Research progress on the application of near-infrared spectroscopy technology in monitoring cerebral oxygen and hemodynamics in neurosurgical patients

Preface

The brain tissue consumes a huge amount of oxygen. The weight of the adult brain only accounts for 2% of body weight, but in a quiet state, its blood flow accounts for about 15% of cardiac output, and its oxygen consumption accounts for about 20% of systemic oxygen consumption,According to relevant literature reports, the proportion of people who die from brain injury due to ischemia and hypoxia is as high as 90%.In clinical practice, in order to achieve brain protection, there is an urgent need for technologies that can accurately monitor the real-time blood flow and oxygenation status of brain tissue.

Near infrared spectroscopy (NIRS) is a rapidly developing detection technology in recent years. It can measure local tissue oxygen saturation (rSO)₂）To evaluate the oxygenation status of brain tissue. This article focuses on itThe principle of monitoring andReview the research progress in monitoring cerebral oxygen and hemodynamics in neurosurgery.

Basic principles of near-infrared spectroscopy technology application

Near infrared spectroscopy technology is a continuous real-time optical detection method. Near infrared light has a wavelength between 700-1000nm and has good penetration through human tissues such as scalp and skull, but is less scattered.The main absorber of near-infrared light in the skull is oxygenated hemoglobin (HbO)₂）Compared to reduced hemoglobin (Hb), the two have different absorption spectra, so we can distinguish them using optical methods.

When near-infrared light enters human tissue, the two types of hemoglobin in the tissue will absorb it. We measure the intensity of light emitted from the tissue, and based on the modified Beer Lambert law, we can obtain the local tissue oxygen saturation.There are a large number of microvessels in brain tissue, with arterial blood volume accounting for about 20%, capillary blood volume accounting for about 5%, and the remaining 75% being venous blood volume.Therefore, rSO₂In fact, it is a weighted average of arterial and venous oxygen saturation in local brain tissue, which is closer to venous oxygen saturation and can reflect the dynamic balance of cerebral oxygen supply and consumption.

Due to the fact that this detection technology does not rely on arterial pulsation, we can measure cerebral oxygen parameters normally even in cases of low blood pressure, deep hypothermia, weak pulse, or even cardiac arrest.

clinical application

Zweifel et al. discovered rSO₂The elevation is consistent with the relief of vascular spasm and the improvement of clinical symptoms. Through arterial imaging, arterial spasm and ipsilateral rSO were observed₂If the decrease is significantly correlated and the degree of spasm increases (especially when the vessel diameter decreases by more than 75%), then rSO on the same side₂Significantly reduced,This indicates that NIRS can synchronously detect cerebral oxygen reduction secondary to vascular spasm and has good sensitivity.McCormick et al. had 7 voluntary participants inhale a low oxygen concentration mixed gas (FiO)₂=7%) causes transient hypoxia, while closely monitoring EEG and SaO₂、SpO₂and rSO₂The changes in various indicators showed that the decrease in cerebral oxygen saturation and the change in inhaled oxygen concentration occurred almost simultaneously, and rSO₂The decrease is about 2 minutes earlier than the change in EEG, proving that NIRS can detect cerebral hypoxia earlier and more sensitively when other monitoring parameters are still within the normal range. Taussky et al. used NIRS and CT perfusion imaging techniques to simultaneously detect cerebral oxygen saturation and local cerebral blood flow in 1287 patients (including subarachnoid hemorrhage, ischemic stroke, and cerebral hemorrhage), and found a good correlation between the two,This indicates that NIRS can serve as an effective, non-invasive, and real-time monitoring tool for cerebral oxygen in intensive care units.

Carotid endarterectomy (CEA) can relieve transient cerebral ischemia of unilateral carotid artery system and eliminate atherosclerotic plaques and ulcers that cause transient cerebral ischemia. During carotid endarterectomy, it is often necessary to clamp one side of the carotid artery. It is crucial to ensure blood supply to the brain area during the procedure. Although the Willis loop of the basilar artery can provide collateral circulation oxygen supply, continuous evaluation and monitoring of the blood flow in the collateral circulation are still necessary.Compared to other methods of cerebral oxygen monitoring, NIRS can provide a more convenient, non-invasive, and continuous implementation of rSO₂Monitoring can effectively prevent perioperative cerebrovascular accidents and even death related to CEA, and is an effective means of predicting cerebral ischemia and hypoxia during CEA surgery.Research finds perioperative rSO in CEA patients₂Comparison of cognitive function and somatosensory evoked potential changes in rSO₂The significance of monitoring somatosensory evoked potentials during CEA surgery,It was found that patients did not experience cognitive impairment during the perioperative period, and when cerebral blood flow reperfusion occurred, rSO₂Compared to changes in somatosensory evoked potentials, it is more significant and very beneficial for observing the blood supply reperfusion status of brain regions during the perioperative period. It is a simple and effective monitoring method for CEA during the perioperative period. It is generally believed that rSO₂A relative decrease of more than 12% indicates cerebral ischemia, warning clinicians to make corresponding pharmacological and physiological interventions.

At present, surgery combined with radiotherapy and chemotherapy is still the most effective treatment for major brain tumors such as gliomas and meningiomas, and the identification of brain functional areas during brain tumor surgery is the key to the success or failure of the surgery.When brain functional areas are activated, the concentration of oxygenated hemoglobin rapidly increases, while the concentration of deoxygenated hemoglobin slowly decreases. By monitoring the changes in hemoglobin in both oxygenated states, the brain functional activity area can be determined. This principle is called the blood oxygen level dependent method (BOLD). Currently, in addition to functional magnetic resonance imaging technology, NIRS technology can also utilize this principle to achieve non-invasive real-time monitoring of brain functional areas.Fujiwaran et al. used NIRS and functional magnetic resonance imaging technology to simultaneously monitor the peritumoral cortex of brain tumor patients and found that due to the influence of tumor lesions, the pattern of hemoglobin concentration changes was abnormal when the peritumoral brain functional areas were activated,Using functional magnetic resonance imaging alone cannot accurately detect brain functional areas, resulting in false negative errors.

summary

The Bolian Zhongke Brain Tissue Oxygen Saturation Monitor MOC200 has complete main parameters and related sub parameter indicators. It adopts advanced NIRS technology and can continuously, real-time, and non-invasive monitor the balance between brain tissue oxygen supply and consumption in patients from three dimensions: real-time trend, relative change, and AUC (depth and time under desaturation state). It can detect and intervene in rSO in a timely manner₂Abnormal conditions can reduce brain damage caused by abnormal cerebral oxygen in patients, shorten hospitalization time, and improve patient prognosis.