This is a prospective, single-center Phase II observational study investigating the predictive value of the "Peripheral(-muscle) Oxygenation and Perfusion Score" (POP-Score), a novel non-invasive composite index, for early detection of infection/inflammation in neonates. The POP-Score combines peripheral muscle oxygenation measured via near-infrared spectroscopy (NIRS) with routinely monitored clinical parameters (heart rate, oxygen saturation, systolic blood pressure, and subcutaneous fat thickness). The study aims to determine the optimal cut-off value of the POP-Score measured within the first 6 hours after birth to predict elevated C-reactive protein (CRP ≥20 mg/L) within 48 hours. Additionally, multi-site NIRS measurements (cerebral, peripheral muscle, intestinal, and flank) will be evaluated to assess their association with inflammation. The study includes term and moderate-to-late preterm neonates (birth weight ≥2000g) with respiratory distress, admitted to the neonatal intensive care unit at the Medical University of Graz.

Early identification of neonatal infection and inflammation remains a major challenge in neonatal intensive care, particularly in term and moderate-to-late preterm infants with respiratory distress. Current diagnostic approaches rely heavily on clinical symptoms and laboratory markers, which may be subtle or delayed. This study evaluates the diagnostic potential of a novel, non-invasive scoring system-the Peripheral(-muscle) Oxygenation and Perfusion Score (POP-Score)-in predicting elevated C-reactive protein (CRP) levels (≥20 mg/L) within 48 hours after birth.

The POP-Score integrates near-infrared spectroscopy (NIRS)-based peripheral muscle tissue oxygenation measurements (pTOI) with standard clinical monitoring parameters: arterial oxygen saturation (SpO2), heart rate (HR), systolic arterial blood pressure (SABP), and subcutaneous fat layer thickness (measured by ultrasound). A pilot study demonstrated that a POP-Score >1.00 within 6 hours after birth had high sensitivity (100%) and specificity (87%) in predicting elevated CRP values, suggesting potential for early infection screening.

This is a prospective, single-center, observational Phase II study conducted at the Division of Neonatology, Department of Pediatrics and Adolescent Medicine, Medical University of Graz, Austria. Term and moderate-to-late preterm neonates (birth weight ≥2000g) with respiratory distress and risk factors for infection are eligible. Exclusion criteria include severe congenital anomalies, birth weight <2000g, age >6 hours at time of consent, or umbilical artery pH <7.20.

NIRS measurements will be performed within the first 6 hours after birth at four anatomical sites: peripheral muscle (right forearm), cerebral (left forehead), intestinal (infraumbilical), and flank (left posterior flank at T12-L2). Each site will be measured five times using short-duration sensor reapplications to improve data precision. Concurrently, SpO2 and HR (via pulse oximetry), blood pressure, temperature, and subcutaneous fat thickness (via ultrasound) will be recorded. CRP and other laboratory parameters (including leukocyte count, IT-ratio) will be obtained as part of routine care on the first and second day after birth.

The primary aim is to identify the optimal cut-off level of the POP-Score, calculated within the first 6 hours, to predict CRP ≥20 mg/L within 48 hours. Receiver Operating Characteristic (ROC) analysis will be used, with the area under the curve (AUC) estimated and the optimal cut-off determined via the Youden Index.

Secondary aims include evaluating whether multi-site NIRS measurements (cerebral, peripheral muscle, intestinal, and flank) differ significantly between neonates with CRP ≥20 mg/L and those with CRP <20 mg/L, potentially offering additional early indicators of infection or inflammation.

The target sample size is 93 neonates, assuming a 20% incidence of CRP ≥20 mg/L. This allows estimation of the AUC with a 95% confidence interval and acceptable precision. Data will be analyzed using appropriate statistical tests for categorical and continuous variables. Statistical analyses will be conducted in cooperation with the Institute for Medical Informatics, Statistics, and Documentation, Medical University of Graz.

The POP-Score and multi-site NIRS monitoring offer a potentially powerful, non-invasive approach for early identification of at-risk neonates, enabling earlier intervention and improved outcomes. If validated, this tool may support more accurate and timely clinical decision-making in neonatal intensive care settings.

Inclusion Criteria:

• birth weight ≥ 2000 grams
• Signs of respiratory distress at time-point of inclusion (tachypnoea >60/min, grunting, intercostal/subcostal/jugular retractions, nasal flaring, supplemental oxygen or respiratory support)
• Decision to conduct full life support
• Written informed consent obtained within the first 6 hours after birth, before inclusion in the study
• Age < 6 hours

Exclusion Criteria:

• No decision to conduct full life support
• No written informed consent
• Birth weight < 2000 grams
• Age > 6 hours
• Severe congenital malformations,
• Umbilical cord artery pH <7.20

Term and moderate-to-late preterm neonates (birth weight ≥ 2000 grams) with signs of respiratory distress within the first 6 hours after birth, admitted to the neonatal intensive care unit at the Medical University of Graz. All participants must have a gestational age allowing for clinical stability and must meet inclusion criteria including full life support decision and informed consent obtained within 6 hours of birth.