Readings and Reliability of Pulse Oximeter Results

For many years, there is no doubt that the pulse oximeter is a revolutionary innovation in patient care because of its unique advantage on continuously monitoring the cardiac and respiratory status of a person.

Oxygen saturation is defined as the amount of oxygen dissolved in the blood, specifically the amount bound to hemoglobin, expressed in percentage. Human blood typically consists of four types of hemoglobin: oxyhemoglobin (O2Hb), reduced hemoglobin (Hb), methemoglobin (MetHb), and carboxyhemoglobin (COHb). The pulse oximeter is designed to measure the amount of oxyhemoglobin, but if methemoglobin and carboxyhemoglobin are present in large quantities, the results would become erroneous.

Interpretation of the Results

After properly wearing the probe, the device will display a number that will indicate the amount of oxygen saturation. A healthy human has a normal blood oxygen saturation value (SpO2) between 95 to 100% (value varies depending on literature used). Should the results go below 90%, the person will be given supplementary oxygen, and he/she will be further evaluated for signs of marked hypoxia.

Accuracy

There are particular limitations to the accuracy of the pulse oximeter to predict oxygen saturation. The accuracy of pulse oximeters vary extensively, most likely due to the different methods or algorithms utilized in calculating the light signals. Generally, oximeters are capable of generating precise readings within oxygen saturations ranges of 80 to 100% and less accurate below 80%.
On rare occasions, the readings may not be accurate. As mentioned under the page dedicated to limitations, clinical conditions may give rise to inaccurate readings, and therefore should be taken always in consideration. The probes may even become a factor in the accuracy, such as in the case of surgery or peripheral arterial occlusion where fingertip probes may have lower accuracy than ear probes.

In some situations, oximeters might have problems. But similar to most monitoring equipment, the results should at all times be viewed in view of the person’s medical condition. One should not neglect a reading that indicates that the person is starting to be hypoxic.