What is the difference between spo2 and sao2

When it comes to measurement of SpO 2 , transmissive pulse oxymetry is the commonest method in which a device passes two wavelengths of light to a photodetector through a body part, usually fingertip or earlobe in adults.

Here, red nm and infrared nm are the two wavelengths. Generally, o xygenated hemoglobin absorbs more infrared light and allows more red light to pass through. In contrast, deoxygenated hemoglobin allows more infrared light to pass through and absorbs more red light.

Ultimately, the ratio of the transmitted red light measurement to the infrared light measurement gives the SpO 2 value. The following formula helps to calculate the SpO2 value.

Moreover, the SpO 2 value serves as an unreliable surrogate marker for SaO 2 in critically ill patients. H owever, the validity of the relationship between SpO 2 and SaO 2 is dependent on a number of factors, including the adequacy of peripheral perfusion.

Also, besides its non-invasive nature, pulse oximetry provides attempts to the continuous measurement of oxygen saturation, which is useful in several clinical situations. These include surgery and post-anesthetic care units, neonatal care and NICU, emergency care, noninvasive transcutaneous pacing, etc.

Moreover, a significant feature of SpO 2 measurement is that it only measures the oxygen saturation of the functional hemoglobin, which is more accurate. Here, the functional hemoglobin refers to the hemoglobin capable of carrying oxygen.

On the other hand, non-functional hemoglobins include carboxyhemoglobin HbCO and methemoglobin METHb , which are incapable of carrying oxygen. Thus, the formula for the ideal blood saturation measurement is:.

SaO 2 refers to the measurement of oxygen saturation in arterial blood, but SpO 2 refers to the oxygen saturation in the arterial blood as measured by a pulse oximeter.

Notes The authors thank M. References 1. Pulse oximetry: fundamentals and technology update. Medical Devices ; 7 : —9. Do changes in pulse oximeter oxygen saturation predict equivalent changes in arterial oxygen saturation? Critical Care ; 7 : R Comparative evaluation of accuracy of pulse oximeters and factors affecting their performance in a tertiary intensive care unit. Pulse oximetry: understanding its basic principles facilitates appreciation of its limitations.

Respiratory Medicine ; : — Increased blood glycohemoglobin A1c levels lead to overestimation of arterial oxygen saturation by pulse oximetry in patients with type 2 diabetes. Cardiovascular Diabetology ; 11 : Hemoglobin lansing: a novel hemoglobin variant causing falsely decreased oxygen saturation by pulse oximetry.

American Journal of Hematology ; 84 : Available here. Samanthi Udayangani holds a B. Degree in Plant Science, M. Your email address will not be published. Figure Co-Oximeter.

Figure SPO2. Leave a Reply Cancel reply Your email address will not be published. SAO2 is the direct measurement of O2 bound to heme protein of haemoglobin in the blood. SPO2 measurement is the oximetric pulse measurement of functional saturation of haemoglobin with O2. Saturation Level in a Healthy Individual.

Device Used for Measurement. Invasiveness of the Technique Used.