Oxygen
CLN’S LAB 2006: SUPPORTING CLINICAL DECISIONS SERIES
Oxygen Saturation
A Guide to Laboratory Assessment
BY SHANNON HAYMOND, PHD uman life depends on the oxygen transport by hemoglobin. In healthy patients, the majority of molecular oxygen (O2) is bound to hemoglobin and only a small fraction is dissolved in blood. But in patients with respiratory problems or certain metabolic and genetic disorders, the fraction of oxygenated hemoglobin can fall to dangerously low values. Therefore, laboratory assessment of oxygen saturation (SO2)—the percentage of hemoglobin saturated with oxygen—provides an important indicator of a patient’s cardio-respiratory status and is frequently used in the emergency department, during general and regional anesthesia, and in intensive care settings. Although the measured parameters are quite different for each, the three major analytical methods for measuring oxygen saturation—arterial blood gas analyzers, pulse oximetry, and CO-oximetry—are frequently used interchangeably by health care workers. Arterial blood gas analyzers calculate estimated oxygen saturation (O2sat) in a blood sample based on empirical equations using pH and PO2 values, while pulse oximeters monitor arterial blood oxygen saturation, commonly referred to as SpO2 or SaO2, noninvasively by passing selected wavelengths of light through an area of the body, such as a finger. Both are measures of oxygen saturation.
The Clinical Laboratory Standards Institute (CLSI) defines O2sat as an estimated value based on a calculation, whereas SaO2 and SpO2 refer to the arterial saturation leading results, so health care professionals need to understand the differences between these methods and the limitations of each. This article will review the basics of oxygenmutations, such as the thalessemias, reduce the quantity of α- or ß-chain synthesis in the hemoglobin subunit or lower the solubility of hemoglobin—as occurs with HbS (sickle cell hemoglobin) or HbC (hemoglobin C), for
Oxygen Saturation
A Guide to Laboratory Assessment
BY SHANNON HAYMOND, PHD uman life depends on the oxygen transport by hemoglobin. In healthy patients, the majority of molecular oxygen (O2) is bound to hemoglobin and only a small fraction is dissolved in blood. But in patients with respiratory problems or certain metabolic and genetic disorders, the fraction of oxygenated hemoglobin can fall to dangerously low values. Therefore, laboratory assessment of oxygen saturation (SO2)—the percentage of hemoglobin saturated with oxygen—provides an important indicator of a patient’s cardio-respiratory status and is frequently used in the emergency department, during general and regional anesthesia, and in intensive care settings. Although the measured parameters are quite different for each, the three major analytical methods for measuring oxygen saturation—arterial blood gas analyzers, pulse oximetry, and CO-oximetry—are frequently used interchangeably by health care workers. Arterial blood gas analyzers calculate estimated oxygen saturation (O2sat) in a blood sample based on empirical equations using pH and PO2 values, while pulse oximeters monitor arterial blood oxygen saturation, commonly referred to as SpO2 or SaO2, noninvasively by passing selected wavelengths of light through an area of the body, such as a finger. Both are measures of oxygen saturation.
The Clinical Laboratory Standards Institute (CLSI) defines O2sat as an estimated value based on a calculation, whereas SaO2 and SpO2 refer to the arterial saturation leading results, so health care professionals need to understand the differences between these methods and the limitations of each. This article will review the basics of oxygenmutations, such as the thalessemias, reduce the quantity of α- or ß-chain synthesis in the hemoglobin subunit or lower the solubility of hemoglobin—as occurs with HbS (sickle cell hemoglobin) or HbC (hemoglobin C), for