Prematurity and neonatal noxious events exert lasting effects on infant pain behaviour.

BACKGROUND

There is concern that exposure of preterm infants to noxious insults over a prolonged period may have long term effects on their developing nervous system.

AIMS

To investigate medium and long term effects of heel pricks in infants over the first year of life.

STUDY DESIGN

Study 1-a longitudinal study, 2 days and 4 weeks after heel prick. Study 2-a cross sectional study over the first year of life.

SUBJECTS

Study 1-13 healthy preterm (PT) infants. Study 2-63 full term (FT) and 62 PT infants, divided into 3 timed groups (0-20, 21-37 and 38-52 weeks postterm and corrected for prematurity).

OUTCOME MEASURES

Threshold responses (flexion withdrawal (FWR) , gross body movements (GBM) and grimace (G)) to increasing mechanical force applied with Von Frey filaments.

RESULTS

Study 1-Thresholds were all significantly lower (more sensitive) from the pricked heel compared to the contralateral side at 2 days and 4 weeks. Study 2-There were significant differences in threshold between PT and FT infants at all time points for both FWR (P=0.001, <0.001, <0.001) and GBM (P=<0.001, <0.001, 0.009 respectively), the preterm infants always being lower. The threshold for the FWR in FT infants steadily increased, but the threshold for the PT infants remained the same. GBM thresholds increased during the year in both FT and PT infants, but were always significantly lower in the ex-preterm group (P<0.012).

CONCLUSIONS

Either PT birth or repetitive procedures associated with such birth alters the sensitivity threshold of PT infants compared with FT infants for at least the first year of life.