Overview of Bispectral Index
During any medical procedure, it is crucial to monitor how deeply a patient is anesthetized. If a person is under too deep of an anesthesia, it can lead to changes in the body’s internal equilibrium, such as blood pressure and heart rate. On the other hand, if the anesthesia is too light, the patient may remember parts of the procedure or be aware during the procedure.
Being aware during a time when you’re supposed to be unconscious due to anesthesia is a very serious complication. It can lead to long-term mental health issues like anxiety and post-traumatic stress disorder. This is why it’s extremely important to make sure the patient is neither too deeply nor too lightly anesthetized.
The bispectral index, or BIS, is a scale that doctors use to measure the depth of anesthesia. The goal is to keep the BIS value below 60, which helps to lower the chances of a patient being aware during the procedure. Several tools that monitor nervous system activity have been created to measure anesthesia depth. The BIS monitor is the first method approved by the FDA to measure the effects of drugs used to induce a state of unconsciousness.
Anatomy and Physiology of Bispectral Index
The Bispectral Index (BIS) is a significant tool that helps doctors understand how deeply a patient is under anesthesia. It provides feedback in real-time and helps doctors ensure that patients are neither too deeply anesthetized nor too aware during the process.
The BIS works by translating brain activity into a simple number from 0 to 100. A score of 0 means the brain is entirely inactive, and 100 means the patient is fully awake and alert. This number comes from an analysis of a patient’s brainwaves, also known as an electroencephalogram (EEG). This analysis looks at things like frequency, phase, and power spectrum. So, by using the BIS, doctors can objectively understand how conscious or unconscious the patient is, allowing them to adjust the anesthesia accordingly.
However, the BIS isn’t perfect. Because it relies on complex calculations, there can be time delays between changes in the anesthesia and what the BIS shows. This delay can make it harder for doctors to interpret the BIS values. Some research has shown this delay can be up to 104 seconds, which could have an impact on how doctors manage the anesthesia. These potential implications mean that further studies are needed.
The BIS system is also used in anesthesiology to see how deep the anesthesia is. It does this by looking at the concentration of power in specific frequency ranges. Anesthetics can affect gamma waves, and gamma waves are linked with things like memory, cognitive function, and information processing. As a result, these waves are part of the BIS score. Neat, isn’t it? But neuromuscular blockades can also affect the BIS score, even in people who are awake. Additionally, the system uses the concentration of power and another measure called Wiener entropy to estimate how much information is in the EEG and how it is distributed over the frequency spectrum.
Why do People Need Bispectral Index
The Bispectral Index (BIS) is a valuable tool used by doctors during anesthesia administration. It measures how deep someone is under anesthesia. This use of this technology is significant for a few reasons.
First, it can help prevent “intraoperative awareness,” a distressing experience where a patient becomes conscious while under anesthesia. Research suggests that using BIS to guide how much anesthesia is provided can lessen the chances of this event happening.
The tool is also useful for patients who are at high risk for postoperative cognitive dysfunction (POCD) and postoperative delirium (POD). POCD refers to problems with thinking, memory, and concentration after surgery. POD is sudden confusion after surgery. Studies indicate that using BIS to determine the depth of anesthesia could potentially lower the chances of POD and POCD occurring, especially in high-risk patients. BIS helps to ensure a balanced amount of anesthesia is given, which can help prevent unnecessary cognitive problems after surgery.
Another advantage of using BIS is that it may aid in early recovery after an operation. Research shows it can guide anesthesia depth, resulting in quicker wake-up times from anesthesia and shorter stays in the recovery room. Less duration in the recovery room means better efficiency in healthcare resources utilization.
Though BIS is an exceptional tool, it’s not without its challenges. One issue is the delay in BIS response to changes in anesthesia, which needs to be factored in to ensure the best care. Study on this tool to improve its potential and benefits for patients is still ongoing.
Recent studies reveal that if anesthesia is given based on BIS monitoring, patients feel less pain during the first hour right after surgery, but it can also lead to an increased chance of delirium. Other research suggest aiming for a higher BIS to reduce POD and POCD three months after surgery, but there’s no evidence that it affects the duration of the hospital stay or the rate of death in patients.
Equipment used for Bispectral Index
The BIS monitor is a tool used by doctors to understand how conscious a patient is. It works by analyzing brain signals, or EEG signals, that are picked up through sensors. Once collected, these signals are interpreted by a special program within the device. This interpretation is then shown as a number on the monitor, ranging from 0 to 100.
A BIS monitor reading of 0 means there is no brain activity, while a reading of 100 means the patient is fully awake. If the monitor displays a number less than 40, this indicates that the patient is in a deep state of relaxation or hypnosis. However, when the BIS monitor reads a number between 40 and 60, it shows that the patient is under the right level of general anesthesia for surgery and won’t be aware of what is happening.
How is Bispectral Index performed
BIS monitoring, a method of observing brain activity during anesthesia, requires applying four sticky patches called electrodes on the forehead. First, the forehead is cleaned with an alcohol wipe, then slight pressure is applied over the patches for 2 to 5 seconds to ensure they stick properly.
The patches include wet gel electrodes that are thrown away after each use. One of these electrodes, electrode 4, measures the muscle movement of the forehead and serves as the grounding electrode. There are two types of monitors available, one displays information on two-channels and the other uses four-channels with greater capability. Extended sensors are also available for patients in the ICU who need longer periods of monitoring. For children, a special pediatric sensor is available that can capture weaker brain signals (EEG).
The information displayed on the BIS monitor includes:
- The BIS number, a compact score of brain activity,
- A trend graph showing changes in the BIS values over time,
- Raw EEG patterns visible in real-time,
- Several indicators of signal quality such as the SQI (signal-quality-index) and EMG (a measure of muscle movement),
- Alerts and messages.
The SQI bar visually indicates the reliability of the signal; a higher SQI means the BIS number is more reliable. The EMG bar shows muscle activity, which indicates whether the muscle is experiencing increased tone or movement.
The BIS monitoring system works by using a special sensor attached to the patient’s forehead and temple. This sensor records the brain’s electrical activity, or EEG, which is then analyzed by a special algorithm to calculate a BIS value. This value is displayed on a monitor, giving real-time information about the level of anesthesia.
Although the BIS system is designed to be easy to use, there are certain factors that may affect its accuracy. For instance, if the EMG registers an increase in muscle movement, the BIS values may also increase, which could lead to misunderstanding the patient’s level of consciousness. Therefore, it’s important to apply and secure the BIS sensor properly to get accurate readings. Additionally, certain medications like ketamine and nitrous oxide can cause the BIS values to increase despite causing deep levels of sedation. Thus, BIS values should be interpreted along with other clinical information and not be the only guide to the depth of anesthesia.
Possible Complications of Bispectral Index
There are several factors that can limit the effectiveness of BIS (Bispectral Index) Monitoring, a tool that helps doctors monitor how deep a patient is under anesthesia during surgery.
* Anesthetic drugs: The type of anesthetic drugs used can affect BIS readings. In other words, a patient given a specific drug could appear to be more sedated than another patient who had a different combination of drugs, despite having the same BIS score. Certain anesthetics, like ketamine and nitrous oxide, can cause the BIS monitor to be unreliable. In fact, nitrous oxide has been found to increase BIS values because it reduces the strong effect that inhaled anesthetics have on electrical brain activity (EEG) and it also stimulates the brain’s activity.
* Age: Using BIS to figure out the correct dose of anesthetics for infants younger than 6 months can be tricky. This is likely because infants’ brains are still developing, so their EEG readings may differ from older children. A study found that there was no significant difference in anesthetic use or recovery measures between standard practice and using BIS in children aged 6 months to 3 years.
* Hypothermia: Cold body temperatures can also cause BIS readings to become unreliable. When body temperature drops, BIS values tend to decrease. The lowering in temperature leads to less oxygen being used by the brain, which can cause the EEG readings to change. Aortic cannulation, which is the insertion of a tube into the aorta, can also cause EEG slowing, as can starting certain types of heart-lung machine procedures.
* Neurological impairment: For patients with brain injuries or diseases, the BIS method is not reliable in assessing their level of consciousness. These patients usually have lower BIS values. BIS measures brain activity in the outer layer of the brain, it doesn’t measure deeper structures, like the spinal cord.
* Interference with medical devices: Medical devices can interfere with BIS monitoring and cause inaccurate readings. For instance, the use of electrically heated surgical tools has been found to decrease the quality of BIS readings.
What Else Should I Know About Bispectral Index?
There are several types of technologies doctors use to monitor how deeply an individual is under anesthesia (a state of temporary induced loss of sensation or awareness). Some of these include the SNAP EEG monitor system, the auditory evoked potential monitor, 4-channel processed EEG, EEG monitor, Spectral edge frequency 95, and the Automated responsiveness test.
One popular choice is the BiSpectral Index (BIS), which uses brain wave patterns to measure how deeply a patient is anesthetized. However, there are other options as well. Each option has its own benefits and drawbacks and are used depending on the person’s specific medical needs.
For example, Spectral Entropy monitoring is another method. Like the BIS, it also uses brain activity (EEG data), but provides two measurements: response entropy (RE) and state entropy (SE). RE includes muscle activity (EMG data) and brain activity, while SE only represents brain activity. This technology might offer a more detailed understanding of the patient’s consciousness.
The Narcotrend index is another alternative to BIS. This monitor also uses EEG data but uses a different calculation method. It classifies how deeply a person is under anesthesia into 6 stages, ranging from being awake (A) to fully anesthetized with complete cessation of brain activity (F). This method has shown potential in guiding anesthesia delivery and predicting if a patient is going to wake up during surgery. However, more research is needed to fully understand its benefits.
The patient state index (PSI) is another method that assesses anesthesia depth using EEG data. PSI operates on a scale of 0 to 100, with lower numbers meaning the patient is more deeply anesthetized. Research has shown that PSI may accurately determine the anesthesia depth and stays relatively stable despite surgical stimulation.
Lastly, the A-line autoregressive index (AAI) utilizes a different method by using auditory evoked potentials (AEP) to measure how deeply a patient is anesthetized. AEPs are signals produced by the brain in response to sound. It’s been suggested that AAI can be useful in administering anesthesia, offering an alternative to the EEG-based approaches.
In conclusion, while BIS is a commonly used method to assess the depth of anesthesia, there are many alternatives. These alternatives have their unique strengths and weaknesses. The choice will depend on the individual patient’s situation. Continued research and education in this area are needed to best serve patients.