Summary Response:
The accuracy of StO2 should not be affected by the presence of hemoglobin-based blood substitutes. HTI has tested one investigational blood substitute using an in vitro blood-loop circuit and found no effect on StO2’s accuracy.1 Note: no blood substitutes are currently approved for human use in the U.S.
A potential interference with StO2 could arise if a blood substitute circulates in the body for a prolonged time and its hemoglobin content is oxidized to methemoglobin.
Methemoglobin, a non oxygen-carrying variant of normal hemoglobin, is ordinarily present only at low levels in the body and is known to affect StO2 measurements.2 Elevated methemoglobin can cause StO2 levels to be reported artifactually high.
The extent to which this would be a problem with a blood substitute in practice is unknown due to the absence of any such agent approved for human use.
Evidence to support response:
1Myers D unpublished data Hutchinson Technology 2004.
2Myers DE, Anderson LD, Seifert RP, Ortner JP, Cooper CE, Beilman GJ, Mowlem JD. Noninvasive method for measuring local hemoglobin oxygen saturation in tissue using wide gap second derivative near-infrared spectroscopy. J Biomed Optics. 2005;10(3)034017:1-18.