Biobehavioral Responses to Caregiving in Very Low Birth Weight Preterm Infants

Open Access
Haidet, Kim Kopenhaver
Graduate Program:
Biobehavioral Health
Doctor of Philosophy
Document Type:
Date of Defense:
April 04, 2005
Committee Members:
  • Elizabeth Susman, Committee Chair
  • Sheila Grace West, Committee Member
  • Douglas A Granger, Committee Member
  • Keith Howard Marks, Committee Member
  • stress
  • preterm infants
  • psychobiology
Life-sustaining medical care in the neonatal intensive care unit (NICU) may cause discomfort and stress in very low birth weight (VLBW) preterm infants. Moreover, repeated exposures to unmitigated stress may contribute to illness and poor developmental outcomes. This study examined linkages between biological and behavioral responses to caregiving as predictors of health outcomes in preterm infants. The specific aims of the study were: (a) to examine hypothesized relationships between neuroendocrine responses, vagal tone, and behavioral responses within the context of nursing caregiving in the NICU, (b) to test whether early patterns of hormonal, heart rate, and behavioral responses in the first few days of life are predictors of health outcomes for very low birth weight infants at the time of discharge, and (c) to identify maternal perceptions of the NICU environment and the effects of these perceptions on maternal-infant interaction and subsequent parenting beliefs. The hypotheses were: 1 (a) there will be direct positive relationships between cortisol reactivity and autonomic parameters, (b) there will be direct positive relationships between cortisol reactivity and behavioral responses, (c) there will be direct positive relationships between heart rate variability (HRV) and behavioral responses, 2 (a) infants with higher cortisol responses to handling will have poorer health outcomes than infants with lower cortisol reactivity, (b) infants with lower HRV at rest will have poorer health outcomes than infants with higher heart rate variability, 3 (a) infants with higher behavioral distress will have poorer health outcomes than infants with lower distress, (b) infants with higher cortisol levels post-handling (at 60 minutes) will have poorer health outcomes than infants with lower cortisol levels post-handling, 4 (a) mothers reporting higher stress will be less responsive to their infants than mothers with lower stress, and (b) mothers who are less responsive to their infants will rate themselves lower in parenting competency than mothers with high responsiveness. Thirteen preterm infants were enrolled in this prospective, observational study, with each infant serving as her/his own control. On day 4 - 5 of life, morning plasma samples were obtained for assessment of cortisol levels from an existing umbilical catheter while simultaneously measuring heart and respiratory rates, and oxygen saturations at baseline and 30 and 60 minutes post-handling during standard nursing care. Activity, state, and behavioral stress signals were quantified using the NIDCAPÒ observational method. Resting HRV was measured on day five and one month postnatally. Health outcomes data were collected via chart audit. Maternal questionnaires and behavioral interaction ratings were administered during the first week of hospitalization and one month postnatally. The results of the analyses showed that cortisol reactivity was highly positively associated with visceral cues (p = 0.03) during handling and tachypnea (p = 0.04) post-handling. HRV was highly positively correlated with motor, facial, and attentional cues. Recovery (60 min) cortisol was highly positively associated with duration of ventilation (p = 0.03), duration of oxygen (p = 0.02), and length of stay (p = 0.005). Those infants with greater high frequency HRV (vagal tone) achieved oral feeding earlier (p = 0.048) and had improved health outcomes including: shorter ventilation (p = 0.03), lower incidence of retinopathy (p = 0.03), and shorter length of stay (p = 0.04). Infants demonstrating expression of facial distress cues (brow bulge, eye squeeze) had a higher incidence of nosocomial sepsis (p = 0.04), longer duration of oxygen therapy (p = 0.02), and longer length of stay identified by correlation and regression analyses (p = 0.02). Mothers of study infants reported high general stress levels during early hospitalization; however, maternal stress levels did not predict nurse-rated competency of mothers at one month of age. Mothers rated by NICU nurses as more competent and sensitive to their infants had higher self-ratings of competency in parenting at one month of age. All infants exhibited hormonal and behavioral reactivity to handling. The majority quieted and had lower cortisol levels at one hour post-handling in response to appropriate pacing of care and containment. Those infants with persistent tachypnea and higher cortisol levels post-handling had higher respiratory morbidity. Behavioral distress responses (facial and visceral cues) were associated with higher rates of nosocomial sepsis and longer oxygen duration; these indicators represented a uniquely vulnerable subgroup, more challenged by environmental stimulation. In contrast, more robust infants demonstrating high motor and attentional behaviors had greater high frequency HRV and improved outcomes. This study adds to the accruing evidence that vagal tone represents an important homeostatic mechanism that may be an independent measure of stress vulnerability. In addition, cue-based caregiving was crucial in promoting infant stability. Further investigation with a larger sample of newborns is required to confirm the clinical significance of these findings.