British journal of anaesthesia
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The isolated forearm technique (IFT) enables an otherwise paralysed patient to communicate awareness to the anaesthetist. We present a debate that focuses on how best to interpret IFT responses. On one side, Pandit argues that there is a range of response types from none through to movement initiated by the patient to alert the researcher. ⋯ In rebuttal, Russell and Wang argue that IFT response types are not so discrete, and that the IFT technique precludes higher levels of response. They argue that overinterpretation of IFT responses might in fact result in a greater risk of accidental awareness; a binary interpretation of the IFT response is the safest option. All authors agree that the IFT has a role in clinical practice and the study of anaesthetic mechanisms.
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The use of EEG monitors to assess the level of hypnosis during anaesthesia has become widespread. Anaesthetists, however, do not usually observe the raw EEG data: they generally pay attention only to the Bispectral Index (BIS™) and other indices calculated by EEG monitors. This abstracted information only partially characterizes EEG features. ⋯ EEG waveforms vary in the presence of noxious stimuli (surgical skin incision), which is not always reflected in BIS™, or other processed EEG indices. Spindle waves are adequately sensitive, however, to noxious stimuli: under surgical anaesthesia they disappear when noxious stimuli are applied, and reappear when adequate analgesia is obtained. To prevent awareness during anaesthesia, I speculate that the most effective strategy is to administer anaesthetic agents in such a way as to maintain anaesthesia at a level where spindle waves predominate.
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The mechanisms by which volatile anaesthetics such as isoflurane alter neuronal function are poorly understood, in particular their presynaptic mechanisms. Presynaptic voltage-gated sodium channels (Na(v)) have been implicated as a target for anaesthetic inhibition of neurotransmitter release. We hypothesize that state-dependent interactions of isoflurane with Na(v) lead to increased inhibition of Na(+) current (I(Na)) during periods of high-frequency neuronal activity. ⋯ Isoflurane stabilises the fast-inactivated state of neuronal Na(v) leading to greater depression of I(Na) during high-frequency stimulation, consistent with enhanced inhibition of fast firing neurones.
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Clinical Trial
Prediction of fluid responsiveness using a non-invasive cardiac output monitor in children undergoing cardiac surgery.
This study evaluated the ability of a non-invasive cardiac output monitoring device (NICOM) to predict fluid responsiveness in paediatric patients undergoing cardiac surgery. ⋯ ClinicalTrials.gov NCT01996956.
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General anaesthesia induces highly structured oscillations in the electroencephalogram (EEG) in adults, but the anaesthesia-induced EEG in paediatric patients is less understood. Neural circuits undergo structural and functional transformations during development that might be reflected in anaesthesia-induced EEG oscillations. We therefore investigated age-related changes in the EEG during sevoflurane general anaesthesia in paediatric patients. ⋯ Sevoflurane-induced EEG dynamics in children vary significantly as a function of age. These age-related dynamics likely reflect ongoing development within brain circuits that are modulated by sevoflurane. These readily observed paediatric-specific EEG signatures could be used to improve brain state monitoring in children receiving general anaesthesia.