Cerebral and peripheral muscle oxygenation and perfusion: Course in moderate and late preterm neonates during the first day after birth.

Aim: To investigate the ratio of cerebral tissue oxygenation index (cTOI) to peripheral muscle tissue oxygenation index (pTOI) measured by near-infrared spectroscopy (NIRS) in cardio-circulatory stable preterm neonates without signs of inflammation/infection on the first day after birth.

Methods: Observational study analysing secondary outcome parameters of the 'Avoiding Hypotension in Preterm Neonates (AHIP)' trial (ClinicalTrials.gov identifier: NCT01910467). Preterm neonates, who had cTOI and pTOI measurements during 24 h after birth, were included. In each neonate the mean of the cTOI/pTOI-ratio, cTOI, pTOI and routine monitoring parameters were calculated for each hour and for the 24-h measuring period. Courses of all measured parameters were analysed.

Results: Eighty-seven stable preterm neonates (33.1 [32.1-34.1] weeks of gestation) were included. The mean value over the 24-h measuring period for the cTOI/pTOI-ratio was 0.96 ± 0.02, for cTOI 70.1 ± 1.4 and for pTOI 73.4 ± 0.9. Routine monitoring parameters were in the normal ranges over 24 h. The courses of the cTOI/pTOI-ratio and cTOI showed significantly lower values from hour 5 to 15 compared to the first hours after birth. Heart rate decreased significantly over time, whereas mean arterial blood pressure increased significantly. pTOI, arterial oxygen saturation and body temperature showed no significant change over time.

Conclusion: We are the first to report on cTOI/pTOI-ratios for cardio-circulatory stable preterm neonates over a 24-h period after birth, showing significantly lower values from hour 5 to 15 compared to the first hours after birth.