Quantifying physiological vital sign differences in newborns from 34+0/7 weeks of gestation and establishment of vital sign reference ranges for the late preterm population

Background: To ensure continued adaptation to extra-uterine life, all newborns have their physiological vital signs monitored intermittently post birth until discharge; these are tracked against pre-defined ‘normal’ reference ranges. Ascertaining an evidence base for ‘normal’ reference ranges is important for the early detection of deterioration in this population, who are at risk of not adapting to the extra-uterine environment due to being born prior to term. Aim: The studies in this thesis aim to determine physiological vital sign reference ranges for well newborns between 34+0/7 and 36+6/7 weeks of gestation. Objectives: The objectives of the studies in this thesis were to: systematically summarise the evidence in peer-reviewed literature on physiological vital sign reference ranges for well newborns greater than or equal to 34 weeks of gestation; to review contemporary neonatal and midwifery textbooks and publicly available grey literature (i.e. organisational websites, hospital policies and early warning tools) for vital sign reference ranges pertaining to well newborns of ≥ 34+0/7 weeks of gestation; to determine whether there are differences in vital signs in gestational age groups; and, if differences are identified, to establish physiological vital sign reference ranges for the well late preterm group and validate the reference ranges. Research Design: A systematic review of literature was initially undertaken followed by a scoping review of textbooks and grey literature to identify vital sign reference ranges for newborns ≥ 34+0/7 weeks of gestation. Quantitative research methods were used to meet the remaining study objectives. Study One was conducted as a single site prospective observational study of 30 newborns, comprised of three gestational age groups: late preterm (34+0/7 – 36+6/7), early term (37+0/7 – 38+6/7), and term (39+0/7 – 40+6/7). This involved continuously recording heart rate, respiratory rate, and peripheral oxygen saturation for up to six hours and periodic monitoring of temperature and blood pressure to determine whether physiological vital signs differed between the groups. The results of Study One informed the design of Study Two. This involved a shorter recording time of up to two hours and periodic monitoring of temperature and blood pressure on 120 well, late preterm newborns in a single site prospective observational study. The reference ranges established in Study Two underwent validation in Study Three, in which a cross-sectional design was used to validate the data with data from the medical records of a group of late preterm newborns. Results: The searches of literature resulted in primary studies (n = 10), textbooks (n = 7) and grey literature (n = 11). Inconsistencies in and a dearth of vital sign ranges for gestational age groups other than term were identified. Details of how reference ranges were calculated were only provided in the peer reviewed literature. Study One generated a combined total of 284,542 heart rate values, 275,826 respiratory rate values, 287,572 peripheral oxygen saturation values, and 60 temperature and 60 blood pressure data points for analysis. Heart rate was found to be significantly different, with late preterm heart rates on average 13.4 beats per minute (bpm) (95 % CI 6.5 – 20.4) higher than term newborns. Respiratory rate was on average -2.0 respirations per minute (rpm) (95 % CI -6.8 – 2.7) lower for late preterm newborns compared with term newborns. Peripheral oxygen saturation was on average -1.17 log units (95 % CI -2.32 – -0.01) lower for late preterm newborns compared with term newborns. There were statistically non-significant differences between gestational age groups for temperature (p = 0.38) and blood pressure (systolic p = 0.93, diastolic p = 0.54, mean arterial pressure p = 0.64).Study Two generated a total of 364,596 heart rate, 365,208 respiratory rate, 360,494 peripheral oxygen saturation, 240 temperature and 240 blood pressure data points for analysis to establish reference ranges for each physiological vital sign. Established reference ranges were: heart rate (bpm) 102-164; respiratory rate (rpm) 15 – 67; peripheral oxygen saturation (%) 85 – 100; temperature (°C) 36.4 – 37.6; systolic blood pressure (mmHg) 51 – 86; diastolic blood pressure (mmHg) 28 – 61; and mean arterial pressure (mmHg) 35 – 68.Study Three demonstrated the validation of some of the reference ranges using data from 20 measurands. It was not possible to validate blood pressure, as this vital sign is not routinely measured on well newborns in either the postnatal ward or special care nursery. Heart rate was not validated with either the initial measurands or the subsequent 20 measurands. Examination of the analytical procedures and biological characteristics of the measurands revealed a common factor of the occurrence of a maternal complication during pregnancy. When excluding these complications, the heart rate reference range was validated.Conclusions: Well late preterm newborns have a number of physiological vital sign differences compared to term newborns. Vital sign reference ranges were established for late preterm newborns with respiratory rate, temperature and peripheral oxygen saturation reference ranges validated. Heart rate was validated when excluding newborns born to mothers with pregnancy related complications. Blood pressure could not be validated as it is not routinely conducted on the postnatal ward.