The incidence of cerebral palsy has not decreased despite advances in neonatal care. Preterm infants are at a high risk of cerebral palsy. Moreover, preterm infants might experience permanent neurological sequelae due to injury in the preterm brain. Although the etiology of preterm brain injury is not fully understood, preterm brain injury is strongly associated with abnormal cerebral perfusion and oxygenation. Monitoring systemic blood pressure or arterial oxygen saturation using pulse oximetry is not enough to guarantee proper cerebral perfusion or oxygenation. Early detection of improper cerebral perfusion can prevent irreversible cerebral damage. To decrease brain injury through the early detection of under-perfusion and deoxygenation, other diagnostic modalities are needed. Near-infrared spectroscopy can continuously and noninvasively monitor regional oxygen saturation (rSO2), which reflects the perfusion and oxygenation status of tissues at bedside. Near-infrared spectroscopy represents a balance between tissue oxygen supply and demand. Cerebral rSO2 monitoring has been used most frequently in neonatal cardiac surgery to monitor cerebral oxygenation and prevent hypoxic damage or shock. Recently, cerebral, renal, or splanchnic rSO2 in neonates is frequently monitored. The progression of a disease, brain injury, and death can be prevented by detecting changes in rSO2 values using near-infrared spectroscopy. In this article, the basic principles, usefulness, and applications of near-infrared spectroscopy in neonates are discussed.
Cerebral palsy occurs in 1 in 500 live births. Its incidence has not decreased despite advances in neonatal care [
Although the etiology of preterm brain injury is not fully understood, it is known that preterm brain injury is strongly associated with abnormal cerebral perfusion and oxygenation [
The brain is an autoregulatory organ. Thus, cerebral blood flow and pressure can be maintained within the normal range by itself, even when there are fluctuations in the systemic blood pressure. However, in severely ill infants and preterm infants with immature cerebral vascular tree, cerebral autoregulation ceases. Therefore, under-perfusion and deoxygenation may occur even if there are only slight fluctuations in the systemic blood pressure, which would result in hypoxic ischemic brain injury [
Near-infrared spectroscopy (NIRS) is a noninvasive technique that can continuously monitor regional oxygen saturation (rSO2), which reflects the perfusion status and oxygenation status of underlying tissues at the bedside [
Near-infrared light (700 to 1,000 nm wavelength) can penetrate living tissues better than visible or ultraviolet light. The light absorption spectra are different between oxygenated and deoxygenated hemoglobin [
In neonates, cerebral, renal, or splanchnic rSO2 is frequently monitored. Cerebral rSO2 is monitored to prevent brain damage in conditions which affect cerebral perfusion and oxygenation. These conditions include hypoxic ischemic encephalopathy, hypotension, apnea and bradycardia, HSDA, ductal closure, and perioperative status of congenital heart disease. Renal or splanchnic rSO2 is monitored to prevent renal or splanchnic underperfusion in infants with necrotizing enterocolitis and those with acute renal failure. Renal or splanchnic rSO2 is also monitored in infants to determine the need for red blood cell transfusion and to monitor response to red blood cell transfusion. There are a number of NIRS devices available for monitoring rSO2 in neonates. These NIRS devices include INVOS 5100 (Somanetics, Troy, MI, USA), Fore-Sight (CAS Medical, Branford, CT, USA), SenSmart X-100 (Nonin Medical, Plymouth, MN, USA), Equanox 7600 (Nonin Medical, Plymouth, MN, USA), and NIRO-200NX (Hamamatsu Photonics, Hamamatsu, Japan), which are commonly used in neonatal intensive care units.
Cerebral rSO2 is usually lower than splanchnic or renal rSO2 because the metabolic activity of and demand for oxygen of the brain are higher than those of other living organs [
Neonates with hypoxic ischemic encephalopathy have increased cerebral rSO2 and decreased cerebral FTOE [
Preterm infants have different cerebral rSO2 baselines at immediate postnatal stage according to gestational age. Preterm infants have increased cerebral rSO2 and decreased cerebral FTOE compared to term infants at birth. The younger the gestational age, the higher the cerebral rSO2 and the lower the cerebral FTOE [
Variations in the cerebral blood flow according to the cerebral perfusion pressure is limited by cerebral autoregulation. Preterm infants are at a high risk of impaired cerebral autoregulation mainly due to immaturity of the cerebral vessels. It has been reported that impaired cerebral autoregulation in preterm infants is highly associated with neonatal death [
Decreased cerebral oxygenation due to HSDA adversely influences brain growth and neurodevelopmental outcome [
There are still controversies about the effect of the closure of ductus arteriosus on cerebral blood flow and cerebral oxygen delivery. Indomethacin decreases cerebral blood flow and cerebral oxygen delivery whereas ibuprofen does not alter cerebral blood flow or cerebral oxygen delivery [
NIRS has been used most frequently for the perioperative monitoring of cerebral oxygenation during neonatal cardiac surgery to prevent hypoxic damage or shock. The decrease in cerebral rSO2 detected using NIRS during operation to treat congenital heart disease is frequent because cardiopulmonary bypass can cause an abrupt change in cerebral blood flow and oxygenation. Therefore, cerebral rSO2 monitoring is required during cardiac surgery to monitor cerebral oxygenation and to prevent hypoxic damage [
Splanchnic rSO2 is usually higher than cerebral rSO2 due to higher metabolic activity in the brain. McNeill et al. [
Necrotizing enterocolitis is one of the most common gastrointestinal morbidities in preterm infants. The pathogenesis of necrotizing enterocolitis is multifactorial. However, intestinal ischemia is known to precede necrotizing enterocolitis. Preterm infants without necrotizing enterocolitis have higher splanchnic rSO2 during the first week of life compared to preterm infants who develop necrotizing enterocolitis later (77.3% vs. 70.7%,
NIRS has been widely used in neonatal intensive care units in Korea by the Korean National Health Insurance since 2018. Health insurance coverage for the somatic rSO2 of high risk neonates in the neonatal intensive care unit includes the following: (1) respiratory distress syndrome requiring ventilator care; (2) HSDA or complex heart disease; (3) shock or sepsis; and (4) hypoxic ischemic encephalopathy according to notification no. 2018-184 of the Ministry of Health and Welfare in September 2018.
NIRS can be used for continuous monitoring noninvasively at the bedside without interrupting the routine care of caregivers. Reference ranges of rSO2 and FTOE are different in different infants. They are also different according to postnatal days even in the same infant. Their values are affected by a lot of variables that can affect the oxygen demand and consumption of tissues, such as the metabolic activity of tissues, fever or hypothermia, perfusion status, blood pressure, and level of hemoglobin, especially in preterm infants with anemia. Specifically, splanchnic rSO2 (infra-umbilical) is affected by sensor position, bladder distension, or urinary catheter. Thus, the interpretation of rSO2 values or FTOE values is controversial, and there are no universally accepted normal values. These limitations of NIRS could be the main obstacle to introduce NIRS as a routine bedside monitoring for neonates. However, there are advantages of NIRS monitoring. Caregivers need to focus on the baseline values and trends of changes in these values to prevent the progression of the disease, brain injury, or death. Further studies with a large number of neonates are required to reach a consensus on the uniform interpretation of the values and to develop universally accepted normal values.
No potential conflict of interest relevant to this article was reported.
Principles of near-infrared spectroscopy. The nearinfrared spectroscopy device emits light from a light emitting diode. These emitted photons can pass through tissues and become absorbed by oxygenated and deoxygenated hemoglobin in living tissues at different ratios according to the oxygenation status of tissues. These photons from the light source can make arc. The non-absorbed fraction of the photons is received by two detectors. The proximal arc detector receives signal from the superficial tissue whereas the distal arc detector receives signal from both the superficial and deep tissues. The proximal value is subtracted from the distal value and the result represents the oxygen saturation (rSO2) at a depth of 1 to 2 cm in the deep tissue.
Cerebral regional oxygen saturation (crSO2) and cerebral fractional tissue oxygen extraction (cFTOE) immediately after birth. (A) The 10th, 25th, 50th, 75th, and 90th percentiles of crSO2 during the first 15 minutes after birth in neonates who do not require medical support. The crSO2 is low at birth. It increases for several minutes and becomes stable. (B) The 10th, 25th, 50th, 75th, and 90th percentiles of cFTOE during the first 15 minutes after birth in neonates who do not require medical support. The cFTOE is high at birth. It decreases for several minutes and becomes stable. Adapted from Pichler et al.21), with permission from Elsevier.