Capillary-venous hematocrit differences in newborn infants. I. Relationship to blood volume, peripheral blood flow, and acid base parameters.

Venous and capillary hematocrit, acid base values, and circulatory parameters were measured simultaneously in 92 newborn infants within six hours of birth. Gestational age ranged from 26 to 41 weeks. The capillary/venous hematocrit ratio (Hctc/Hctv) was greater than 1.00 in 89 infants. We found significant inverse correlations between Hctc/Hctv and several parameters, such as pH (r = -0.82), standard bicarbonate (r = -0.73), systolic blood pressure (r = -0.51), and peripheral blood flow (r = -0.70). Most of the infants with a Hctc/Hctv of 1.20 and above had red cell mass values of less than 35 ml/kg. However, blood volume apparently did not influence the Hctc/Hctv. Gestational age appeared to affect Hctc/Hctv only before 30 weeks, when compared with the Hctc/Hctv of term infants. Our results indicate that disturbed circulation, and in particular, disturbed microcirculation is involved in the development of high Hctc/Hctv ratios. We strongly advise that hematocrits obtained by skin prick from a sick newborn infant should not be relied on as they may give misleading information on oxygen carrying capacity to vital organs.