The NIRS technology is approximately 45 years old and there is an increasing interest to use NIRS in the first few minutes after birth. NIRS-measured CrSO₂ and preductal SpO2 monitoring can guide oxygen supply and the medical support during neonatal transition.(1) Cerebral regional oxygen saturation values can be maintained between 10th and 90th centile, thus preventing hypoxic and hyperoxic brain injury. (6)
The first prerequisite for use of NIRS as a guide for intervention needs during resuscitation is establishing normal ranges for regional oxygenation metrics in first 10 minutes after birth.
Cerebral regional oxygen saturation (crSO₂) reading was obtained within the first minute of life and gradually increased through the first 10 minutes and in contrast cerebral fractional oxygen extraction gradually decline through the first 10 minutes after birth. Median reading (10th -90th centile) for crSO₂ are 44.5% (19.6-64) at 1 minute, 72.5% (57-82.9) at 5 minutes and 83% (72-89) at 10 minutes while median vaues (10th -90th centile ). For cFTOE measure are 0.44(0.18-0.73) at 1 minute, at 5 minutes 0.18(0,1-0,35) and at 10 minutes 0.13(0.07-0.25).
Median crSO₂ readings in our study are similar to those established by Gerhard Pichler et al (2013) in term neonates who did not need a respiratory support with NIRS device (INVOS 5100). Median readings obtained in their study were 41% (23–64) at 2 minutes, 68% (45–85) at 5 minutes and 79% (65–90) at 10 minutes.(7)
Nastase L study (2017) used the same criteria with the same NIRS device ( INVOS 5100) and median crSO₂ readings were 35% (15-58.2) at 1 minute, 64%(46.2-85) at 5 minutes and 76% (67.6-87.4) at 10 minutes.(8)Higher 1 minute readings of crSO₂ in our study might be attributed to maternal exposure to 40% oxygen through face mask during cesarean section and this was not mentioned in Nastase L study.
Ranges of crSO₂ may vary according to several factors such as the NIRS device used, gestational age, and need for respiratory support. Cerebral oxygenation measures vary according to the used NIRS devices as the calculated values are determined by different algorithms used by competing vendors.(6) Brain oxygenation metrics are higher among the preterm infants and this is mostly due to impaired cerebral autoregulation in preterm neonates and the different ability of brain tissue to extract oxygen as explained by Lucia Gabriella (2009).(9) Also neonates who need respiratory support have a compromised cerebral tissue oxygenation compared to those without disturbed transition. This difference indicates that decreased crSO₂ in neonates with respiratory support maybe due to decreased arterial oxygen saturation levels and compromised perfusion as found by Schwaberger B (2014).(10) Those factors won’t affect readings in the current work as we included only healthy, full term neonates monitored with the same device. In order to discover other factors that might affect cerebral oxygenation in healthy full term neonates we used 50th centile values to divide patients into high and low norms. Then we constructed logestic regression models to discover the significant predictors of low and high norms. The only significant factor was the mode of delivery at 5 and 10 minutes. Therefore, we divided the patients into C-section and NVD groups and compared them as regard different clinical and oxygenation parameters.
Preductal Oxygen saturation (SpO₂) measures were compared at 1, 5 and 10 minutes of life in patient delivered vaginally or by cesarean section table 5. Oxygen saturation at the first minute showed no statically significant difference between the 2 studied groups (p=0.146). This might be attributed to maternal oxygen administration through face mask with FIO₂ [fractional extraction of oxygen) 40% which reported in all cases during cesarean delivery. While, the difference in SpO₂ at 5 and 10 minutes were statically significant between the normal vaginal and the cesarean groups (p=0.001, p=0.031 respectively). This is might be secondary to the delayed clearance of fetal lung fluid during cesarean delivery.(11)
Regional cerebral oxygenation (crSO₂) was recorded during the first 10 minutes of life simultaneously with peripheral arterial oxygen saturation through pulse oximeter. Table (5) showed NIRS readings for crSO₂ at 1,5 and 10 minutes of life and compared between the patients delivered by CS and NVD. Several studies were different regarding the effect of the mode of delivery on crSO₂.(8, 12, 13) In the present study, there was no statically significant difference regarding crSO₂ at the first minute (p=0.213) between the normal vaginal and the cesarean groups in contrast to Nastase L et al (2017) study.(8) This might be attributed to maternal administration of oxygen through face mask during cesarean section which may raise fetal oxygen saturation at birth. Reginal oxygenation metrics (CrSO₂) at 5 and 10 minutes showed statically significant difference between the patients in patient delivered vaginally or by cesarean section. Average crSO₂ reading of normal vaginal group at 5 minutes was 74.67% vs 66.37% in the cesarean group (p=0.001) while average NVD group reading at 10 minutes was 84.13% vs 78.37% in the CS group (p=0.001) similarly found by Nastase L et al (2017) and in contrast to Gerhard Pichler et al ( 2013) and Berndt Urlesberge et al (2011).(13, 14) The rate of rise from 1 to 5 minutes of life was statically significantly higher among the vaginal group (36%) than the cesarean group (22%) with p<0.001.
FTOE indicates an increase of oxygen consumption due to increased cerebral metabolic rate, decreased oxygen delivery or both.(15) Fractional tissue oxygen extraction at 1, 5 and 10 minutes were calculated and compared between the patients delivered vaginally or by cesarean section. Despite crSO₂ was not different in the 2 groups, FTOE at 1 minute showed a near significant difference between the 2 groups with median value (0.38) in the cesarean group and (0.52) in the normal vaginal group(p=0.07 in patient delivered vaginally or by cesarean section, respectively. FTOE considerably decreased at 5 and 10 minutes and showed statically significant difference between the 2 groups (p=0.005, p=0.004 respectively), in agreement with Nastase L study (2017).(8)
Better cerebral oxygenation metrics and preductal peripheral oxygen saturation were found in vaginal than cesarean group that might be attributed to higher cerebral blood flow due to higher level of carbon dioxide which is the most potent cerebral vasodilator. (8)Another contributing factor is that the vaginally delivered newborns showed a significantly higher catecholamine levels at birth in comparison with those born by cesarean section as found by Kenichi Isobe et al (2002).(16) Released catecholamines act to constrict the peripheral vessels thus increasing the cerebral blood flow. In addition, there is more rapid clearance of fetal lung fluids in the normal vaginal group.
It is logic that there must be correlation between SPO2 and cerebral oxygenation parameters (crSO2 and FTEO). However, their relationship is not constant at 1, 5 and 10minutes. The most significant correlations were at 5minutes SPO2 and cerebra oxygenation parameters (crSO2 and FTEO) with r=0.6 and r=0.4, respectively.
The discrepancy in the strength of correlation could be explained by the following factors: first; crSO₂ reaches the plateau earlier than the peripheral arterial saturation (SpO₂) and the preferential oxygen delivery to the brain during the first few minutes after birth.(15) Second; the cerebral vascular bed constricts after 5 minutes in response to the postnatal rise in the blood oxygen content to protect the brain from excessive oxygen exposure.third; Kehrer M et al (2005) suggested by that the increasing left-to-right shunt through the patent ductus arteriosus together with an inadequate compensatory increase in left ventricular output might decrease the cerebral blood flow .(17)
The limitations of this work is the small sample size the major point of strength that it is the only known published data and centiles abut NIRS monitoring in neonatal transition from developing countries.