Relations between behavioral and cardiac autonomic reactivity to acute pain in preterm neonates

Abstract

Objective: The purpose of this study was to assess relations and concordance between behavioral and physiologic reactivity to pain in preterm neonates at 32 weeks postconceptional age as a function of gestational age at birth.

Setting: Level III neonatal intensive care unit.

Design/patients: The study group comprised 136 preterm neonates (mean [range] birthweight, 1,020 g [445-1,500 g]: gestational age at birth, 28 weeks [23-32 weeks]) separated into three groups according to gestational age at birth as follows: 23 to 26 weeks (n = 48), 27 to 29 weeks (n = 52), and 30 to 32 weeks (n = 36).

Outcome measures: Reactivity to routine blood collection at 32 weeks postconceptional age was assessed using bedside-recorded behavioral and autonomic measures. Coders who were blinded to the study design scored behavioral responses (facial activity using the Neonatal Facial Coding System, sleep/waking state, and finger splay). Autonomic reactivity was assessed by change in heart rate and spectral analysis of heart rate variability (change in low-frequency and high-frequency power, and the ratio of low-frequency to high-frequency power during blood collection).

Results: Facial activity and state correlated moderately with change in heart rate across gestational age groups (r = 0.41-0.62). Facial activity and state did not correlate significantly with change in low-frequency and high-frequency power, or the ratio of low-frequency to high-frequency power (r = 0.00-0.31). Finger splay did not correlate with any autonomic recording (r = 0.03-0.41). Concordance between established biobehavioral measures of pain revealed individual differences. Although some neonates showed high behavioral but low physiologic reactivity, other neonates displayed the opposite reaction; however, the majority displayed concordant reactions.

Conclusions: The study findings confirm the value of measuring domains independently, especially in neonates born at a very young gestational age.

FIG. 1

Associations between behavioral and autonomic reactivity at 32 weeks postconceptional age. Symbols greater than r = 0.4 are significant at p <0.01. NFCS, Neonatal Facial Coding System at squeeze; state, state at squeeze; HR, change in heart rate from baseline to squeeze; LFP, change in low-frequency power from baseline to squeeze; HFP, change in high-frequency power from baseline to squeeze; LFP/HFP, ratio of LFP to HFP at squeeze.

FIG. 2

Associations between finger splay and autonomic reactivity at 32 weeks postconceptional age. Symbols greater than r = 0.25 are significant at p <0.01. Splay, finger splay at squeeze; HR, change in heart rate from baseline to squeeze; LFP, change in low-frequency power from baseline to squeeze; HFP, change in high-frequency power from baseline to squeeze; LFP/HFP, ratio of LFP to HFP at squeeze.

FIG. 3

Associations among behavioral reactivity measures at 32 weeks postconceptional age. Symbols greater than r = 0.25 are significant at p ≤ 0.05. NFCS, Neonatal Facial Coding System; state, state at squeeze; splay, finger splay at squeeze.

FIG. 4

Associations among autonomic reactivity measures at 32 weeks postconceptional age. Symbols at r = 0.3 or greater are significant at p <0.05. HR, change in heart rate from baseline to squeeze; LFP, change in low-frequency power from baseline to squeeze; HFP, change in high-frequency power from baseline to squeeze; LFP/HFP, ratio of LFP to HFP at squeeze.