If the doctors suspect of hypoxia, it is very common that they will recommend a very useful and non in vasive tool to assess the condition. This tool is known as pulse oximetry and it has been used ever since 1981. Pulse oximeters reduce mortality immeasurably by identifying unrecognized hypoxia.

Pulse oximetry focuses on the oxygenated and deoxygenated red cells in the absorption of red and infrared light wave lengths. So, this tool which is usually attached to the finger or wrist measures the pulsating blood and calculates how many oxygen molecules are bound to hemoglobin or oxygen saturation. In order to have good signal and accurate reading, the patient has to have a strong and regular pulse.

However, there are many patients in critical situations who have no good pulse, which results in inaccurate or fluctuating readings. Thus, besides the countless number of benefits, there are also many limitations of pulse oximetry you should know about. It is a very common practice from pulse oximeters to give false readings due to various reasons. So, some of the most common errors include intravenous dyes, lighting, patient motion, skin pigmentation, and electro surgery. 

It is known that carbon monoxide binds to hemoglobin over oxygen. Thus, it creates carboxyhemoglobin which isn’t able to bind oxygen. So, if 30% of hemoglobin binds carbon monoxide, then only 70% of hemoglobin can be saturated with oxygen. Pulse oximeters read both saturations and thus, produce an oxygen saturation reading of 100%.

The pulse oximetry readings can be inaccurate due to met hemoglobin, which depends on the concentration of the abnormal hemoglobin. It’s also important to note that if the pulse oximeter shows normal oxygen saturation levels, it doesn’t automatically rule out respiratory failure. The reason for this is that hemoglobin may remain saturated with oxygen despite hypoventilation causing rising levels of carbon dioxide. Consequently, the level of oxygen saturation may not fall below 90% until the patient is already in serious trouble. Thus, you shouldn’t rely on oxygen saturation to warn you about imminent respiratory failure.

There are a number of limitations of pulse oximetry, but the following three are considered to be the most common ones:

1. 1. If the pulse oximeter detects decreased oxygen saturation it can be a lagging indicator. This means that if are using pulse oximetry to detect respiratory failure, it probably means that the oxygen saturation monitoring is not an early warning sign but a late sign. It has often been proven that monitoring oxygen saturation can detect respiratory distress late.
2. 2. Pulse oximeters can cause false alarms. So, relying only on this tool is completely wrong as only about one third of the alarms are a true alarm.
3. 3. Pulse oximetry alone might not be sufficient or a viable strategy for high-risk patients. It can be a good strategy, but isn’t sufficient for those patients.