British journal of anaesthesia
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Randomized Controlled Trial Clinical Trial
Low-dose mivacurium supplementation of prilocaine i.v. regional anaesthesia.
We have compared in two groups of five healthy volunteers, the motor effect of prilocaine i.v. regional anaesthesia of the forearm with and without addition of mivacurium 0.6 mg. Although addition of mivacurium might, theoretically, provide the benefit of increased neuromuscular block with rapid plasma cholinesterase degradation in the isolated limb, we observed prolonged forearm weakness in the mivacurium group using tests of grip strength (median recovery to 90% of control, 80 min (range 60 min to > 8 h) vs control median recovery to 90% of 16 (8-24) min) and bead transfer (median recovery to 90% of control 36 (24-48) min vs control median recovery to 90% of 12 (8-16) min). This weakness was considerably in excess of that predicted by rapid systemic degradation of mivacurium. The mivacurium group experienced symptoms of local anaesthetic toxicity which did not occur in the control group and which could not be replicated by administration of mivacurium alone.
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We studied four electrophysiological variables (bispectral index (BIS), 95% spectral edge frequency (SEF), median frequency (MF) and auditory evoked potential index (AEP index) in 10 patients during emergence from anaesthesia. We compared correlation of the signals with gradually decreasing calculated blood propofol concentrations, and evaluated the signal differences between preinduction and emergence from anaesthesia. Values of BIS, MF and SEF correlated with calculated blood concentrations of propofol during emergence from anaesthesia. ⋯ Although AEP index values did not correlate with calculated blood concentrations of propofol during emergence from anaesthesia, values after eye opening and before anaesthesia were well distinguished from those during emergence from anaesthesia. BIS correlated best with calculated blood concentrations of propofol. AEP index appeared to distinguish the awake from asleep state.
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The maximum recommended dose for extradural infusions of bupivacaine in children older than 1 month is 0.5 mg kg-1 h-1 but there are few specific reports of the associated blood concentrations during infusions in babies. Toxic symptoms can occur in children at plasma concentrations of bupivacaine as low as 2 micrograms ml-1. We attempted to measure venous plasma concentrations of total and free bupivacaine in babies aged 3-12 months during extradural infusions given at a rate commonly used in our hospital. ⋯ One baby had a concentration of 2.02 micrograms ml-1 at 32 h and showed clear evidence of accumulation of bupivacaine. Babies can accumulate bupivacaine and achieve plasma concentrations above the threshold for toxic side effects, despite infusion rates below the currently accepted maximum. The samples size in our study was small but we believe an extradural infusion rate of 0.375 mg kg-1 h-1 is probably an absolute maximum for babies younger than 12 months.
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We undertook a study to observe if a preformed curved plastic cannula, the Trachojet, could be passed blindly down a laryngeal mask airway into the trachea in 100 anaesthetized patients. Using air aspiration and a fibreoptic scope to confirm placement of the cannula, it passed into the trachea in only 27% of patients. The air aspiration technique used for detecting tracheal cannulation was 100% successful when the cannula was inserted fully. We conclude that it may not be possible to gain access to the trachea with a Trachojet for drug administration if a laryngeal mask airway is used to maintain the patient's airway.