The key difference between SAO2 and SPO2 is in the type of measurement of O2 levels in the blood. SAO2 or Saturation of Oxygen is the direct measurement of O2 bound to heme protein of hemoglobin in the blood. SPO2 measurement or oximetric measurement of O2 bound to hemoglobin is an indirect measurement of saturation of haemoglobin with O2.
SAO2 and SPO2 are measured during different disease conditions to monitor the level of available O2 in hemoglobin. The saturation levels of O2 bound to hemoglobin will provide details regarding the efficiency of the alveolar lung system.
CONTENTS
1. Overview and Key Difference
2. What is SAO2
3. What is SPO2
4. Similarities Between SAO2 and SPO2
5. Side by Side Comparison – SAO2 vs SPO2 in Tabular Form
6. Summary
What is SAO2?
Saturation of O2 (SAO2) in blood defines the percentage of hemoglobin binding sites that occupied with O2. Each hemoglobin molecule can occupy four O2 molecules as it can allosterically modify its conformation to facilitate binding of O2 to its binding site. The normal SAO2 value of a healthy individual occurs between 95 – 100 %. However, this may increase during conditions such as polycythemia and hyper ventilation. SAO2 decreases during anemia, hypoventilation, and bronchospasm.
Figure 01: Co-Oximeter
The co-oximeter measures SAO2. The ratio between oxyhemoglobin to all other types of hemoglobin provides the SAO2 value. Other types of hemoglobin include deoxyhemoglobin, methaemoglobin, carboxyhemoglobin, sulfhemoglobin and carboxy sulfhemoglobin.
What is SPO2?
SPO2 or the oxygen saturation measurement by pulse oximetry measures the functional saturation of hemoglobin. SPO2 is the ratio between the amount of oxygenated hemoglobin to the sum of deoxyhemoglobin and oxyhemoglobin. Thus, the SPO2 value will not be the same as the SAO2 value.
This method of obtaining the saturation of O2 in hemoglobin is more efficient and rapid in comparison with the co-oximeter measurement.
Figure 02: SPO2
The SPO2 levels in a healthy individual should be more than 94%. The levels can increase or decrease for different health conditions as in SAO2.
What are the Similarities Between SAO2 and SPO2?
- Both SAO2 and SPO2 depend on the concentration of O2 in blood.
- SAO2 and SPO2 measure the saturation of O2 in haemoglobin.
- Both the levels of SAO2 and SPO2 increase during hyper ventilation.
- The SAO2 and SPO2 levels decrease during hypo ventilation and anaemic.
What is the Difference Between SAO2 and SPO2?
SAO2 vs SPO2 |
|
| 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 | |
| SAO2 in healthy person should be 95 – 100%. | SPO2 in healthy person should be more than 94%. |
| Device Used for Measurement | |
| Co-oximeter is used to measure SAO2. | Pulse Oximeter is used to measure SPO2. |
| Invasiveness of the Technique Used | |
| Invasive technique is used to measure SAO2. It uses the measurement of O2 saturation in arterial blood. | No-invasive technique is used to measure SPO2. It uses earlobes or fingertips for measurement. |
| Rapidness | |
| SAO2 measurement is slower than SPO2 | SPO2 measurement is raid than SAO2 |
| Efficiency | |
| Less efficient. | More efficient. |
Summary – SAO2 vs SPO2
Measurement of O2 saturation levels is very important during disease conditions to assess the respiratory levels and to check for cardiac and respiratory health. Increase or decrease of these saturation levels indicates the disease conditions. SAO2 and SPO2 differ in the method they use for measuring O2 saturation in blood. That is, SAO2 measures the total O2 bound to haemoglobin using co-oximeter whereas SPO2 measures the O2 bound to haemoglobin by pulse oximeter method. Further, SAO2 is a direct measurement of saturation of O2 in the blood while SPO2 is an indirect measurement of SAO2. This is the difference between SAO2 and SPO2.
Reference:
1.“Meaning of Blood Oxygen Saturation SpO2.” Meaning of Blood Oxygen Saturation SpO2 – HeathcareFor Home. Available here
2.Haws, Sandra. “Oxygen Saturation (SaO2).” NRSNG, 7 Sept. 2016. Available here
Image Courtesy:
1.’Co monitor’By James Heilman, MD – Own work, (CC BY-SA 3.0) via Commons Wikimedia
2.’OxyWatch C20 Pulse Oximeter’By Thinkpaul – Own work, (CC BY-SA 3.0) via Commons Wikimedia
-SAO2 is specifically the saturation of arterial O2, as opposed to SVO2 (venous).
-SPO2 levels often remain high with anemia while patient fails to perfuse tissues effectively (measures saturation of hemoglobin, which there may be too few of).