Table 1.

Summary of the available literature on the use of Near Infrared Spectroscopy (NIRS) to measure splanchnic oxygenation in neonates.

Author and reference	Population studied	Study design (including measurement location)	Primary outcomes/findings
Normal ranges of splanchnic regional oxygenation
Cortez et al. (15) (2011)	-n = 21 -preterm infants <30 w GA	-prospective observational cohort study -infants enrolled within 48 h of birth -continuous NIRS probe placed on left paraumbilical region for 14 days	-demonstrated feasibility of using NIRS continuously for 14 days -daily mean rSO2 values decreased over the first 9 days (p < 0.0001) followed by an increase from days 10–14 (p = 0.0061) -infants with feed intolerance had lower splanchnic regional saturations as compared with those tolerating feeds (p = 0.0043)
McNeill et al. (9) (2011)	-n = 14 enrolled but 2 excluded from analysis meaning n = 12 infants’ data used for analysis -healthy preterm infants (29–34w GA)	-continuous monitoring of abdominal (infra-umbilical), cerebral, and renal (right posterior-lateral flank) regional oxygenation using NIRS from the time of birth to 21 days of life -six infants were between 29 and 30 weeks gestation and 6 were between 32 and 33 weeks gestation. Some of the analysis was done in these subgroups	-abdominal regional oxygenation (32–66\%) was lower than cerebral (66%–83%) and renal (64%–87%) -cerebral and renal oxygenation decreased significantly over the first weeks of life (p < 0.01) -abdominal oxygenation decreased over week 1 of life and then increased up to day 21. The median nadir was at day 7 (range 3–9) for those born at 29–30 weeks and day 4.5 (range 3–8) for those born at 32–33 weeks -regional oxygenation variability was lowest for cerebral measurements and highest at the abdomen -abdominal variability decreased significantly over time (p ≤ 0.05)
van der Heide et al. (16) (2021)	-n = 220 -GA <32w and/or BW <1,200 g -excluded those with NEC/sepsis/died	-prospective study -over the first week after birth measured a daily 2 h mean of rsSO2 (infra-umbilical) to assess its associations with sex, GA, postnatal age (PNA), small-for-gestational age (SGA) status, patent ductus arteriosus, haemoglobin, nutrition, and head circumference at birth -used these factors to create a prediction model rsSO2 = 3.2 − 7.0 × PNA + 0.8 × PNA2 − 4.0 × SGA + 1.8 × GA.	-on day 1, the mean ± SD rsSO2 value was 48.2% ± 16.6. The nadir of rsSO2 was on day 4 (38.7% ± 16.6 smoothed line) to 5 (37.4%±17.3, actual data), after which rsSO2 increased to 44.2% ± 16.6 on day 7. -rsSO2 is lower in infants with a lower gestational age and in small-for-gestational age infants -gestational age, postnatal age, and small-for-gestational age status affect regional splanchnic oxygen saturation and need to be considered when interpreting regional splanchnic oxygen saturations using NIRS -authors provided a model so that reference values for infant regional splanchnic oxygen saturation can be computed with a formula: (rsSO2 = 3.2 − 7.0 × PNA + 0.8 × PNA2 − 4.0 × SGA + 1.8 × GA)
Splanchnic NIRS and sepsis
Calderon et al. (17) 2016)	-n = 69 -animal study involving rabbits -14 died, 15 control and 40 in the study group	-used NIRS to measure regional hepatic and splanchnic (infra-umbilical) oxygenation -study group injected with Escherichia coli toxin to see the effect of sepsis on abdominal perfusion and whether NIRS was a valid tool to measure this	-hepatic rSO2 had a significant reduction 60 min after the administration of the toxin (p = 0.034) although not significant when the overall reduction analysed -splanchnic rSO2 decreased earlier from 30 min after the administration of the toxin (p < 0.001)
Splanchnic NIRS and PDA Note other studies in this table comment on impact of PDA on NIRS readings, but was not their primary outcome (therefore this has been highlighted under each study where relevant)
Meier et al. (18) (2006)	-n = 1	-case report -infant with large PDA whose mesenteric (midline abdomen below umbilicus) and cerebral rSO2 were measured pre and post PDA ligation	-pre-PDA ligation the infant had lower cerebral and mesenteric rSO2 which significantly increased post PDA ligation (p < 0.0001)
Petrova et al. (19) (2011)	-n = 38 -preterm infants <32w GA with confirmed PDA on echocardiogram	-prospective cohort study -NIRS used to measure cerebral (rSO2-C), renal (thoracolumbar) (rSO2-R) and mesenteric (midline region below umbilicus) (rSO2 -M) oxygenation for 60 min before pharmacological treatment of PDA	-no significant difference in rSO2-C or rSO2-R irrespective of respiratory support -in Infants with a large PDA on nCPAP, the rSO2-M was lower and mesenteric FTOE higher than those mechanically ventilated and those with moderate PDA -significantly higher proportion of infants with a moderate PDA were mechanically ventilated compared with large PDA group
Splanchnic NIRS and feeding Note other studies in this table comment on effect of feeding on NIRS readings, but this was not their primary outcome (therefore this has been highlighted under each study where relevant)
Braski et al. (20) (2018)	-n = 52 -preterm infants with GA ≤32w and ≤12w of age	-prospective observational two-centre study involving preterm infants who were stable and tolerating enteral feeds -infants had cerebral and splanchnic (infra umbilical) rSO2 measured using NIRS continuously for 24 h -SCOR was subsequently calculated -mean regional oxygenation was calculated for 30 min prior to each feed, for the duration of each feed and 30 min after each feed	-average mean baseline SCOR decreased significantly during feeds (p = 0.043) -no significant difference in cerebral or splanchnic oxygenation during feeds although there was a trend to decreased splanchnic oxygenation during feeds -infants with lowest SCOR pre feeds had the largest decrease in SCOR with feeds
Corvaglia et al. (21) (2014)	-n = 30 -preterm infants <32w GA receiving NGT feeds at more than 100 ml/kg/day	-prospective observational study --cerebral and splanchnic (infra umbilical) oxygenation measured using NIRS for 6 h while the infants had two feeds—one was bolus, and one was continuous feed	-no change in cerebral oxygenation over time regardless of feeding method -significant increase in splanchnic oxygenation after bolus feeds and a reduction in splanchnic oxygenation during continuous feeding (p < 0.0001)
Gillam-Krakauer et al. (22)(2013)	-n = 25 preterm infants less than 14 days of life enrolled but 7 withdrawn so 18 for analysis -GA <31 w -BW <1,500 g	-prospective observational study --measured splanchnic regional oxygenation (infra umbilical using NIRS continuously for 3 days and measured SMA artery velocities using doppler USS --compared change in SMA velocity from immediately before to 10 min and 60–120 min after feeding with change in the abdominal regional oxygenation -Spearman's rank correlation used to see if a significant association existed	-changes in splanchnic regional oxygenation was significantly associated with changes in systolic, diastolic, and mean SMA velocity from fasting to 60–120 min after feeding (p = 0.016, 0.021, 0.010) and from 10 min after a feed to 60–120 min after feeding (p = 0.009, 0.035, 0.032)
Martini et al. (23) (2018)	-n = 20 -preterm infants <34w GA with absent or reversed umbilical EDF Antenatally	-observational pilot study -continuous monitoring of splanchnic oxygen saturation (infra umbilical) (SrSO2) and cerebral oxygen saturation (CrSO2) at enteral feeding introduction until fully enterally fed (≥150 ml/kg/day) -monitoring took place 30 min before feeding until 3 h after feed	--infants who developed gastrointestinal complications later demonstrated significantly lower SrSO2 (p = 0.02)
Studies involving splanchnic NIRS to measure the effect of RBCT/anaemia
Bailey et al. (24) (2010)	--n = 35 infants -preterm infants <37w -at least 5 days old at time of RBCT	-prospective, observational study -simultaneous measurement of cerebral rSO2 and splanchnic (in the midline below the umbilicus and above the pubic symphysis) rSO2 during RBCT (15 ml/kg RBCT given)	-cerebral rSO2 increased after RBCT and remained elevated for 12 h -splanchnic rSO2 also increased following RBCT although this increased after the rise in cerebral rSO2 -no correlation between Hb levels and cerebral rSO2 (r = −0.17, p = 0.36) or splanchnic rSO2 (r = −0.07, p = 0.72) before or following RBCT
Bailey et al. (28) (2012)	-n = 55 -preterm infants in first 5 days of life with Hb ≤11 g/dl	-prospective observational pilot study -measured cerebral and splanchnic oxygenation (just below the umbilicus) and then calculated the CSOR -CSOR was used as a marker for need for RBCT in preterm infants -groups divided into whether they were symptomatic or not from anaemia and whether improved or not after RBCT if it was given	-symptomatic patients who improved following RBCT had a low preceding CSOR (≤0.73) which improved following RBCT (p = 0.03) -symptomatic infants who did not improve following RBCT had higher CSOR values prior to RBCT
Banerjee et al. (64) (2016)	-n = 59 -preterm infants (≤34 w GA)	-prospective observational study -preterm infants receiving RBCT for clinical indication -infants divided into three groups based on postnatal age -a single operator measured the SMA peak systolic and diastolic velocities 30–60 min before and after RBCT -used NIRS with the probes placed in the hypogastrium in the midline above the symphysis pubis to assess splanchnic oxygenation (sTOI) 15–20 min, during and 15–20 min after RBCT	-after RBCT sTOI increased (p < 0.01) and FTOE decreased (p = 0.02) in all groups -sTOI correlated with SMA blood flow
Dani et al. (25) (2010)	--n = 15 -preterm infants <30 w GA	-prospective observational study -NIRS was used to measure cerebral, splanchnic (infra umbilical), and renal (right of midline on the T10-L2 posterior flank) rSO2 during RBCT	-cerebral, splanchnic, and renal rSO2 increased following RBCT -associated decrease in FTOE in symptomatic anaemic preterm infants
Mintzer et al. (26) (2014)	-n = 10 -infants with BW <1,250 g	-observational pilot study -infants enrolled within 72 h after birth and monitored for 7 days -measured cerebral, renal (right flank), and splanchnic (infra umbilical) rSO2 in infants receiving “booster” RBCT -infants with similar VLBW with normal haematocrit and <10 ml/kg blood taken for routine blood samples were used as control infants for comparison	-rSO2 increased and FTOE decreased for each patient following “booster” RBCT (p < 0.05) -in all groups splanchnic rSO2 values were lower than cerebral and renal rSO2 -in all groups cerebral rSO2 was the highest (p < 0.05)
Sood et al. (27) (2014)	-n = 57 -preterm infants -median GA 27 w	-monitored cerebral and splanchnic (infraumbilical) rSO2 in preterm infants receiving RBCTs -defined 3 time points (pre RBCT—12 h prior, during RBCT and post RBCT—24 h after RBCT) and 3 groups (1 = no NEC within 7 days of RBCT, 2 = NEC within 7 days prior and 3 = NEC within 7 days after RBCT) -the 57 infants received 147 RBCTs (Group 1 = 120, Group 2 = 19, and Group 3 = 8)	-in group 1 and 2 rSO2 increased over RBCT periods -in group 3 rSO2 decreased over RBCT periods -RBCT, followed by a diagnosis of NEC, were characterised by lower heart rates pre-, during and post-RBCT, decline in sRSO2 and increase in cFTOE post-RBCT compared to RBCTs not associated with diagnosis of NEC -infants received RBCT who then developed NEC were characterised by higher variability in sRSO2, post RBCT reduction in sRSO2 and lower CSOR values post RBCT compared to pre RBCT

BW, birthweight; CGA, corrected gestational age; crSO₂, cerebral oxygenation; CSOR/SCOR, cerebral splanchnic oxygenation ratio; cTOI, cerebral tissue oxygenation index; ELBW, extremely low birthweight; FTOE, Fractional tissue oxygen extraction; GA, gestational age; Hb, Haemoglobin; HbF, Haemoglobin F; NEC, Necrotising Enterocolitis; NIRS, Near Infrared Spectroscopy; PDA, patent ductus arteriosus; RBCT, red blood cell transfusion; rSO₂, regional oxygenation; SMA, superior mesenteric artery; sTOI, splanchnic tissue oxygenation index; TANEC, transfusion associated NEC; TR-NEC, Transfusion related NEC; VLBW, very low birth weight.