Biological Rhythms of Vital Signs in Newborns in a Neonatal Intensive Care Unit: A Prospective Observational Study

To characterize the presence and relationships between the rhythms of axillary temperature, heart rate, respiratory rate, blood pressure, and peripheral oxygen saturation, from the first (D1) to the third day of life (D3) in newborns (NBs) hospitalized in the neonatal intensive care unit (NICU). Primary, descriptive, nested clinical study within a primary, observational, and prospective clinical study, conducted in the NICU of a public hospital in the city of São Paulo, Brazil. Demographic data and vital signs (axillary temperature, heart rate, respiratory rate, blood pressure, and peripheral oxygen saturation) recorded in clinical charts were collected between the first and third day of life (D1-D3) at 4-h intervals (8 h; 12 h; 16 h; 20 h; 24 h; 4 h). The biological rhythms of the vital signs were analyzed using the Cosinor algorithm. Eighty-eight NBs participated (44 preterm and 44 term). Incipient variability of vital signs was observed in the first days, with reduced amplitudes and unstable phases. There was a correlation between the amplitude of axillary temperature and length of hospital stay in preterm infants, and between the amplitude of diastolic blood pressure and length of stay in term infants, suggesting the clinical potential of variability as a marker of neonatal maturation and clinical vulnerability. Altogether, the findings indicate the presence of early physiological rhythmicity and reinforce the importance of chronosensitive care and the incorporation of chronobiological parameters in clinical management, aiming to optimize the development and outcomes of hospitalized newborns.