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Near-Infrared Spectroscopy For The Evaluation Of Anesthetic Depth
Huyền Diệu - 22/06/2024
INTRODUCTION
Figure 1: Anesthetic depth monitoring.
Anesthetic depth refers to the level of unconsciousness and pain suppression achieved during surgery or other procedures requiring anesthesia. It's not a simple on/off switch, but rather a spectrum with different levels offering varying degrees of unconsciousness and pain control.
Here's level of anesthetic depth:
No Anesthesia: The patient is fully awake and feels pain.
Light Anesthesia: The patient may be drowsy or confused but can still respond to stimuli like commands or pain.
Moderate Anesthesia: The patient is unconscious and doesn't respond to verbal commands but may react to painful stimuli with reflex movements.
Deep Anesthesia: The patient is completely unconscious and doesn't respond to any stimuli, including pain. Their breathing and reflexes might be depressed, requiring monitoring and support.
Importance of Maintaining Anesthetic Depth:
An appropriate anesthetic depth is crucial for a safe and successful procedure. It ensures the patient remains unconscious and pain-free throughout the surgery. However, excessively deep anesthesia can lead to complications like respiratory depression and delayed recovery.
Anesthesiologists carefully manage anesthetic depth using various medications and monitoring techniques throughout the procedure.
METHOD
Near-Infrared Spectroscopy: A Potential Game Changer in Anesthesia Monitoring
During surgery, maintaining the ideal anesthetic depth is crucial for patient safety and comfort. Traditionally, this has relied on monitoring vital signs like heart rate and blood pressure, or observing responses to stimuli. However, these methods are subjective and don't directly reflect brain activity. Modern tools like BIS(Bisspectral Index) and entropy offer better insights, but they can be expensive and require specialized equipment.
This is where Near-Infrared Spectroscopy (NIRS) emerges as a promising alternative. NIRS is a non-invasive technique that utilizes near-infrared light to measure changes in blood flow and oxygenation within the brain. Here's why it holds exciting possibilities for anesthesia depth evaluation:
Non-invasive and painless: Unlike some techniques, NIRS doesn't require injections or probes, making it a comfortable option for patients.
Potentially cost-effective: The technology is relatively simpler compared to other monitoring methods, potentially leading to lower costs.
Real-time feedback: NIRS provides continuous data, allowing anesthesiologists to monitor brain activity in real-time and adjust anesthetic levels as needed.
Figure 2: Schematic diagram of the fNIRS system.
NIRS for monitoring anesthetic depth does not directly measure the level of anesthesia, but rather focuses on indirect effects caused by the anesthetics on the brain. Here is how it works:
NIRS utilizes near-infrared light (660-940 nm) which can penetrate through scalp and skull.
Brain activity is linked to blood flow and oxygen consumption. When under anesthesia, brain activity decreases, which leads to changes in blood flow and oxygenation.
NIRS measures the absorption of light by different molecules in the brain tissue, including oxyhemoglobin (HbO2) and deoxyhemoglobin (HbR). HbO2 carries oxygen, while HbR is hemoglobin without oxygen.
By analyzing the changes in HbO2 and HbR concentration, NIRS can provide insights into the brain's oxygenation state, which can be indirectly linked to the depth of anesthesia.
Here is a breakdown of the connection between NIRS data and anesthesia depth:
Increased Anesthesia: As anesthesia deepens, brain activity decreases, leading to a decrease in oxygen consumption.
NIRS might show an increase in HbO2 (more oxygen available) and a decrease in HbR (less oxygen being used) compared to the awake state.
Figure 3: fNIRS response before and after induction of propofol.
Figure 3 depicts the changes in brain oxygenation using fNIRS (functional near-infrared spectroscopy) following propofol anesthesia induction in an adult patient. The X-axis represents time, starting from the awake state (baseline) and continuing for a few minutes after propofol injection. The Y-axis shows two lines: HbO2, representing the concentration of oxygen-carrying hemoglobin (oxyhemoglobin) in the brain tissue, and HbTot, representing the total hemoglobin concentration (both HbO2 and HbR, hemoglobin without oxygen). The result suggests that propofol anesthesia typically increases both HbO2 and HbTot compared to the awake state. Therefore, Figure 3 likely shows an increase in the HbO2 line after propofol injection, indicating more available oxygen in the brain. The HbTot line might also increase due to changes in blood flow.
APPLICATION
Near-Infrared Spectroscopy: Transforming Anesthesia Care.
With advancements in technology and data analysis, NIRS has the potential to become a valuable tool in the anesthesiologist's toolkit:
Improved patient care: By providing a more objective and continuous picture of brain activity, NIRS can contribute to more precise control of anesthetic depth, minimizing the risk of complications and optimizing recovery times.
Broader accessibility: The potentially lower cost and simpler technology of NIRS could make advanced anesthesia monitoring more accessible in various clinical settings.
Conclusion
While NIRS isn't currently a standard practice for anesthesia depth evaluation, its potential for non-invasive, real-time monitoring makes it a technology worth watching. As research continues to refine its applications, NIRS has the potential to revolutionize the way we monitor patients under anesthesia, leading to safer and more personalized care.
