British journal of anaesthesia
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In clinical practice, analgesic drug doses applied during general anaesthesia are considered sufficient when clinical responses (e.g. movement, blood pressure and heart rate elevations) are suppressed during noxious stimulation. We investigated whether absent clinical responses are indicative of suppressed spinal and brain responsiveness to noxious stimulation in anaesthetised subjects. ⋯ Nociceptive activation persists during deep general anaesthesia despite abolished clinical responses. Absent clinical responses are therefore not indicative of absent nociception-specific activation. Thus, commonly accepted clinical responses might be inadequate surrogate markers to assess anti-nociception during general anaesthesia. Further research is required to investigate whether persistent nociception causes adverse effects on patient outcome.
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Transitions into and out of the anaesthetised state exhibit resistance to state transitions known as neural inertia. As a consequence, emergence from anaesthesia occurs at a consistently lower anaesthetic concentration than induction. Motivated by stochastic switching between discrete activity patterns observed at constant anaesthetic concentration, we investigated the consequences of such switching for neural inertia. ⋯ Stochastic state switching accounts for all known features of neural inertia. More than two states are required to explain the consistent increase observed in variability of recovery from general anaesthesia. This model predicts that hysteresis should collapse with a time scale independent of anaesthetic drug pharmacokinetics.