Skin microcirculation in neonatal polycythaemia and effects of haemodilution. Interaction between haematocrit,...

The cutaneous microcirculation was investigated before and 2-4 h after haemodilution in 13 newborn infants with polycythaemia. Skin microvascular perfusion was related to the haematocrit and to the presence of rhythmical changes in blood flow, reflecting vasomotor activity. The microcirculation was studied with a laser Doppler fluxmeter in a superficial microvascular bed represented by the dorsal hand skin. In five subjects, it was possible to combine laser Doppler flux measurements with microscopic quantitations of blood cell velocity in single, nailfold capillaries. In neonates less than 12 h postnatal age (n = 6), microvascular perfusion was only one-third that of the equally polycythaemic, but older infants (n = 7, p < 0.01). The higher perfusion in the older neonates with polycythaemia was associated with rhythmical variations in blood flow (3-5 cycles/min). There was no difference in skin temperature, blood pressure or heart rate between the two age groups. After haemodilution, the younger infants had developed rhythmical blood flow variations with the same characteristics as in the older group, in which the flow pattern was unchanged. In association, the laser Doppler flux had increased 304% in the younger and 73% in the older group (median values, p < 0.05 versus pretreatment values). The post-treatment change in laser Doppler flux corresponded to an increase in nailfold capillary blood cell velocity from 0.08 (0.02-0.23) mm/s prior to haemodilution to 0.21 (0.07-0.32) mm/s after treatment (n = 5, p < 0.05). Skin microcirculatory effects of neonatal polycythaemia and haemodilution vary in relation to vasomotor activity.