Aim: Despite being widely recognized, the cephalocaudal progression of jaundice in newborns (Kramer's Rule) has never been satisfactorily explained. The aim of this study was to test the hypothesis that the cephalocaudal progression of jaundice in newborns is related to regional differences in skin temperature and skin perfusion.
Methods: A convenience sample of 50 infants was included in the study. On each infant, a transcutaneous bilirubin, skin temperature and capillary refill time measurement was made at five sites; the forehead, sternum, lower abdomen, mid thigh and sole. The relationship between the three variables was studied by analysis of variance.
Results: The transcutaneous bilirubin measurements upheld Kramer's observation, being significantly higher at the head and chest than at the thigh and sole (P < 0.001). A similar pattern was found for both skin temperature and capillary refill, both significantly different at the head compared to the sole (P < 0.001).
Conclusion: The results of the study support the hypothesis that the cephalocaudal progression of jaundice in newborns is a consequence of diminished capillary blood flow in distal parts of the body. It is hypothesized that newborn infants preferentially perfuse their head and proximal parts of their body in the first few days of life, leading to higher temperatures and increased bilirubin deposition at these sites.