Stroke is an acute, focal neurological dysfunction caused by central nervous system vascular injury, divided into hemorrhagic stroke and ischemic stroke. Among them, ischemic stroke accounts for about 85%, and is more closely related to neurological damage such as dementia development, cognitive decline, and recurrent stroke. Patients with concomitant ischemic stroke during the perioperative period are more likely to develop perioperative neurocognitive disorders (PNDs) after experiencing a second cerebral blow caused by surgery. PND includes all perioperative cognitive function changes that occur before and within 12 months after surgery, including postoperative delirium (POD), postoperative cognitive dysfunction (POCD), etc. The clinical manifestations of PND patients are varied and the condition is prone to fluctuations. There are many related risk factors, and there is currently a lack of specific methods for treating PND. Therefore, prevention of PND is very important.Regional cerebral oxygen saturation (rS02), as a brain function monitoring technique, is widely used during the perioperative period to monitor cerebral blood flow and oxygenation status. It can warn of adverse neurological complications and help implement timely brain protection measures, which is expected to reduce the incidence of PND.Therefore, this review aims to summarize the current research progress on rS02 monitoring and PND in stroke patients.
The relationship between perioperative stroke and PND
1.1 Overview of perioperative stroke Perioperative stroke is defined as an ischemic or hemorrhagic cerebrovascular accident that occurs during or within 30 days after surgery, and the incidence rate is about 0.1%~8% [3]. Ischemic stroke can be further divided into overt stroke and occult stroke. In the 2013 guidelines of the American Heart Association/American Stroke Association, occult stroke was classified separately and defined as a single or multiple ischemic brain lesions with no clinical symptoms of neurological impairment or neurological impairment unrelated to ischemic lesions, but with CT showing acute abnormal DWI manifestations of focal low-density areas, low T1/FLAIR signal, high T2 signal, ischemic volume ≥ 3mm, located in the cortex or subcortical region. With the development of neuroimaging technology, more and more hidden strokes are being discovered. The diagnosis of overt stroke requires that the clinical symptoms of nerve damage persist for more than 24 hours. Perioperative occult stroke has a higher incidence rate than dominant stroke and is closely related to the type of operation. The incidence of overt stroke during the perioperative period in patients undergoing cardiovascular surgery is 2.4%, while the incidence of occult stroke is as high as 31%. Even in non heart and large vessel surgery, the incidence rate of perioperative occult stroke in elderly patients over 65 years old also reached 10% [6]. Therefore, it can be seen that the high incidence rate of perioperative occult stroke can not be ignored, coupled with the lack of clear medical history and clinical symptoms, has great potential harm.
1.2 The relationship between perioperative stroke and PNDLewis et al. found that there was no significant correlation between postoperative occult stroke and cognitive impairment in cardiac surgery patients one month after surgery [7], but stroke patients after aortic valve replacement were more likely to experience cognitive decline 90 days after surgery [8]. It can be seen that in cardiac surgery research, there are still differences in postoperative cognitive abilities at different time endpoints after stroke. PND has a follow-up period of up to one year, and the cognitive function characteristics of patients at different time stages still need further research. In terms of non cardiac surgery, a multicenter, prospective study enrolled 1116 patients over the age of 65, and the results suggest that perioperative occult stroke is associated with an increased risk of POD and cognitive decline one year after surgery. However, there is still research significance for specific types of non cardiac surgeries, including abdominal surgery, thoracic surgery, orthopedic surgery, and other surgical types that indicate high risk of PND, but there is still a lack of large sample clinical randomized controlled trial data.Application of rSO2 monitoring in stroke patients
RSO2 based on near-infrared spectroscopy technology is commonly used for intraoperative dynamic monitoring due to its non-invasive, continuous, and real-time feedback characteristics. Near infrared light has good penetration through human tissues. Oxyhemoglobin and reduced hemoglobin in human tissues can absorb near-infrared light. By using the difference in absorption coefficients between the two, brain tissue oxygen parameters can be calculated. Brain blood oxygen monitoring can indicate abnormal brain oxygenation status and prompt treatment. RSO2 is the result of balanced oxygen supply to the brain and can indirectly reflect the functional status of stroke patients.The study on the changes of time-domain NIRS after acute ischemic stroke (AIS) shows that the deoxyhemoglobin and total hemoglobin content in the ischemic area increase, while the tissue oxygen saturation in the reperfusion area decreases. This may reflect the hemodynamic compensation of ischemic damaged brain tissue and the metabolic activity of rescued brain tissue [10]. The method of measuring cerebral venous oxygen saturation based on magnetic resonance cerebral oxygen metabolism imaging can serve as an important imaging indicator for evaluating the disease status and early prognosis of AIS [11]. also,RSO2 can be used to assess the situation of vascular occlusion, thrombectomy, and recanalization. In addition to the diagnosis and treatment of stroke, risk prediction has always been a clinical focus.The asynchronous recovery of rSO2 in both hemispheres after neonatal stroke is associated with an increased risk of cognitive impairment [2]. The decrease of rSO2 on the bleeding side by more than 20% compared to baseline in patients with aneurysmal subarachnoid hemorrhage is associated with lower postoperative cognitive function recovery scores [13]The relationship between perioperative rSO2 monitoring and PND
3.1 Relationship between preoperative rSO2 monitoring and PNDThe normal rSO2 is 60%~80%, while heart disease patients may have it as low as 55%~60% [14]. Although there are significant differences in preoperative rSO2 levels among individuals, it can provide important clues to the physiological or pathological status of patients. The latest research indicates that age, gender, and baseline hemoglobin are significant predictors of baseline rSO2. Female and elderly patients have lower rSO2 levels [15]. Some scholars have suggested that low rSO2 may indicate poor preoperative cognitive reserve in elderly patients [16]. A systematic review and meta-analysis indicate that preoperative low rSO2 expression increases the risk of POD [17]. Scholars further calculated that preoperative rSO2 less than 59.5% is a predictive value for POD in patients after cardiac surgery [18]. In addition, patients with POCD after hip fracture surgery are more likely to have preoperative low rSO2 [19].3.2 Relationship between intraoperative rSO2 monitoring and PNDLim et al. conducted an observational study involving 1439 non extracorporeal circulation patients undergoing coronary artery bypass grafting and found that a decrease in rSO2 during surgery was associated with an increased risk of POD [20]. Some studies found that rSO2 levels below 65% during single lung ventilation remained below 65% for more than 3 minutes, leading to a significant reduction in cognitive function recovery in the early postoperative period (within 3 hours after surgery) and a 3-fold increase in POD risk (within 3 days after surgery) [211]. However, another study on single lung ventilation found that bilateral rSO2 levels were not related to POD [2]. There is no consensus on the relationship between the absolute value of rSO2 during surgery and PND. It is considered to be related to the following factors: firstly, rSO2 is influenced by both anatomical and surgical factors. Anatomical factors such as changes in thickness of extracranial tissues, skull, and cerebrospinal fluid [23], as well as dynamic factors that vary with the surgical process, including arterial blood carbon dioxide partial pressure, adjustment of anesthesia ventilation plan (inhaled oxygen concentration and/or end tidal carbon dioxide), intraoperative hemodynamics, and positional changes [24]. Secondly, the performance of measuring equipment also has an impact on parameters.Therefore,The relative trend of rSO2 may be a more important indicator, and continuous monitoring and dynamic comparison can more accurately guide clinical decision-making.In elderly patients undergoing cardiac surgery, intraoperative rSO2 levels below 50% of baseline are associated with POD. During single lung ventilation, patients measured rSO2 on the forehead. Left rSO2 below 90% baseline value (lasting for more than 15 seconds) and right rSO2 below 85% baseline value (lasting for more than 15 seconds) were significantly correlated with POD [22]. Elderly patients undergoing orthopedic surgery with low cerebral oxygen saturation load (defined as the cumulative area under the time rS02 curve) below 10% baseline and 20% below baseline are significantly correlated with postoperative POCD at 3 months [14]. However, Holmgaard et al. conducted long-term follow-up on 148 postoperative cardiac patients, and the results showed that there was no significant correlation between intraoperative rSO2 reduction of 10%, 20%, and duration compared to baseline values and the occurrence of POCD at discharge and 3 months after surgery [26]. The different conclusions drawn from two studies suggest that surgical type may be one of the factors affecting rSO2 changes, and future clinical studies of different surgical types are needed to verify the conclusions. In addition, the academic community often uses rSO2 values<50% or a decrease of>20% from baseline as intervention values. The relationship between rSO2 changes and PND will further guide us to consider the necessity and rationality of intervention measures to reduce rSc0.
3.3 Relationship between rSO2 Joint Monitoring and PNDBased on near-infrared spectroscopy technology, derivative monitoring emphasizes joint monitoring, individualized management of blood pressure, and reduces neurological complications [27]. The commonly used reference method closely related to cerebral oxygen saturation index (COX) and cerebral autoregulation (CA) function. CA is a protective mechanism that regulates cerebral vascular resistance within a certain range of changes in cerebral perfusion pressure, maintaining stable cerebral blood flow without being passively affected by blood pressure [28]. CA damage may be an important mechanism for perioperative stroke and PND occurrence [29]. Simply put, CA means calculating the correlation coefficient between rSO2 and mean arterial pressure (MAP), ranging from -1 to 1. A COX close to 1 indicates loss of CA, while zero or negative correlation indicates intact CA. The blood pressure corresponding to the minimum COX value represents the optimal MAP with minimal changes in cerebral blood flow. Previous research has found that intraoperative CA monitoring can early predict cerebral hypoperfusion in patients with preoperative neurological disorders undergoing surgery [31]. Nowadays, brain protection strategies guided by rSO2 have gradually matured, with the core being to increase oxygen supply and reduce oxygen consumption. Increasing oxygen supply includes maintaining cardiac output and MAP, blood transfusion, and maintaining normal end tidal carbon dioxide partial pressure; Reducing oxygen consumption, including temperature management, analgesia and sedation, prevention of seizures, etc. [32] Previous studies have shown that blood pressure management targeting COX can reduce the incidence of PND [32].At present, perioperative stroke research focuses on the prevention of postoperative stroke, but there is little research on the postoperative cognitive outcomes of patients with preoperative stroke.Exploring the relationship between preoperative stroke and PND is actually a preoperative risk stratification, timely identification of high-risk populations with fragile brain function, early prevention, timely intervention, and standardized nursing.
The Bolian Zhongke MOC series brain tissue oxygen saturation monitor can provide continuous, real-time, and non-invasive monitoring values of tissue oxygen saturation (rSO2), which can reflect specific organs (such as the brain, mesentery, kidneys, etc.) and systemic perfusion status. Research has shown that rSO2 monitoring can detect perfusion damage in the early stages that cannot be detected by conventional hemodynamic detection methods. It can timely monitor the oxygen supply and demand balance of brain and regional tissues, dynamic changes in cerebral blood flow, evaluate brain and tissue ischemia and hypoxia early, guide perioperative management, reduce the incidence of perioperative complications, sensitively reflect the oxygenation status of tissues and intervene, optimize the entire clinical treatment management, shorten hospitalization time, and improve patient prognosis.
