The Peripheral(-Muscle) Oxygenation and Perfusion Score (POP-Score): A New Non-Invasive Tool Associated with Elevations in C-Reactive Protein Levels in Neonates

Background/Objectives: Peripheral(-muscle) oxygenation assessed with near-infrared spectroscopy might serve as an early marker of infection/inflammation; however, evidence of its clinical relevance is lacking so far. This study aimed to develop a peripheral(-muscle) oxygenation and perfusion score (POP-Score) using the peripheral(-muscle) tissue oxygenation index (pTOI) combined with non-invasive monitoring parameters within six hours after birth. The POP-Score was designed to explore associations with elevated C-reactive protein (CRP), as an early infection/inflammation marker, in term and late-preterm neonates. Methods: Secondary outcome parameters from a prospective observational study were analysed. Included neonates weighed ≥2000 g with respiratory distress, excluding those with umbilical artery pH < 7.20. Neonates with CRP ≥ 20 mg/L were 1:4-matched to those with CRP < 20 mg/L by gestational age (±2 weeks). For pTOI measurements, a sensor was placed for a duration of 30 s, followed by four further reapplications of the sensor, using the NIRO200NX within the first six hours after birth. The POP-Score was established using the following formula: (pTOI [%] × subcutaneous fat layer thickness [cm] × heart rate [bpm])/(arterial oxygen saturation [%] × systolic blood pressure [mmHg]). POP-Score was correlated with the highest CRP within 48 h. Results: Thirty neonates were included (median gestational age: 39.1 weeks [CRP < 20 mg/L group] vs. 37.3 weeks [CRP ≥ 20 mg/L group], p = 0.299; median birth weight: 3561 g vs. 3260 g, p = 0.058, respectively). Median POP-Scores were significantly different: 1.11 (CRP ≥ 20 mg/L) vs. 0.85 (CRP < 20 mg/L), p < 0.001. POP-Score correlated positively with CRP (r = 0.341; p = 0.070). In this small exploratory cohort, a POP-Score cut-off of 1.00 was associated with CRP ≥ 20 mg/L (100% sensitivity and 87% specificity); however, these estimates are uncertain due to the limited sample size. Conclusions: This study is the first to describe a new score for peripheral(-muscle) oxygenation and perfusion (POP-Score), which may represent a potential approach for early, non-invasive assessment but requires validation in adequately powered studies before any clinical application. Trial Registration: Clinicaltrials.gov, Trial registration number: NCT04818762, Date of Registration: 26 March 2021