Objective: This study will examine maturation of vasomotor tone by measuring central and peripheral body temperature of 30 extremely low birth weight (ELBW) infants in relationship to peripheral perfusion during the first 5 days of life. We will examine the ability of each infant to exhibit peripheral vasoconstriction in response to decreased abdominal skin temperature and to keep abdominal temperature higher than peripheral using thermistor temperatures, peripheral perfusion index and infrared thermal imaging. The study will provide data on which to base a multi-center study to examine the relationship between the maturation of vasomotor tone and morbidity--intraventricular hemorrhage (IVH) and necrotizing enterocolitis (NEC)--in ELBW infants. Methods: Consent will be obtained from parents prior to infant birth. ELBW infants less than 29 weeks gestation and less than 1000 gram birth-weight will be enrolled at NICU admission. Physiologic variables will be sampled every minute for 120 hours. Abdominal and peripheral body temperature will be measured using thermistors and data loggers. Peripheral blood flow will be measured using peripheral perfusion index from a Masimo Radical-7 monitor. An infrared camera will be used to measure body surface temperature once daily, through the incubator hood adapted for thermal imaging. Infants will be video-recorded continuously over the 5-days to capture care that may expose the infant to cold environmental temperatures. Infant medical records will be reviewed until NICU discharge. Data Analysis: Data will be analyzed using SAS software, first as case studies within-subjects, then with comparison between subjects in three gestational age groups: 23-25, 25 1/7-27, and 27 1/7-28 6/7 weeks. The State Space approach to time series analysis and logistic regression will be used to determine time of vasomotor tone maturity within each infant and average over each infant group. Time of vasomotor maturity will be determined as the age at which each infant has the ability to decrease peripheral temperature 0.5-2? C below abdominal temperature in response to a decrease in abdominal temperature below 37?C and when the infant can consistently keep abdominal temperature greater than peripheral temperature. Clinical care events will be analyzed in relationship to decreases in body temperature and subsequent recovery to baseline temperature. Events causing decreased internal body temperatures may include suctioning, ventilation with an oxygen bag or infusion of fluids into umbilical catheters. Events causing decreases in external environmental temperature are related to opening the incubator portholes or doors. All events will be coded from video data and entered into analyses with physiological variables. Cross correlations will be used to compare peripheral temperature, peripheral perfusion and internal incubator temperature. Infrared thermal measurements will be compared to body temperature measured by thermistor to evaluate the use of thermal imaging for overall body temperature and perfusion. Occurrence of IVH and NEC will be related to each infant's gestational and postnatal age of vasomotor tone maturity.
Extremely premature infants are subject to low temperatures during their first few days of life. These infants have an increased risk for brain injury during this time that may be due to immature regulation of blood flow, increasing their neurosensory, developmental and physical risks. This study will provide evidence of the time when the ability to control blood flow to the feet and back to the brain and heart becomes mature in extremely premature infants during their first week of life, allowing interventions to be developed to decrease these developmental risks.
