Aim: To investigate the responses to painful and tactile stimulation in preterm and term infants in terms of changes in the plantar skin conductance activity (SCA) and behavioural state. Plantar SCA reflects activity in the sympathetic nervous system.
Design: The plantar SCA and behavioural state in response to nociceptive (the heel prick for blood samples, or immunization) and tactile (routine nursery handling) simulation was recorded in four different groups of infants (n=71): Preterm and term neonatal infants (defined here as up to 1 week old), and preterm and term infants in the postneonatal period.
Results: The preterm infants had significant increases in all skin conductance variables during both tactile and nociceptive stimulation (p<0.02), except for wave amplitude when newborns were heel pricked. The term infants displayed a more varied picture, but both the number and amplitude of the waves increased significantly during both procedures in the newborn groups, while the postneonatal groups only showed significant increases in wave amplitude during nociceptive stimulation (p<0.05). Tactile stimulation of the preterm newborn infants produced significantly higher increases in SCA than nociceptive stimulation (p<0.01), while the behavioural state was highest during nociceptive stimulation (p<0.05). A gradual change in this relation was seen with advancing total age.
Conclusion: Non-painful sensory stimulation of infants, especially the newborn and preterm ones, can produce equal or higher levels of physiological stress activation than painful stimulation. Repeated nociceptive stimulation probably sensitises the infants to pain.