Last updated: 05/30/2013
Oxygen travels in the blood as a soluble gas or bound to hemoglobin. This is most clearly demonstrated with the equation for O2 content:
(1.34 x Hgb x SaO2) + (Pa02 x 0.003)
The P-50 of oxygen is the oxygen tension at which 50% of the hemoglobin is bound to O2. The P-50 of adults at a temperature of 37 degrees and a pH of 7.4 is 27 mmHg. In the newborn, fetal hemoglobin (HgbF) has extremely high oxygen affinity and the P50 is low (18-19 mmHg,) because 2,3-DPG is low and fetal hemoglobin (HbF) reacts poorly with 2,3-DPG. After birth, total hemoglobin, including HgbF decreases rapidly reaching a nadir at 2-3 months. At the same time, the P-50 rises, exceeding the normal adult value by 4-6 months (30 mm Hg) and reaching the highest at 10 months, and remaining high until the first decade. Children therefore have a lower 02 affinity for hemoglobin than adults and higher rate of O2 unloading. This translates to more efficient 02 unloading with lower levels of hemoglobin in infants and children.
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.