Although traditional pulse oximetry is a standard monitor in anesthesia, it is limited in its ability to detect tissue hypoxia. Typical interventions used to increase SpO2 may not necessarily improve tissue oxygenation, particularly in ischemic organs. Regional oximeters measure a mix of arterial, capillary, and venous blood in brain or peripheral tissues. A new regional oximeter (O3™, Masimo, Irvine, CA) will become available in the United States soon, pending Food and Drug Administration approval.
Dr. Daniel T. Redford, Department of Anesthesiology, University of Arizona Medical Center, Tucson, Arizona, Dr. Samata Paidy, Department of Anesthesiology, University of Arizona Medical Center, Tucson, Arizona, and Dr. Faisal Kashif, Masimo Corporation, Irvine, California, tested the monitor in 23 volunteers (27 originally, though 4 dropped due to exclusion criteria) who breathed oxygen in different concentrations to achieve arterial oxygen saturation plateaus between 100% and 70%. Their results are published in this month’s issue of Anesthesia and Analgesia and discussed in the article titled “Absolute and Trend Accuracy of a New Regional Oximeter in Healthy Volunteers During Controlled Hypoxia.”
The authors compared regional oximeter results obtained from the left side of the subject’s forehead to blood samples taken from the radial artery and internal jugular bulb vein. The authors calculated the expected cerebral oxygen saturation from the formula 0.3 x arterial oxygen saturation + 0.7 x jugular bulb oxygen saturation, “based on the arterial and venous components of the cerebral blood volume.” They compared 202 paired oxygen saturations measured plethysmographically with the saturation calculated from arterial and venous bulb saturation. The correlation coefficient was 0.87. The Masimo O3 provided a 4% root-mean-squared error for absolute accuracy and captured a relative root-mean-squared error of 2.1% for trend accuracy.
Monitoring continuous pulse oximetry became part of standard anesthesia monitoring in the 1980s. Its widespread use revolutionized patient safety. Developing technology to better and more accurately appreciate end organ oxygenation has the potential to do the same.