In the neonatal intensive care unit, cardiopulmonary monitoring has become the most basic monitoring, but there is still a lack of monitoring of cerebral oxygen saturation, especially for suspected or diagnosed brain injury patients. Both full-term and premature infants in intensive care units have a high risk of brain damage,During the process of brain injury, changes in brain tissue oxygen occur before electroencephalography, neurological function, and tissue morphology. Monitoring brain tissue oxygen can effectively provide brain protection for critically ill newborns.In 2021, expert consensus proposed that NIRS can evaluate the development and brain damage of newborns, thereby achieving early diagnosis. Changes in cerebral hemodynamics and decreased cerebral oxygen saturation play an important role in the pathogenesis of brain injury in premature infants. The most common brain injuries in premature infants include stromal/intraventricular hemorrhage (GM-IVH), premature white matter injury (WMI), hypoxic encephalopathy (HIE), and brain injuries associated with severe cardiovascular diseases.
1. Equipment and principles
The NIRS monitoring time varies from several hours to several days depending on the condition. Through an optical signal sensor placed on the head, near-infrared light of different wavelengths is transmitted through the skin and skull to the brain tissue. In the brain tissue, the light is mainly absorbed and scattered by oxygenated hemoglobin (HbO2) and deoxyhemoglobin (Hb), which have different absorption modes due to their different wavelengths. The value is obtained by analyzing the light returned to the device sensor. The near-infrared spectrometer uses the above two measurement parameters to calculate the local oxygen saturation (rSO2) value of brain tissue, also known as tissue oxygenation index (TOI). RSO2 reflects the oxygenation status of cerebral blood vessels 2-3cm below the sensor. The brain tissue is densely covered with numerous microvessels, including microvessels, arterioles, and capillaries. Cerebral oxygen saturation is actually the mixed oxygen saturation of local cerebral hemoglobin, mainly representing venous blood (70%), reflecting the oxygen supply and metabolism of brain tissue. The increase in rSO2 may be due to an increase in O2 transport, which may reflect an increase in cerebral perfusion or an increase in O2 content in the blood, or a decrease in O2 extraction, and vice versa.
2. Application of cerebral oxygen saturation monitoring in premature infant brain injury
With the popularization of neonatal intensive care technology, the survival rate of premature infants has significantly increased. Approximately 45% of cerebral palsy, 35% of visual impairment, and 25% of cognitive and hearing impairment in children can be attributed to premature birth. The younger the gestational age of premature infants, the higher the risk of poor neurological development outcomes. Studies have shown that changes in rSO2 and inhaled oxygen concentration occur almost simultaneously, 113 ± 59 seconds earlier than EEG changes, and can early identify whether brain tissue is hypoxic. The sensitivity, specificity, and accuracy of NIRS in diagnosing neonatal hypoxic-ischemic encephalopathy are 85.72%, 91.49%, and 90.74%, respectively. The sensitivity, specificity, and accuracy of SpO2 are 50%, 86.96%, and 81.49%, respectively. Therefore, it can be concluded that the sensitivity, specificity, and accuracy of NIRS in diagnosing HIE are higher than those of SpO2. A study conducted continuous 3-hour rSO2 monitoring on 63 premature infants without severe brain injury (gestational age<32 weeks or weight<500g) before discharge. A significant correlation was observed between rSO2 and developmental quotient (DQ) at 6 months, but it was not significant in subsequent (12, 18, 24 months) psychomotor assessments, indicating that rSO2 has short-term predictive value. RSO2 can objectively evaluate the actual oxygenation status of brain tissue, providing objective and quantitative basis for assessing the degree of brain injury in HE children.2.1 Application of cerebral oxygen saturation monitoring in preterm infants with patent ductus arteriosusThe ductus arteriosus is connected between the aorta and the pulmonary artery and near the left pulmonary artery. It is an important channel for fetal circulation. At present, patent ductus arteriosus (PDA) means that the ductus arteriosus remains open for more than 72 hours after birth. The smaller the gestational age of preterm infants, the higher the incidence rate. Hemodynamically significant patent ductus arteriosus (hsPDA) is associated with decreased cerebral perfusion and even intraventricular hemorrhage, leading to long-term neurological developmental delay. In addition to its impact on the respiratory and circulatory system, PDA also exhibits the phenomenon of "catheter theft", causing a redistribution of pulmonary systemic blood volume. It diverts blood from the brain, mesentery, and kidneys to the lungs, leading to pulmonary congestion and a decrease in systemic blood volume, thereby inducing various diseases. A study on rSO2 in 123 premature infants found that rSO2 was reduced, brain oxygen extraction was increased, and FROE was elevated in children with hsPDA. After hsPDA was turned off, rSO2 significantly increased and FTOE significantly decreased, suggesting that PDA closure can alleviate cerebral hypoxia. From this, it can be seen that NIRS is expected to become a routine monitoring method for the treatment of premature infants with hsPDA.
2.2 Predictive value of cerebral oxygen saturation monitoring in intracranial hemorrhage of premature infantsPeriventricular intraventricular hemorrhage (PIVH) is the most common type of bleeding in premature infants and an important cause of neurodevelopmental disorders. Hypoperfusion is considered the main risk factor for PIVH or periventricular white matter injury (PVL). The automatic regulation of cerebral blood flow in premature infants is not yet mature, and unstable cerebral blood flow and intracranial pressure leading to small vessel rupture and bleeding are the direct causes of intracranial hemorrhage in premature infants. The stable state of cerebral blood flow is related to multiple links before, during, and after childbirth, such as the treatment and medication of maternal complications, postnatal rescue processes such as hypoxemia, hyperoxia, hypercapnia, hypocapnia, rapid and excessive infusion, blood pressure and temperature fluctuations, etc. There are studies suggesting that three-dimensional cranial ultrasound and functional near-infrared spectroscopy are of great significance for monitoring intraventricular hemorrhage and post hemorrhage ventricles in premature infants. They are promising bedside monitoring tools that can provide clinical physicians with more information on the structure and function of the newborn brain. RSO2 monitoring of 62 premature infants (gestational age<28 weeks) within 48 hours of birth revealed that rSO2 levels in GM/IVH infants were significantly lower than those in infants without concomitant GM/IH. Compared with healthy premature infants, premature infants with IVH or PVL weighing less than 1500g have lower rSO2 within 72 hours of birth, and the maximum difference in cerebral oxygen saturation occurs within the first 3 hours of birth. Low perfusion reperfusion injury is an important factor in the pathogenesis of IVH. The above studies indicate that cerebral perfusion may decrease before IVH/PVL occurs. However, further research is needed to determine the normal range of rSO2 and guide clinical development of specific intervention measures through rSO2 monitoring, thereby reducing the occurrence and severity of brain injury in premature infants.2.3 The effect of red blood cell transfusion on cerebral oxygen saturation in premature infantsAnemia is a common complication in premature infants. When a child develops anemia, the tissue's oxygen carrying capacity decreases. When it is below a certain level, all organs in the body can be in a relatively hypoxic environment, and in severe cases, it can cause brain damage. Transfusion of red blood cells is still a widely used and effective method for correcting anemia in premature infants in clinical practice. However, there are certain risks associated with blood transfusion, such as transfusion reactions, infectious diseases, transfusion related neonatal necrotizing enterocolitis, intracranial hemorrhage, etc. Therefore, blood transfusion has certain limitations. There are studies showing that transfusion of red blood cells can improve brain tissue oxygenation in premature infants, especially in severely anemic premature infants. At the same time, it is pointed out that using NIRS monitors for brain tissue oxygenation monitoring can determine whether the child's brain tissue is hypoxic, further clarifying whether the child needs red blood cell transfusion. A study of 160 premature infants showed that after receiving red blood cell infusion, the rSO2 level of premature infants increased and the oxygen uptake fraction (FTOE) level decreased, indicating that premature infants have increased oxygen carrying capacity and oxygen transport capacity after red blood cell infusion, which greatly improves the brain tissue oxygenation function of the children. The above research indicates that cerebral oxygen has a good guiding role in the clinical management of anemia in premature infants, providing clinical basis for premature infant blood transfusion guidelines.
2.4 Effects of different ventilation methods and neonatal respiratory distress syndrome on cerebral oxygen saturation in premature infantsMechanical ventilation has a significant impact on cerebral hemodynamics in premature infants and is associated with poor long-term neurological outcomes. A study has shown that premature infants with neonatal respiratory distress syndrome can upregulate rSO2 during pulmonary surfactant therapy with both mechanical and manual ventilation. However, the complications of manual ventilation are higher, mainly manifested by a higher incidence of intracranial hemorrhage, and there is no difference in long-term efficacy between the two. Zheng Wei's study on 49 premature infants showed that the treatment of neonatal respiratory distress syndrome (RDS) with pulmonary surfactant resulted in an increase in rSO2 and a decrease in FTOE during the treatment period. FTOE represents brain oxygen utilization rate, while a decrease in FTOE represents a decrease in brain tissue oxygen utilization. This indicates that the use of PS therapy for RDS premature infants results in an increase in brain oxygen supply over utilization, thereby improving brain tissue oxygen supply in premature infants. Both mechanical ventilation and PS replacement therapy can have an impact on the cerebral hemodynamics of premature infants, and the long-term effects on the nervous system caused by significant changes in cerebral oxygen metabolism also need further observation. Therefore, it can be seen that minimizing changes in cerebral oxygen metabolism during mechanical ventilation and PS replacement therapy highlights the importance of cerebral oxygen monitoring during RDS treatment.The monitoring value of 2.5 cerebral oxygen saturation in the occurrence of brain injury in other neonatal diseases or eventsCompared with SPO2, FTOE monitoring is more valuable in preventing severe retinopathy of prematurity (ROP), and NIRS may become a feasible alternative technology to target SPO2 guidelines. Apnea refers to the absence of respiratory movement for a period of time. If the duration of respiratory arrest is greater than 20 seconds, accompanied by a decrease in heart rate of less than 100 beats per minute or the appearance of cyanosis and decreased blood oxygen saturation, it is called apnea and is more common in premature infants. A study using NIRS technology monitored 329 premature infants with apnea and found a significant correlation between rSO2 and SPO2 during episodes of apnea. Monitoring also revealed that rSO2 appeared earlier than SPO2. When premature infants experienced periodic breathing, SPO2 remained within the normal range and rSO2 decreased significantly.Therefore, it can be concluded that rSO2 is more effective than SPO2 in objectively evaluating the cerebral oxygen status of premature infants during respiratory pauses. A study on 52 cases of severe neonatal hyperbilirubinemia in China showed that the increase in rSO2 during exchange transfusion was greater than that of SPO2. Therefore, it can be inferred that NIRS can monitor the improvement of cerebral oxygenation during neonatal exchange transfusion and avoid the occurrence of cerebral hypoxic injury during the process. When premature infants suffer from severe respiratory and circulatory system diseases or multiple organ failure, oxygen carrying or insufficient blood supply in the circulation can lead to a decrease in cerebral oxygen saturation, resulting in brain damage. Many clinical events, such as neonatal delivery and resuscitation, tracheal intubation, sputum aspiration, intravenous nutrition, nursing procedures, etc., can affect changes in cerebral blood flow, which in turn can affect changes in cerebral oxygen and potentially cause brain damage in premature infants.In summary, NIRS technology has the characteristics of fast, reagent free analysis, high safety and efficiency, and low cost, and has become one of the most effective and promising analytical techniques, increasingly favored by clinical physicians.NIRS technology for monitoring brain tissue oxygen in premature infants can more objectively and accurately reflect the actual situation of brain tissue oxygen compared to traditional SPO2. Especially when the child is complicated with periventricular intraventricular hemorrhage, patent ductus arteriosus, RDS and other diseases, it provides valuable information on brain oxygen metabolism for clinical practice, thereby guiding early intervention measures.
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.
