurium 0.5 mg kg-1 i.v. in 41 (ASA physical status I or II) patients during nitrous oxide-fentanyl anaesthesia. Mean onset times for total ablation of twitch response for mivacurium 0.15, 0.20 and 0.25 mg kg-1, were 2.5, 2.4 and 2.7 min, respectively, similar to that for atracurium (2.5 min), but longer than for suxamethonium (1.1 min) (P less than 0.05). ⋯ Following neostigmine 0.045 mg kg-1, mean times for twitch tension to recover from 10% to 90% of control were similar for mivacurium (9.7 min) and atracurium (10.5 min). Transient decreases in mean arterial pressure (greater than 20%) were observed in seven of 15 patients who received the two higher doses of mivacurium.
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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). ⋯ 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.
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Six patients were anaesthetized with 70% nitrous oxide in oxygen supplemented by infusion of propofol 40, 80, 120, 160 and 200 micrograms kg-1 min-1 sequentially in successive 10-min periods. Auditory evoked response (AER) and lower oesophageal contractility (LOC) were monitored. The AER findings were consistent with those noted in previous studies of i.v. agents. ⋯ Brainstem waves were not affected significantly. LOC, provoked and spontaneous, showed no consistent relationship with blood concentration of propofol. The two variables AER and LOC were not related.
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In a laboratory model, humidity output was investigated in relation to the design of a circle absorber system. A 70-kg subject was simulated with fresh gas flows of 0.5, 2 or 5 litre min-1. Different circle systems, absorption canisters and tubings were studied. ⋯ Coaxial tubing only moderately increased the humidity. If a fresh gas flow of 0.5 liter min-1 was used, optimum moisture contents were attained, irrespective of the circle system tested. Low fresh gas flows, a small canister and an Eger A type circle system, were factors which increased humidification.
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Randomized Controlled Trial Clinical Trial
Haemodynamic changes after induction of anaesthesia and tracheal intubation following propofol or thiopentone in patients of ASA grade I and III.
Thirty-six ASA I patients received either propofol 2.25 (0.07) mg kg-1 (mean (SEM] or thiopentone 4.8 (0.18) mg kg-1, for induction of general anaesthesia together with fentanyl and a neuromuscular blocking drug. This technique was repeated in 12 ASA III patients, using propofol 1.8 (0.18) mg kg-1 or thiopentone 4.7 (0.37) mg kg-1. There was a significant decrease in systolic arterial pressure following induction of anaesthesia with both drugs; this was more pronounced after propofol, and in ASA III patients. Plasma noradrenaline concentrations increased after tracheal intubation only in the thiopentone group, but the pressor response to tracheal intubation was not attenuated by the use of propofol.