Entropy monitoring
Encyclopedia
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 expressing the likelihood of awareness.
GE Healthcare
GE Healthcare is a division of GE Technology Infrastructure, which is itself a division of General Electric . It employs more than 46,000 people worldwide and is headquartered in Little Chalfont, Buckinghamshire, United Kingdom. GE Healthcare is the first GE business segment to be headquartered...
.
It relies on a method of assessing the degree of irregularity in electroencephalogram (EEG
EEG
EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...
) 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
Information entropy
In information theory, entropy is a measure of the uncertainty associated with a random variable. In this context, the term usually refers to the Shannon entropy, which quantifies the expected value of the information contained in a message, usually in units such as bits...
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
Bispectral index
Bispectral index is one of several technologies which purport to monitor depth of anesthesia. BIS monitors are intended to replace or supplement Guedel's classification system for determining depth of anesthesia...
(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
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
, 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
Vital signs
Vital signs are measures of various physiological statistics, often taken by health professionals, in order to assess the most basic body functions. Vital signs are an essential part of a case presentation. The act of taking vital signs normally entails recording body temperature, pulse rate ,...
such as pulse
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...
, heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
, blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
, and movement are indirect indicators of consciousness, and when these are combined with expired gas analysis of inhalational anaesthetic
Inhalational anaesthetic
An inhalational anaesthetic is a chemical compound possessing general anaesthetic properties that can be delivered via inhalation. They are administered by anaesthetists through an anaesthesia mask, laryngeal mask airway or tracheal tube connected to some type of anaesthetic vaporiser and an...
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
Bispectral index
Bispectral index is one of several technologies which purport to monitor depth of anesthesia. BIS monitors are intended to replace or supplement Guedel's classification system for determining depth of anesthesia...
) or Entropy, are converted to a number expressing the likelihood of awareness.