Oxygen (O2) is transported from those lungs to the cells by the blood. O2 is both fixed to hemoglobin or free in the blood. However, the amount of free O2 in that blood is minimal compared to O2 fixed to hemoglobin, plus free O2 does not participate significantly in the total oxygen content in significant blood.
Therefore, the oxygen content in the blood can be reduced with either decreasing hemoglobin concentration or by reducing the dimension of hemoglobin with O2 fixed. This proportion is called the hemoglobin oxygen saturation in some arterial blood (SpO2).
A pulse oximeter is ready to measure SpO2 if the device can detect a pulse. However, it does not charge hemoglobin saturation. This device also calculates heart rate. A photoplethysmographic curve can also do provided on some monitoring devices. It describes the variation of the diameter of the arteries over time.
Figure 1: Waveform obtained from the pulse oximeter
The box by orange text gives data obtained from the sign analysis, such as heart rate (109) plus oxygen saturation (94). Notice the words “small signal” circled into red below the heart rate. It indicates a signal of poor quality too though the waveform looks normal. The amplitude of the waveform does not match the quality of the signal as the gain is usually adjusted automatically.
Pulse Oximeter Benefits
- Quick and easy to use
- Continuous monitoring
- Audible signal
Pulse Oximeter Disadvantages
- Late alert for respiratory problems: Hemoglobin is already 100% saturated while breathing room air (21% O2). Therefore, even by raising the quantity of O2 breath, SpO2 does not go above 100% under anesthesia (100% O2).
- Numerous factors can affect the reading:
Such as pulse quality, movement of the patient, skin or mucosa pigmentation, plus ambient light. The amplitude of the waveform does not consider the quality of the signal as the gain means often adjusted automatically; therefore, it should not be used to assess the significant quality of this signal and data.