How to differentiate between good Pulse Oximeter sensors and the bad ones
This is Arunkumar Chidambaram, representing Biometric Cables, a company engaged in manufacturing of SpO2 Sensors for the past 12 years. I am No scientist but have gained expertise from my manufacturing experience to genuinely differentiate between good Pulse Oximeter sensors and the bad ones.
This article is a brief explanation on the factors affecting the clinical and functional requirements of the above mentioned SpO2 Sensors and how to choose a right one.
"FDA & ISO 80601-2-61 describes Pulse Oximeters as a system (They comprise of the sensor and oximeter itself). Every new or modified system should be clinically validated for individual and combined properties unless adequate scientific justification can be provided in lieu of this testing".
Life Span of a Pulse Oximeter is around 5-7 years, whereas the SpO2 sensors will last not more than 1 to 1.5 years upon regular usage. In today’s scenario, more than 50% of the Patient Monitors and Pulse Oximeters users buy compatible sensors for the simple reason that they are cost-effective and have interchangeability. But do the users really know what is at stake? Take a look at it.
For easy and systematic understanding, I have created six subheadings, which are
1. Why are SpO2 or Pulse Oximeter readings important?
2. What is the working principle of Pulse Oximeter and its sensors?
3. Functional requirements of a SpO2 sensor?
4. How does it affect clinical findings?
5. Myths in choosing a perfect SpO2 sensor
6. How to choose the right one?
- Why are SpO2 or Pulse Oximetry readings important?
We all know the importance of Oxygen for the survival of human beings. Pulse Oximetry is a non-invasive method of measuring the Oxygen saturation in the blood stream. Its use in the assessment of respiratory functions in the human body makes it a vital parameter in patient monitoring. And, for these very reasons FDA has classified these products under Class II while EU MDD has classified it at class II A.
- What is the working principle of Pulse oximeter and its sensors?
Before the invention of Pulse Oximeter, the practice was to draw blood from patients and analyse the samples at regular intervals in a day using large laboratory equipment such as blood gas analyser. Blood gas analysers determine the partial pressure of Oxygen in the blood (pO2) by means of chemical sensors, and they directly measure the ratio of the oxygenated haemoglobin to the total haemoglobin in a sample of blood SaO2 (Arterial Oxygen Content).
The Pulse Oximeter was invented in 1980s. They made use of the pulsatile arterial blood flow, generated by the heart, by emitting light rays of two different wavelengths, red at 660 nm and infrared at 940 nm. The small size of LEDs and photodiodes make it possible to mount the optical components directly on the sensor for use in patient non-invasively.
The definition of SpO2 can be stated by a simple equation
SpO2 = [HbO2] / [Hb][HbO2]
Where, HbO2 is concentration of oxygenated haemoglobin
Hb is concentration of haemoglobin
SpO2 is saturation of oxygen
- What are the functional requirements of a SpO2 sensor?
According to FDA 510 k and ISO 80601-2-61, here are the prerequisites for basic safety and essential performance of Pulse Oximeter equipment - “SpO2 Sensors should be validated for affected combined properties and at least include high Accuracy, EMC, electrical safety, and protection against excessive temperature and separately testable properties for sensors, like bio-compatibility”
- How does it affect clinical findings?
The Pulse Oximeter reading is one of the minimum requirements for monitoring during anaesthesia. Pulse Oximeters are often used to guide therapeutic interventions. The British Thoracic Society guidelines on the use of emergency oxygen in adults state that treatment should be targeted to oxygen saturation. Hence, it is important for pulse oximeter probes to be accurate in order adapt right procedures. Any Pulse oximeter probe with inappropriate design of LEDs, photo sensors, cables, connectors, housings will deter EMC, electrical safety of the pulse oximeter itself. An amateurish sensor may inflict allergies to patients if not tested for its bio-compatibility.
Myths in choosing a perfect SpO2 Sensor
Most Buyers tend to choose the right SpO2 Sensors for themselves based on the following factors.
- Clinical performance using functional generators
- Price of SpO2 sensors
- Clinical performance of SpO2 sensors
Myth: A SpO2 sensor is deemed good if it passes the functional generator test.
Clinical performance of a SpO2 sensor is tested with the help of functional testers (Simulators or Calibrators) which is not recommended by ISO 80601-2-61 for a simple reason for its limited ability to determine whether the pulse oximeter probe is performing as the manufacturer designed it to perform and can never determine whether the design was correct. Detailed Elaboration on this point can be found in ISO 80601-2-61 Clause FF 3.
- Price of SpO2 Sensors
Myth: OEM sensors and compatible sensors perform the same intended function; then why pay the high price.
In present scenario, OEM sensors costs almost 7-8 times the price of compatible SpO2 sensors, justifying their pricing by adhering to the regulatory requirements. However, almost 90-95% of the compatible SpO2 sensor manufacturers present in today’s market
lack the basic requirements of ISO 80601-2-61. Absence of regulations in certain countries helps manufacturers like these to create confusion among the customers and prospective buyers about the price. They use this gap of “absence of regulation” combined with half-truths of “testing the SpO2 sensors for accuracy with functional generators”, to sell a sub-standard, clinically unworthy products.
Are all the compatible SpO2 manufacturers unfit to use?
NO, there are good manufacturers who do a really good product by adhering to regulatory norms and justified pricing.
- Reliability of SpO2 Sensors
The term reliability is defined as “The ability of a SpO2 sensor to consistently perform its intended clinical function on demand and without degradation or failure over the stated period”
It is highly dependent of the following parameters
- Manufacturing processes
- Raw materials used
Hence, it is ideal to directly buy the sensor from the manufacturer who practises a valid
ISO 13485 than to buy it from a trader who may not be able submit necessary testimonials.
A short video that depicts the integral parts of a SpO2 sensor that helps to identify the reliable parts versus the unreliable ones.
- How to choose the right one?
As mentioned earlier, the accuracy of a pulse oximetry readings are combination of Pulse oximeter and its sensors, if the customer wants to change to compatible sensors instead of OEM sensors, the following should be verified.
- Accuracy statement and method claimed by the manufacturer of the sensor
- Bio-compatibility requirements
- Certifications and standards are adhered to
Summary: The market is flooded with many types of SpO2 sensors from different manufacturers. Therefore, it is the responsibility of a physicians, biomedical engineers, and competent purchase officers to identify the right ones in order to save the life of their patients, who they have been entrusted with.