Supplementary Material for: Accuracy of a Novel Transcutaneous PCO₂ and PO₂ Sensor with Optical PO₂ Measurement in Neonatal Intensive Care: A Single-Centre Prospective Clinical Trial

Background and Objectives: Transcutaneous PCO₂ and PO₂ measurement systems offer non-invasive blood gas trend monitoring. The aim of this prospective study was to assess bias and precision of a transcutaneous PCO₂ and PO₂ measurement system incorporating a novel pO₂ sensor (Sentec OxiVenT™) in neonates ≥34 weeks of gestational age (GA) admitted to intensive care. Methods: Transcutaneous PCO₂ and PO₂ were compared to arterial and capillary blood gas measurements. Bias and precision were calculated by fitting linear mixed models to account for repeated measurements, and influence of clinical covariates on bias and precision was assessed. Results: We obtained 611 paired transcutaneous and blood gas measurements in 110 patients (median GA 38.3 [interquartile range 36.1–39.7] weeks; age 9 [4–15] days; weight 3,000 [2,500–3,500] g). Transcutaneous PCO₂ showed significant bias to arterial PCO₂ (+0.61; 95% confidence interval 0.46, 0.76 kPa), but not to capillary PCO₂ (−0.23; −0.46, 0.002 kPa). Bias of transcutaneous PO₂ was significant to arterial PO₂ (−2.50; −2.94, −2.06 kPa), while no significant bias compared to capillary PO₂ was observed (+0.17; −0.30, 0.64 kPa). Precision intervals were ±1.8/2.0 kPa for arterial versus capillary PCO₂ and ±4.9/3.3 kPa for arterial versus capillary PO₂ comparisons, respectively. Further, sensor operating temperature (43°C vs. 42°C), soft tissue oedema, vasoactive drugs, weight, and GA significantly altered bias (p < 0.05). Conclusions: The tested transcutaneous blood gas measurement system showed no significant bias compared to capillary PCO₂ and PO₂, acceptable bias to arterial PCO₂, and limited agreement with arterial PO₂. Precision intervals were wide for all comparisons.