British journal of anaesthesia
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I report two patients undergoing open heart surgery, with nitrous oxide and isoflurane anaesthesia, for whom bispectral index (BIS) monitoring showed high BIS values with nitrous oxide and isoflurane anaesthesia. The BIS decreased immediately after nitrous oxide was stopped and increased again after nitrous oxide was restarted.
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Randomized Controlled Trial Clinical Trial
Sedative, analgesic and cognitive effects of clonidine infusions in humans.
This placebo-controlled, randomized study evaluated, on separate days, the dose-response relationship for 1 h infusions of clonidine 1, 2 and 4 microg kg(-1) h(-1), in eight healthy volunteers aged 22-30 yr. Response end-points included sedation (bispectral index, visual analogue scale and observer assessment of sedation), analgesia to a cold pressor test, memory (recall of word lists), cognitive function (digit symbol substitution test (DSST)), respiratory function (respiratory rate, end-tidal carbon dioxide, oxygen saturation) and haemodynamic stability (heart rate and mean arterial pressure). ⋯ Statistically significant analgesia, memory impairment and reduced performance on the DSST occurred during 4 microg kg(-1) h(-1) infusions (resulting in a plasma concentration of 2 ng ml(-1). There were no statistically significant changes in cardiorespiratory variables throughout the study.
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Recent research has shown that high-frequency, gamma-band electroencephalographic (EEG) oscillations (40-60 Hz) may be an important marker of the conscious state. We compared the ability of the bispectral index (BIS) to distinguish the awake and anaesthetized states during the induction of general anaesthesia with: (i) components of the BIS (BetaRatio, SynchFastSlow); (ii) a new EEG variable--the median frequency of the first time derivative of the EEG signal (SE50d); and (iii) the SE50d derived from an EEG signal that has had the frequencies above 30 Hz removed (SE50d(30Hz)). Two groups of subjects were studied: (i) nine volunteers undergoing a short propofol infusion until loss of response to verbal command, and (ii) 84 patients undergoing routine anaesthesia for a variety of surgical procedures. ⋯ In the patient group, the BIS components were equivalent to the BIS in separating the awake from the surgically anaesthetized states (area under receiver operating curve: BIS 0.95, SE50d 0.95, BetaRatio 0.96). Using the submental electromyogram (EMG) signal to estimate the frontalis EMG (30-47 Hz) signal, the changes in EMG signal were, on average, about one-tenth the magnitude of the EEG. We conclude that: (i) there exist simpler derived EEG variables that are similar in accuracy to the BIS; (ii) it is important to avoid filtering out the EEG frequencies above 30 Hz; and (iii) in most patients the confounding effects of the frontalis EMG on the EEG are minimal.
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Case Reports
Successful epidural anaesthesia for Caesarean section in a patient with spondyloepiphyseal dysplasia.
Spondyloepiphyseal dysplasia congenita is a rare genetic entity in which it is very important to involve anaesthetists early on to discuss the possible anaesthetic complications for both general or regional anaesthesia. A case is described of a patient with spondyloepiphyseal dysplasia and multifetal pregnancy in which successful epidural anaesthesia for caesarean section was performed.