While 24 newborn infants (ages, 2 to 48 hours; gestational ages, 24 to 42 weeks) breathed various concentrations of oxygen, the PO2 values on their unheated skin surface were measured by an unheated microcathode electrode for transcutaneous PO2 monitoring. In infants with arterial PO2 values in the range of 50 to 100 torr and with similar skin temperatures, the mean surface PO2 of unheated skin was inversely related to birth weight: 27.2 torr in infants weighing less than 1,500 gm, 14.3 torr in infants weighing 1,500 to 2,500 gm, and 2.9 torr in infants weighing more than 2,500 gm. In the smallest infants, the skin surface PO2 was significantly related to arterial P02: it was about one third of arterial PO2 as estimated by a second electrode for transcutaneous PO2 monitoring heated to 44°C. Phototherapy, crying, or blood transfusion increased the surface P02 of unheated skin, but not the tcPO2 measured at 44°C. These findings suggest that blood flow to the skin in excess of its metabolic needs due to immature control of cutaneous circulation, along with low resistance to oxygen diffusion, determines the high oxygen permeability of skin in premature infants.

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