Background: The femoral vein is an important site for central venous access in newborns and infants. The objectives of this study are to determine whether age or weight can be used clinically to predict the size of the femoral vein in newborns and infants, and to compare the size of the vein in each individual in both the supine and reverse Trendelenburg positions.

      Results:
      Analysis was done in 24 euvolemic individuals, each studied in
            both the supine and reverse Trendelenburg positions. Twelve of these
            individuals were newborns and 12 were infants. We used two-factor analysis of
            variance to explore differences between groups and multiple linear regression
            analysis to estimate the strength of the relationship between variables. In the
            infant group, there was a correlation between femoral vein diameter and weight.
            There was no correlation between weight and vessel size in newborns. In both
            the newborn and infant groups, vessel diameter increased with subjects in the
            reverse Trendelenburg position (P < 0.01).


      Conclusion:
      Weight is predictive of femoral vein diameter in infants, but not
            in newborns. In infants, weight might serve as a more sensitive index for
            estimating size of the femoral vein in order to determine accurately the size
            of intravascular catheter appropriate for cannulation. The diameter of the
            femoral vein increases in the reverse Trendelenburg position compared with that
            in the supine position in both newborns and infants. A large prospective study
            is required to validate these findings.