Pulse Oximetry

Pulse oximetry is a non-invasive medical test used to monitor the oxygen saturation of a patient's blood, as well as their heart rate.

How it Works

Pulse oximetry uses a device called a pulse oximeter, which consists of a sensor attached to a finger or toe. The sensor emits two different wavelengths of light: red and infrared. Hemoglobin in the blood absorbs these lights differently depending on its oxygenation state.

Principle

The principle behind pulse oximetry is based on the difference in absorption of red and infrared light by oxyhemoglobin (oxygen-rich hemoglobin) and deoxyhemoglobin (oxygen-poor hemoglobin). Oxyhemoglobin absorbs more infrared light, while deoxyhemoglobin absorbs more red light.

Components of a Pulse Oximeter

• Sensor: This is the part that is attached to the patient's finger or toe. It contains the light-emitting diodes (LEDs) and photodetector.
• Monitor: This displays the oxygen saturation level, heart rate, and sometimes other parameters such as perfusion index.

Interpretation of Results

The results from a pulse oximeter are typically displayed as:

• SpO2 (peripheral capillary oxygen saturation): This is the percentage of hemoglobin that is saturated with oxygen. Normal values are usually between 95% and 100%.
• Heart Rate: The number of heartbeats per minute, which should fall within a normal range depending on age and other factors.

Clinical Applications

Pulse oximetry is widely used in various clinical settings for:

• Monitoring patients during surgery or under anesthesia.
• Evaluating patients with respiratory diseases, such as chronic obstructive pulmonary disease (COPD) or pneumonia.
• Assessing the need for supplemental oxygen therapy.

Limits and Potential Errors

Pulse oximetry has limitations and potential sources of error, including:

• Movement artifacts: Patient movement can interfere with the signal.
• Nail polish or skin pigmentation: Certain colors of nail polish or darker skin tones can affect the accuracy of readings.
• Low perfusion states: In conditions where blood flow to the extremities is compromised, pulse oximetry may not provide accurate readings.

Maintenance and Calibration

Pulse oximeters require regular maintenance and calibration to ensure accuracy. This includes checking the sensor for damage, cleaning the device, and performing quality control checks as recommended by the manufacturer.

Frequently Asked Questions (FAQs)

What is pulse oximetry?
A non-invasive test measuring oxygen saturation in blood.

How does pulse oximetry work?
Using light to measure changes in blood oxygen levels.

Where is a pulse oximeter typically placed?
On the finger, toe, or earlobe.

What is being measured by a pulse oximeter?
Oxygen saturation and heart rate.

Is pulse oximetry painful?
No, it is painless.

How long does a pulse oximetry test take?
Only a few seconds to a few minutes.

Can anyone use a pulse oximeter?
Yes, including adults and children.

What are normal pulse oximetry readings?
Oxygen saturation above 95% on room air.

Are there any risks associated with pulse oximetry?
Generally none, as it is non-invasive.

Why is pulse oximetry used in medical settings?
To quickly assess oxygen levels and heart rate.