Heart rate dynamics during acute pain in newborns.

Autonomic nervous system modulation of heart rate is significantly altered during painful procedures in newborns. Most studies investigating pain employed only linear-based analysis methods, thus ignoring the complex, non-linear nature of heart rate control mechanisms. The emergences of dynamic, nonlinear analysis methods enable us to uncover information embedded in the fluctuations of heart rate not otherwise noticeable. Our objective was to examine how cardiac dynamics change in newborns who undergo heel lancing by analyzing linear and nonlinear characteristics of heart rate fluctuations. We used dynamic nonlinear analyses methods to reveal heart rate variability and complexity alterations during painful stimulus in newborns. Poincaré plots were applied to examine the dynamics of the system, sample entropy to investigate the complexity of the system, and detrended fluctuation analysis, to reveal the fractal properties of the system. Heart rate significantly increased (165 vs.123 beats per minute, p < 0.001) while variability decreased. Sample entropy and the quantitative measures of the Poincaré plots (SD1 and SD2) significantly decreased during heel lancing (0.75 vs. 1.0, p < 0.01; 6.4 vs. 12.8, p < 0.001; and 30.4 vs. 50.5, p < 0.01, respectively). Detrended fluctuation analysis showed a significant decrease in the short-term scaling exponent α1 (1.06 vs. 1.3, p < 0.001), and an increase in the long-term scaling exponent α2 (1.5 vs. 1.1, p < 0.001). Our results indicate altered complexity of heart rate variability during painful stimulus in newborns and disruption of the mechanisms that regularly control it. Such alterations resemble certain pathological conditions and may represent stress reaction.

Heel-lancing in newborns: behavioral and spectral analysis assessment of pain control methods.

OBJECTIVE: Pain experience can alter clinical outcome, brain development, and subsequent behavior in newborns, primarily in preterm infants. The aims of this study were (1) to evaluate several simple, commonly used methods for pain control in newborns and (2) to evaluate the concordance between behavioral and autonomic cardiac reactivity to pain in term neonates during heel-lancing. METHODS: A prospective study was conducted of 180 term newborn infants who were undergoing heel-lancing for routine neonatal screening of phenylketonuria and hypothyroidism. Newborns were assigned to 6 groups: (1) control (no pain relief intervention); (2) nonnutritive sucking; (3) holding by mother; (4) oral glucose solution; (5) oral formula feeding; or (6) breastfeeding. Outcome measures included the Neonatal Facial Coding System score; cry duration; and autonomic variables obtained from spectral analysis of heart rate variability before, during, and after heel-lancing. RESULTS: Infants with no pain control showed the highest pain manifestation compared with newborns to whom pain control was provided. Infants who breastfed or received an oral formula showed the lowest increase in heart rate (21 and 23 beats per minute, respectively, vs 36; P < .01), lowest neonatal facial score (2.3 and 2.9, respectively, vs 7.1; P < .001), lowest cry duration (5 and 13 seconds, respectively, vs 49; P < .001), and lowest decrease in parasympathetic tone (-2 and -2.4, respectively, vs 1.2; P < .02) compared with the other groups. CONCLUSIONS: Any method of pain control is better than none. Feeding and breastfeeding during heel-lancing were found to be the most effective methods of pain relief.