The influence of repeated pain exposure on morning salivary cortisol in term and preterm neonates

Introduction
Introduction: Because neonates in the intensive care units (ICU) experience recurrent stress due to painful medical procedures, they are at risk of dysregulation of the hypothalamus-pituitary-adrenal (HPA) axis. Aim of the study: To evaluate the influence of repeated pain exposure on morning salivary cortisol (SC) in newborns admitted to the ICU.

Material and methods
The neonates were divided into 3 groups: term (370/7–416/7 weeks), moderate to late preterm (320/7–366/7 weeks), and very preterm (< 320/7 weeks). The hospital stay was prospectively monitored for the number of the most common medical procedures. At least 2 saliva samples for morning SC were collected after completion of 35 weeks of postmenstrual age (PMA) in preterm infants and before discharge in term neonates. The results of SC were compared with the reference intervals for healthy term newborns.

Results
The study group consisted of 57 patients: 21 term, 17 moderate to late preterm, and 19 very preterm neonates. Very preterm neonates obtained the highest values of mean morning SC in comparison to moderate to late preterm and term infants (3.83 [1.67–8.81] ng/ml vs. 2.44 [1.94–4.38] ng/ml vs. 2.15 [1.5–5.25] ng/ml, p = 0.45). The relationship between mean morning SC and the number of invasive blood samplings was found only in term newborns (Rs = –0.44, p < 0.05). 46% of all SC measurements in very preterm, 47% in moderate to late preterm, and 46% in term infants were within the reference intervals for healthy newborns.

Conclusions
High exposure to painful procedures seems to dampen the morning SC in term, but not in preterm infants.