The pain of heel prick and its measurement in preterm infants.

Variability of physiological parameters was used as a measure of stress in the newborn infant. There was a significant increase in variability of the heart rate (P < 0.01) when the stab of the heel prick occurred in addition to the other elements of the procedure (positioning, warming, alcohol swab cleansing and squeezing). This dummy procedure itself caused some increase in variability although this was not significant at the 5% level. There were similar significant increases in variability of the respiratory rate and O2 and CO2 tensions in the blood (P < 0.05) during the stab procedure.