The basic principle and use of anesthesia machine depth monitor
With the development of medical sensor technology and electronic technology, patient monitoring technology has developed rapidly, and the monitoring of various physiological parameters has been increasing. The depth of anesthesia monitoring is a monitor developed in recent years to quantify the hypnotic state of patients during anesthesia. To monitor the hypnotic state of the patient’s brain when using anesthetics and other drugs to better protect the patient’s life safety.
The current depth of anesthesia monitoring uses two technologies, auditory evoked potentials and brain waves EEG monitoring technology or a combination of the two. Patients must be given sufficient anesthesia during surgery and intensive care treatment to relieve the pressure of the patient. For light sleep state, indirect measurement (including auditory evoked potential test) is carried out by observing clinical signs and the patient's response to sound and sensation. These evaluation standards are applicable in some cases, but there are certain limitations. The above method is not suitable for patients who cannot respond. For those patients who can respond, the stimulation caused by the measurement may also awaken the patient. And because the auditory evoked potential test involves too many transmission pathways and nerves, it is difficult to be accurate and anti-interference.
The EEG will change from a low-amplitude high-frequency signal to a high-amplitude low-frequency signal as the state of awake to deep anesthesia changes. Sedative drugs can increase mid/high frequency activity or "l3 activation". When the drug is increased and consciousness is gradually lost, the low-frequency vibration will increase, and the overall EEG amplitude will increase significantly compared to when awake. In the deeper hypnotic state, not only the consciousness is lost, but the higher frequencies also disappear completely, and the entire amplitude is much larger than when waking. At higher doses of the drug, all activities disappear and a zero potential EEG is formed.
Aspect Medical Systems improved the calculation of EEG parameters and obtained the Bispectral Index (BIS) to evaluate the effects of anesthetics on the patient’s brain. The BIS index reflects the effect of anesthetics and sedatives on the depth of anesthesia consciousness.
EEG can be split into a series of sine waves. BIS analysis can study the correlation and coupling between sine waves. In particular, BIS analysis quantifies the synchronization level of EEG through traditional amplitude and frequency parameters. Aspect Company simplified the complex data group in the BIS analysis into a composite number-BIs index through complex calculation rules, thereby describing changes in the state of the brain. The BIS index is calculated in real time by combining three analysis steps. The first step is the EEG preprocessing program, which decomposes the EEG signal to every second and marks certain parts; the second step is the calculation of the hypnosis/sedation state index, which combines the selected EEG characteristics and uses the above Improved calculation rules; in the third step, use the large-scale database stored in the machine to correct the hypnotic/sedation state index to better reflect the degree of EEG inhibition.
These studies have proved that the BIS value can evaluate the effect of anesthetics on the brain, and the concentration of the drug is related to memory. If the BIS value is lower than 70, there is little memory, and if the BIS value is lower than 60, there is no consciousness. The BIS value of general anesthesia is recommended to be controlled between 40 and 60. BIS can also be used to feed back and display the state of consciousness during conventional anesthesia.
Clinical significance of BIS:
(1) Measure the patient's level of consciousness, directly grasp the depth of the patient's anesthesia, guide the anesthesiologist to give the patient the most appropriate dose of anesthetic drugs, and ensure the safety and benefits of the operation, anesthesia, the patient and the hospital.
(2) Follow-up and monitor the patient's awakening during the operation, and determine whether the degree of anesthesia is insufficient due to the problem of administration, or the drug demand is insufficient due to the stimulation of the patient or the change in the metabolic level.
(3) It can continuously display the recovery of the patient's consciousness after surgery. The patient can detect mild hypnosis by the trend of BIS at least 15 minutes earlier than using 95% sEF.
(4) Help the doctor to wake up the patient faster and predict the patient's wake up.
(5) Evaluate the dynamic effects of drugs acting on the brain.
(6) Estimate the anesthetic components of hypnotics and their effects on the brain.
(7) For complex operations and deep anesthesia, the BIS~ index has a wider monitoring range than the AEP index (AAI).
With the help of BIS~, anesthesia dose can be reduced by 20%-40%, awakening can be accelerated by 35%-40%, and the incidence of nausea and vomiting can be reduced, so that doctors can deal with patients more easily and objectively, and ensure that the most difficult medical records receive the most basic care , Is the trend of anesthesia care in the future.
