What is Pulse Oximeter? How does it work?

Pulse oximeters are devices that can measure the heart rate per minute and the oxygen level in the blood easily and quickly and record them when necessary. With the development of technology, it was produced in the 1970s and started to be used in hospitals. It has become one of the indispensable medical devices especially in anesthesia and intensive care units. What is Pulse Oximeter? How does it work? What are the Types of Pulse Oximeters? What is Pulse Oximeter Probe? What are the Features of Pulse Oximeters?

There are devices that measure directly from the finger, as well as devices that can measure from the forehead or ear. Working principle used to measure oxygen in the blood "To determine the oxygen rate by using the light passing through the tissue" is the principle. They are safe, painless and quick results that can be used without taking blood from the patient. There are also models that are produced in pocket sizes. There are devices that can record measurement data as well as measuring devices. The recordings can be viewed externally on the device's own screen or by connecting to a computer. On the other hand, pulse oximeters that can be connected to the Internet can record measurement data on a server. Thus, it may be possible to access all records anytime and anywhere. Pulse oximeters are used in almost every unit of healthcare facilities today. It is one of the most necessary devices in the home care process of patients.

The devices measure by using the light that passes through the tissues. This is the general working principle. There are sensors on the devices, consisting of a light source and a sensor. The measurement is provided by placing organs such as fingers or earlobes between the sensor apparatus.

Pulse oximeters work by color analysis according to whether the hemoglobin in the red blood cells absorbs oxygen or not. Sensors use the color of the blood to detect the oxygen rate. The color tone of the blood changes depending on the oxygen carrying amount of the red blood cells. The device sends red and infrared light on one side, and provides measurement thanks to the sensor on the other side. Oxygenated blood is bright red in color and absorbs most of the light sent from the pulse oximeter. Thanks to the measurement of the amount of light reaching the opposite side, the oxygen saturation in the blood is determined.

Although the oxygen saturation value obtained using pulse oximetry is very close to the value obtained by arterial blood gas analysis, the data obtained by arterial blood gas analysis are considered more accurate. With the arterial blood gas analysis, the oxygen saturation parameter (SpO2) can be measured, as well as the partial oxygen pressure (paO2) parameter. Oxygen saturation (SpO2) and partial pressure of oxygen (paO2) can be mixed with each other. Although these two parameters are related to oxygen, they express different values. Pulse oximeters measure oxygen saturation (SpO2). Arterial blood gas analysis is required for partial oxygen pressure (paO2) measurement.

Along with the oxygen saturation in the blood, heart rate per minute can also be measured by pulse oximeters. Sensors in the device determine the number of beats per minute of the arteries. Thus, the patient's pulse can also be viewed. The higher the quality of the sensor, the higher the measurement accuracy. Better quality devices should be preferred especially in pediatric patients. Otherwise, erroneous results may be encountered.

Pulse oximeters are medical devices that show vital parameters. Therefore, a pulse oximeter model suitable for the patient should be used.

What are the Types of Pulse Oximeters?

Pulse oximeters are varied according to their features. There are varieties that can be used mobile with battery or battery. Some devices have an alarm feature. Vital parameter limits that are critical for the patient are recorded in the device and when the device measures outside these limits, it gives an audible and visual alarm. This feature is an alert system for emergencies. Pulse oximeters are divided into 4 types according to their usage:

• Finger type pulse oximeter
• Handheld pulse oximeter
• Wrist type pulse oximeter
• Cantilever type pulse oximeter

All pulse oximeters measure with similar methods. The difference in devices is features such as sensor quality, battery, and alarms. There are also some external conditions that affect the use of these devices. In order to be affected by them as little as possible quality pulse oximeters should be preferred. Inaccurate measurements may cause unnecessary intervention to the patient when he is not needed, or not being intervened when there is a risky situation. In such cases, the patient's life may be endangered.

What are the Causes Affecting the Measurements?

• Movement or shaking of the patient
• Cardiac changes
• Use on hairy or dyed skin
• The environment where the device is located is too hot or cold
• The patient's body is too hot or cold
• Device and sensor quality

What are the Features of Pulse Oximeters?

Finger type pulse oximeters can be found in the market at very affordable prices. It is also very simple to use. These products, which weigh 50-60 grams, are generally battery operated. Some devices give a low power warning on their screen when the battery power is low. There are also devices that automatically turn off after about 7-8 seconds of inactivity to preserve the life of the battery.

Hand type, wrist type and console type are usually battery powered. Some models of this type of product may be battery operated. There are even devices that can be powered by both battery and battery. Usually they have large screens and alarms. Some pulse oximeters also have features such as blood pressure or thermometers. These features are usually found in console type devices.

Handheld pulse oximeters are sized to be held in the palm. It can also be used on the table or hanging on the IV pole. It is larger than finger type devices and the sensor is connected externally via a cable. Wrist type pulse oximeters, on the other hand, are slightly larger than a wrist watch and are used by attaching to the wrist like a wrist watch. Since it is fixed on the wrist of the patient, there is no risk of the device falling to the ground. As in hand-held models, the sensor is connected externally to the device via a cable.

Cantilever type pulse oximeters are considerably larger than others. Since its case is large, it may have a larger battery and screen than other models. Thus, it can provide longer use in power cuts. The large screen also allows parameters to be controlled more remotely. It can be used on a table or a coffee table. In console type devices, the sensor is connected externally via a cable.

Since they can be used in emergency situations, pulse oximeter models resistant to impact and liquid contact have been produced. There are also devices that can be used in the MR room. They are resistant to radiation, can be used during MRI and do not cause any artifacts in the MR image.

What is Pulse Oximeter Probe (Sensor)?

Sensors used in pulse oximeters and performing the measurement process are called “pulse oximeter probe”. These are used by adding externally to console type, wrist type and handheld devices. There is no need for a separate sensor in finger type devices, the sensor is integrated on the device.

Pulse oximetry probes are available in disposable (single use) or reusable (reusable) models. Reusable ones are made of silicone and can be autoclaved sterilized. Disposable ones are for single use and cannot be sterilized and reused. Disposable pulse oximetry probes, if used with care, will measure accurately for approximately 1-2 weeks. It must then be replaced with a new one. Reusable probes can generally be used between 6 months and 1 year. These are accessories used with pulse oximeters, they have different types of features and the type to be used is determined by the patient's condition.

Three sizes of probes are produced as neonatal, pediatric and adult. In order to get accurate measurement results, the appropriate size should be selected for the patient's weight. Generally, disposable ones are used in babies. Since these are sticky, even if the baby is moving, the sensor stays still and the device can continue to measure without any problems. Measuring problems may also occur when using a reusable probe in highly mobile adult patients.

There are probes suitable for different brands of devices in the market. The appropriate probe should be selected instead of inserting the sensor socket of the pulse oximeter. Technologies of the "Nellcor" and "Masimo" brands are mostly used in the market. Therefore most probes are compatible with these brands. Measurement results may be inaccurate when using a sensor that is not suitable for the device. Since this situation may pose a life-threatening risk, probes suitable for the patient and the device should be preferred.