Benefit of General Anesthesia Monitored by Bispectral Index

Introduction

The unintended awareness in between a surgical procedure despite being under general anesthesia is called anesthesia awareness. It is also called unintended intraoperative awareness. Awareness while under anesthesia is a rare condition. However, it is seen in about one percent of people who are at high risk. It can lead to anxiety and post-traumatic stress disorder. The Joint Commission on Accreditation of Healthcare Organizations (JCAHO) has recommended to take stringent efforts to prevent awareness while under anesthesia. The American Society of Anesthesiologists (ASA) has also published guidelines in this aspect.

What Are the Levels of Anesthesia Awareness?

Jones has described three levels of anesthesia awareness. They include conscious awareness with pain, conscious awareness without pain, and perception without conscious awareness. The spontaneous recollection of incidents with or without pain is termed explicit recall. On the other hand, implicit recall is the changes in behavior caused by previous experiences without conscious recall of the events.

What Is the Psychological Sequelae of Intraoperative Awareness?

Awakening from sedation can be a frightening experience. Some people have experienced signs of paralysis, pain, anxiety, helplessness, and powerlessness while awakening from anesthesia. The placement of an endotracheal tube in the trachea can cause an inability to communicate their distress to the healthcare professional. This can create a sense of fear and anxiety within them.

What Are the Implications of Anesthesia Awareness?

There can not be a standard measurement for the amount of anesthesia to be given to a patient. This is because the requirement for anesthesia might differ from person to person, and there may be uncertain predictions. There are one to two cases in 1000 general anesthesia administration where intraoperative awareness can occur. Studies show that about 43 percent of these people develop post-traumatic stress disorder. The main factor that causes intra-operative awareness is found to be the inadequate dosing of anesthesia given. It could happen when:

• The dosing of the general anesthesia by the healthcare provider was not proper.

• The patient required a higher dose of anesthesia than the given dose.

• The patient could not tolerate the required dose of general anesthesia.

• Malfunctions in the anesthesia delivery system.

• Difficult intubation.

• Premature removal of the anesthesia.

• Errors in intravenous infusion.

• Chronic alcoholopioidpiod use.

What Is Bispectral Index?

The Bispectral index is a multiprocessor parameter of EEG (electroencephalogram) that was specifically designed to assess how anesthetics affect the hypnotic or unconscious state of the brain. It helps in the measurement of the depth of anesthesia. Introducing this index in clinical practice helps in assessing brain function during a surgical procedure. It assesses only the hypnotic component of the anesthesia.

How Is Bispectral Index Monitoring Done?

The BIS technology consists of a sensor, a digital signal converter, and a monitor. The sensor is placed on the patient’s forehead. It collects signals from the cerebral cortex and transfers them to the digital signal converter.

Various descriptors are converted into a single variable by the BIS monitor. Quantifies the changes in the brain while under anesthesia. The BIS score in an awake patient is between 90 to 100. BIS scores fall while a person is asleep, although not as low as when a person is under anesthesia. As the value decreases, the hypnotic effect increases. In general, a BIS below 60 is linked to a lower probability of responding to commands.

What Are the Benefits of the Bispectral Index Monitoring?

There are many methods to measure the depth of anesthesia. Each procedure may have its advantages and disadvantages. Hence, jurisdiction selection of the methods is required in clinical practise. The depth of anesthesia should be measured in any surgical procedure. It helps to prevent any further complications during the procedure. There can be hemodynamic changes (alternations in the blood flow) if too much or a higher than-required dose of anesthesia is given. On the other hand, anesthesia that is too little can cause awareness in the patient during the procedure.

Current literature supports the fact that awareness of BIS has potential benefits, like early recovery from anesthesia, reduced consumption of anestheticheic drug, decreased chance of post-anesthetic cognitive dysfunction (issues related to thinking and reasoning properly), and perioperative risk stratification, a concept allowing ting a numerical value to assess the risk of a patient, which ranges from one (very low risk) to five (very high risk). In addition, it reduces the time for intubation, and reduced chance of delirium (confusion) in the postoperative period.

What Are the Limitations of the Bispectral Index Monitoring?

Some of the limitations of BIS monitoring include:

• It could not specifically measure the sense of being asleep. It lacked the sensitivity to measure the state of awake or sleep accurately. This can result in the administration of a higher dose of anesthesia than is required.

• The sensitivity of the system was 61 percent and had a specificity of 89 percent.

What Are the Factors Affecting Bispectral Index Scores?

• Age: Studies show that BIS monitoring was inefficient in titrating the anesthetic in babies less than six months. The BIS score remained below the required value of 40 despite alterations in the anesthetic dosage. Another study showed that older patients showed higher levels of response at higher BIS scores.

• Anesthetic Agent: Studies show that the BIS score changes with the type of anesthetic agent used.

• Hypothermia: Hypothermia (reduced body temperature) alters the physiologic functions like protein binding, liver and kidney perfusion, and metabolic rate. Studies showed a paradoxical increase in BIS values with cooling and a decrease in values on reheating.

• Interference with Other Medical Devices: BIS scores were often susceptible to interference with other medical devices. BIS values change with the signals from electrical equipment, electrocautery, roller pumps, and anesthesia equipment.

What Are the Other Technologies that Help Quantify the Depth of Anesthesia?

Other alternative technologies that help to quantify the depth of anesthesia include:

• SNAP EEG monitor system.

• Auditory Evoked Potential (AEP) monitor.

• Patient State Analyzer 4000 (PSA 4000).

• Narcotrend.

• Spectral Edge Frequency 95 (SEF 95).

• Automated Responsiveness Test (ART).

Conclusion

BIS monitoring helps to measure the levels of alertness in an individual while under anesthesia. It is commonly used in operating rooms, ICUs, and some emergency departments. It is one of the most widely studied monitors for level of consciousness. However, it does not accurately measure all the changes in the central nervous system while a person is under anesthesia. To date, there is no accurate device to measure the level of consciousness while under anesthesia.