Entropy (anesthesiology)

In anesthesiology, entropy is a neurophysiologic monitor of the patient's cerebral cortical function, designed to express the likelihood of consciousness, intraoperative awareness, or awareness with recall during a surgical procedure.

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Other Vital signs such as pulse, heart rate, blood pressure, and movement are indirect indicators of consciousness, and when these are combined with expired gas analysis of inhalational anaesthetic agents, an experienced anaesthetist can be confident a patient is unconscious and not aware of their surroundings. However, the direct measurement of brain activity using a basic EEG is purported to measure effects of anaesthetics more comprehensively. This is because as anaesthesia "deepens", there are predictable changes in the EEG including slowing, synchronicity, and burst suppression, that, in the case of BIS (Bispectral index) or Entropy, are converted to a number expressing the likelihood of awareness.