PaO2, SaO2 and what constitutes adequate oxygenation in the premature newborn

3 neonates admitted into our intensive care unit had their arterial blood gases analyzed. A total of 64, 67 and 73 arterial blood samples were analyzed for the 3 neonates respectively. The relationship between PaO2 and the corresponding SaO2 were plotted in an oxygen hemoglobin dissociation curve. PaO2 of 50mmHg corresponded to SaO2 of 80%, 84% and 92% for the 3 babies respectively, reflecting the fact that SaO2 can differ considerably. PaO2 of 50mmHg or SaO2 of 87% by themselves are inadequate as indicators of lower limit of arterial oxygenation. Indeed a consideration of other factors such as oxygen consumption, cardiac output, hemoglobin concentration are integral to this issue. PaO2 of 70mmHg corresponded to SaO2 of 92%, 93% and 97% respectively. However, at the upper limit of arterial oxygenation, the oxygen hemoglobin dissociation curve flattens out and PaO2 is a more sensitive indicator of the upper limit of arterial oxygenation as compared to SaO2.