Noninvasive Cellular Oxygenation Measurement During Graded Hypoxia Using Visible-Near-Infrared Spectroscopy

In critically ill patients, direct knowledge of intracellular pO₂ would allow for identification of cellular hypoxia, which when prolonged leads to organ failure. We have developed a visible-near-infrared optical system that noninvasively measures myoglobin saturation, which is directly related to intracellular pO₂, from the surface of the skin. We used an animal model of graded hypoxia from low levels of inspired oxygen (n = 5) and verified that low intracellular pO₂ is correlated with high steady-state serum lactate values. In addition, the pO₂ gradient between arterial blood and inside muscle cells was 83 mm Hg at 21% O₂, but fell to 24 mm Hg at 8% O₂. Continuous myoglobin saturation measurement in skeletal muscle displayed the same trends as cerebral oxygenation with no lag in changes over time, demonstrating its relevance as a measure of systemic oxygenation.