Developmental changes in infant pain expression during immunization injections.

Developmental changes in pain expression provoked by routine immunization injections during the first 2 years of life were examined. An interval-sampling, behavioral observation system was developed to code categories of expressive behavior in infants, their mothers and the nurse responsible for the injection. Qualitative changes were observed in the infants' behavior, with those less than 12 months of age responding in a more spontaneous, diffuse manner, whereas the older infants displayed more anticipatory distress, descriptive language and goal-directed movement. Mothers and the nurse actively interacted with each other and the infant with a range of vocal and nonvocal actions. The findings justified the use of unobtrusive, naturalistic observation as a means of assisting practitioners who suffer from an inadequate knowledge-base on pain in children.