How SpO₂ sensors (Pulse Oximeter) are useful in identifying Covid severity?

SpO2 pulse oximeter sensor

Pulse Oximeter sensors (SpO₂ Sensors) have been always hitting the headlines ever since the emergence of Covid 19 pandemic.

So, Why is there an upsurge in demand for these Pulse Oximeter SpO₂ Sensors? Well, SpO₂ sensors play a pivotal role in measuring the heart rate and blood oxygenation levels in your body.

Be it a home, hospital, medical center or critical care setup, currently, Pulse oximeters are the massive game changers, being the non-invasive and fast method in the primary assessment of oxygenation levels in human blood.


The blog throws light on 

1. Pulse Oximeter Sensor for Covid Detection

2. How Accurate are SpO2 Sensor?

3. What is the right way to use Pulse Oximeter Sensor? ( Correct Placement of SpO2 sensor )

1. Pulse Oximeter/ SpO2 sensor for Covid Detection:

When a person contracts Covid Pneumonia or silent pneumonia, there arises a mild to serious complication of Novel Covid virus infections around the lungs air sac. This condition inturn causes low blood oxygen levels, even with or without difficulty in breathing.This condition is known as Silent Hypoxia which is quite commonly occurring symptom of Covid.

Here’s where these sensors come into the picture to throw the spotlight on your oxygen level metrics even before your realisation on covid contraction. 

 A Good SpO₂ sensor signals the abnormalities and warning risks of the covid patients. On the other hand, the detection of abnormal blood oxygen levels in Adults, Pediatrics, neonates and premature-neonates who have been affected by covid can be done using good pulse oximetry systems.

2. The next question pops in minds “How accurate are SpO₂ sensors"?

Currently, there is an ongoing debate questioning the accuracy levels of the  sensors. Various SpO₂ sensor technology advancements such as in light emitting diodes, microprocessors have enhanced the clinical performance.

It is often noted that medical grade SpO₂ sensors are generally more efficient than the home portable pulse oximeters. In Spite of pulse oximeter sensors undergoing rigorous medical testing and certifications, the clinical results may vary occasionally as per WHO report. The article provides you the useful insights of choosing the accurate sensors for blood oxygen saturation monitoring. 


The fairly accurate SpO₂ readings hold true specifically when best quality sensors are employed in any settings. The Pulse Oximetry Training Manual by World Health Organisation states that once the oximeter is clipped on the fingers, it must be given a 10 seconds time interval to obtain the best accurate readings, thus handling with utmost patience.

SpO₂ Sensors, pulse oximeter, SpO₂ sensor covid, SpO₂ sensor benefits, pulse oximeter benefits, pulse oximeter accuracy
The image illustrates the SpO₂ sensor working principle.

Can SpO₂ sensors give false reading ?

Well, yes. The accuracy is greatly influenced by many factors.

So, What are the factors that cause false reading on Pulse Oximeter sensor?


Factors that affect the accuracy of Pulse Oximeter / SpO2 Sensors

 1.Body Peripheral application site

Normally the SpO₂ levels are measured at the peripheral sites of the human body mainly toes, fingers, ear and forehead. While one is facing breathing problems or suspecting Covid, to level up the chance of accurate readings, the sensors can be used at the peripheral site that are sufficient for blood perfusion.

The fingers are the viable options to be used in the medical grade sensors in order to get precise readings due to the less shaky movements and better blood perfusion. 

According to the study, the middle finger of the dominant hand is useful in displaying significant SpO₂ results. However, poor blood perfusion sites, extreme cold conditions of the patient and Vasoconstriction (limits the blood flow to the peripheral sites) cause failure in recording the levels. 

2. Proper Application of the SpO₂ sensor

Usage of correct SpO₂ sensors are extremely essential to achieve precision in the readings. Make sure the sensor properly fits the application site. Loose fitting sensors can result in preventing the passage of light from emitter to the site (optical bypass).

Whereas, Tight fitting sensors can cause venous pulsation (CPR). Both scenarios can provide discrepancy in the blood oxygen levels. To avoid pseudo reading, the sensor probes should be aligned at the heart level.

3. Role of Motion artefacts

Shivering, shaking, standing positions, exercise, physical strenuous activities, seizures and unstable positions leads to erroneous measurements due motion artefacts. In such cases, either rectification in the stable positions for re-reading or clinical assessments can be sought.

Conversely, psychological factors such as shock, fear and anxiety may produce false  SpO₂ sensor alarm readings.Moreover, in low blood pressure cases due to low cardiac output, the sensors fail to detect the weak pulse signals.Poor signals can be detected when mechanical interference with blood circulation (restricted clothes, blood pressure cuffs), thus causing inaccuracy results. 

Normally, pulse oximeters attached to the person who is sitting upright has the chance of getting high oxygenated saturation levels compared to the other one in a reclining/ laying down position. Utilising the benefits of a motion tolerant sensor can gain significant clinical performance.

4. Nail Polish/ Art

While detecting the SpO₂ levels of Women with gel or acrylic shiny glittery nail polish, nail arts, and henna dye, there are high possibilities of misleading readings. Even though, the pulse oximeter detects the pulse waveforms, the pigments in nail color/art/artificial nail acts as a barrier in blocking the signals. In a nutshell, it is advisable to remove the nail polish or in unavoidable emergency cases, it is better to use another peripheral site such as ear lobes.

5. Effect of Lighting 

Bright lights such as sunlight, high intensity radio sources, fluorescence light, operation theatre, infrared light etc does cause an impact on the blood oxygen levels variation due to ambient level interferences. Alternatively, it is crucial to wrap/ shield the SpO₂ sensor probes with black material as it blocks the radiation from the light sources. By shielding process, the inaccuracy results can be avoided.

6. Skin Pigmentation 

Though skin pigment Melanin can absorb a significant amount of light radiation, the report by Food Drug Administration depicts that SpO₂ accuracy levels differ between the dark skin and white skin pigmentations.

The accuracy difference readings are usually slightly smaller when the oxygenated saturation levels are above 80% and greater while the oxygenated levels are below 80%.

Further scientific evidence should be backed up to address the accuracy and reliability factors. Erroneous oxygenated levels might also arise due to the skin thickness and poor blood circulation.

7. Smoking, Medication

Carbon monoxide levels increases right after the person smokes a cigarette or was on the smoky fire environment.The carbon monoxide from the smoke combines with the haemoglobin and oxygen displacement happens to form carboxyhemoglobin.

Carbon monoxide poisoning can lead to flawed readings of oxygenated levels.Besides, certain medications such as nerve blockers can impede the accuracy results of the clinical performance. 

3. So, What is the right way to use Pulse Oximeter Sensor? 

 Correct Placement Of pulse oximeter sensor:

Here's a video on the correct placement of pulse oximeter sensor and the consequence of improper placement of SpO2 sensor or usage of wrong SpO2 sensors types.



Even though the calibration of pulse oximeters sensors are the integral part of standardised procedures, it is really the need of the hour to realise that working of SpO₂ sensors in clinical setup must adhere to the manufacturer’s accuracy specifications. 

While purchasing/replacing sensors for the oximeters, utmost importance should be given to whether the manufacturer’s SpO₂ sensors complies to the valid certifications, biocompatibility specifications, regulations, and standard practices.

Wise decisions can be made by buying oxygen saturation sensors from a manufacturer, no matter be it a compatible manufacturer or OEM, who complies with EN ISO 80601-2-61. 

It is highly crucial to purchase from a reliable manufacturer with a track record of transparency in the materials used in the manufacturing process and also with a solid proof of positive ratings.

In addition, during the current pandemic, getting yourself associated with good manufacturers who do not overcharge the sensors price is certainly an essential factor to be considered.

Let’s not fall into the prey of non-approved, unreliable and inaccurate clinical SpO₂ sensors /Pulse Oximeters.


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