Entropy monitoring

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Entropy monitoring is a relatively new method of assessing anaesthetic depth. It was commercially developed by Datex-Ohmeda, now part of GE Healthcare.

It relies on a method of assessing the degree of irregularity in electroencephalogram (EEG) signals. The founding principle behind this theory is that the irregularity within an EEG signal decreases with increasing brain levels of anaesthetic drugs. If we relate the irregularity to the entropy within the signal, then an entropy scale can be assigned.

The signal is captured via a forehead mounted sensor, in a similar way employed by bispectral index (BIS).

Entropy monitors produce two numbers (RE - Response Entropy, SE- State Entropy) that are related to frequency bandpass used. Response Entropy incorporates higher frequency components that include that of electromyogram activity. The reason for using higher frequency bandpass in response entropy is to allow faster response from the monitor in relation to clinical state.

Published studies show that entropy scores do relate to clinical levels of anaesthetic depth. Most anaesthetic drugs are detectable by entropy monitoring, a notable exception being nitrous oxide, in common with BIS monitoring. Future studies may show reduced levels of intraoperative awareness when using this type of monitoring. Future studies may also look into possibilities of influence on outcome when using depth of anaesthesia monitoring.

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 roughly correlated to the likelihood of awareness.

References

Bein B: Entropy:Best practice&research clinical anesthesiology.Vol 20. No 1.,pp. 101-109, 2006

v t e Anesthesia (outline)

Types	General Spinal Epidural Regional anaesthesia Local Topical Intercostal nerve block Sedation / Twilight anesthesia Dental (Inferior alveolar nerve) Neuroleptanalgesic anesthesia

Techniques	Airway management Anesthesia provision in the US Arterial catheter Bronchoscopy Capnography Dogliotti's principle Drug-induced amnesia Intraoperative neurophysiological monitoring Nerve block Penthrox inhaler Tracheal intubation

Scientific Principles	Concentration effect Fink effect Minimum alveolar concentration Second gas effect

Measurements	ASA physical status classification system Baricity Bispectral index Direct Fick method Entropy monitoring Fick principle Goldman index Guedel's classification Mallampati score Neuromuscular monitoring Thyromental distance

Instruments	Anaesthetic machine Anesthesia cart Boyle's machine Gas cylinder Laryngeal mask airway Laryngeal tube Medical monitor Odom's indicator Relative analgesia machine Vaporiser

Drugs	Benzodiazepine Etomidate General anaesthetic Inhalational anaesthetic Infiltration analgesia Ketamine Local anesthetic Methohexital Methoxyflurane Midazolam Neuraxial blockade Opiate Propofol Thiopental Thiopentone

Complications	Emergence delirium Allergic reactions Anesthesia awareness Local anesthetic toxicity Malignant hyperthermia Perioperative mortality Postanesthetic shivering Postoperative nausea and vomiting Postoperative residual curarization

Fields of study	Cardiothoracic Geriatric Oral sedation dentistry

Professions	Anesthesiologist Anesthesiologist assistant Nurse anesthetist Operating Department Practitioners Certified Anesthesia Technician Certified Anesthesia Technologist Anaesthetic technician

History	A.C.E. mixture Helsinki Declaration for Patient Safety in Anaesthesiology History of general anesthesia History of neuraxial anesthesia History of tracheal intubation

Organizations	American Association of Nurse Anesthetists American Society of Anesthesia Technologists & Technicians American Society of Anesthesiologists Anaesthesia Trauma and Critical Care Association of Anaesthetists of Great Britain and Ireland Association of Veterinary Anaesthetists Australian and New Zealand College of Anaesthetists Australian Society of Anaesthetists International Anesthesia Research Society

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Entropy monitoring

See also

References