Pain Variability in Preterm Infants

Abstract

Background: Infants born preterm are exposed to repeated medically necessary painful procedures during their neonatal intensive care unit (NICU) admission. Particularly in preterm infants, trajectories of pain reactivity and regulation are not well understood. Objectives: (1) classify individual pain response trajectories over two-minutes following medically indicated heel lances in preterm infants during their NICU admission; (2) compare mean pain scores within each trajectory class to the sample mean; (3) investigate the stability of classes over time within infants; and (4) explore whether pain treatment, sex, gestational age at birth, previous pain exposure, and postnatal age at time of procedure are associated with pain trajectory class. Methods: This study used existing data collected by the Trial of Repeated Analgesia with Kangaroo Mother Care (TRAKC) study. TRAKC was a single-blind, three-arm, parallel group randomized clinical trial examining the efficacy of kangaroo care and sucrose alone and in combination as methods of infant pain control during repeated procedures in the NICU. Pain was measured using the Premature Infant Pain Profile at 30, 60, 90, and 120 seconds following the heel lance. Group based trajectory modeling was used to classify pain response in this two-minute time period. Results: 236 infants contributed 610 painful procedures. Median gestational age at birth was 33 weeks. A model with five pain trajectory classes best fit the data. Three of the trajectories were stable over time at different levels of intensity from low-mild to low-moderate pain. One trajectory reflected a linear reduction from high- to low-moderate pain. The final trajectory showed variable pain at moderate-high levels. At all procedures and at all times points, three classes were at least one-point different from the overall sample mean pain score. Overall, 89 (38%) infants were assigned a different class for each available procedure, 126 (53%) maintained the same class for two procedures, and 21 (9%) maintained the same class for all three procedures. No examined infant or treatment characteristic was found to be meaningfully different in a given class. Conclusions: In this sample of preterm infants receiving pain relieving interventions, most pain response trajectories reflected mild to low-moderate pain that was stable in the two-minutes post heel lance initiation. Pain trajectories were not consistent over multiple procedures within infants, and an overall mean pain score for the sample may misrepresent subgroups of higher and lower pain.