Fetal pulse oximetry: influence of tissue blood content and hemoglobin concentration in a new in-vitro model

To assess the influence of the blood content of the tissue and the hemoglobin content of the blood upon pulse oximetry at oxygen saturation ranges that commonly occur in the fetus during birth.

A new in-vitro model, which differs conceptually from models used by other authors, was developed to simulate the tissue. Our sensor measured absorption changes in red (640 nm) and infrared (880 nm) light as the blood concentration in the optical chamber changed in analogy to arterial pulsations.

Blood content of the tissue and hemoglobin content of the blood both affect the pulse oximetric measurement adversely, especially at low oxygen saturations. Our simulations indicate, for example, that at a true oxygen saturation (SaO2) of 30%, a blood content change from 10 to 6 vol% would cause an underestimation of SaO2 by more than 16% points.

Pulse oximetry at low saturations should take the blood content of the tissue and hemoglobin content of the blood into account in order to provide more accurate results.