Measures of Stress Exposure for Hospitalized Preterm Infants

Background Extended hospitalization in neonatal intensive care units subjects preterm infants to multiple stress exposures that affect long-term cognitive functioning, motor development, and stress reactivity. Measurement of stress exposure is challenging with multiple measures of stress exposure in use, including counts of skin-breaking or invasive procedures or counts of noxious sensory exposures. Objectives The purpose of this analysis was to compare measures of stress exposure commonly used by researchers and to determine the predictive validity of these measures for early neurobehavior. We accomplished this objective through the following specific aims: (a) describe the stress exposures of preterm infants in the first 2 weeks of life, (b) determine the correlations among measures of stress exposure, and (c) compare the predictive validity of measures of stress exposure for early neurobehavior. Methods Very preterm infants born between 28 and 31 weeks postmenstrual age were enrolled from four neonatal intensive care units in a large Midwest city. We measured stress exposure over the first 14 days of life for each infant as a count of skin-breaking procedures, a count of invasive procedures, and cumulative scores derived from the Neonatal Infant Stressor Scale. Neurobehavior was assessed at 35 weeks postmenstrual age using the motor development and vigor and alertness/orientation subscales from the Neurobehavioral Assessment of the Preterm Infant. We used Spearman's rho to determine correlations among the measures of stress exposure and multiple linear regression to determine the predictive validity of each stress exposure measure for neurobehavioral outcomes. Results Seventy-one preterm infants were included in the analysis. We found marked variance across individuals in all measures of stress exposure. There were moderate-high correlations among the measures of stress exposure. No measure of stress exposure was associated with early neurobehavior. Discussion The stress experiences of hospitalized preterm infants vary. This variance is reflected in all measures of stress exposure. Because measures of stress exposure are highly correlated, the most objective measure requiring the least interpretation should be used. However, the currently available measures of stress exposure used in this analysis may not reflect the infant's physiological stress responses and fail to associate with early neurobehavior.