A pulse oximeter is a small, non-invasive medical device designed to measure the oxygen saturation level (SpO₂) of the blood and pulse rate. In simple terms, it tells us how much oxygen is being carried by the red blood cells to the body’s tissues. Oxygen is vital for every cell, and maintaining adequate oxygen levels is essential for the proper functioning of the heart, lungs, brain, and other organs. This device has become a household name, especially after the COVID-19 pandemic, when people began using it widely to monitor oxygen levels at home.
The Science Behind the Device
The working principle of a pulse oximeter is based on light absorption technology. It uses two types of light-emitting diodes (LEDs) — one red light (approximately 660 nm) and one infrared light (approximately 940 nm) — that pass through a thin part of the body such as the fingertip, earlobe, or toe.
The device has a photodetector on the opposite side that measures how much light passes through the tissue without being absorbed. The absorption of light varies depending on the oxygen level in the blood because oxygenated hemoglobin (HbO₂) and deoxygenated hemoglobin (Hb) absorb light differently.
Oxygenated hemoglobin absorbs more infrared light and less red light.
Deoxygenated hemoglobin absorbs more red light and less infrared light.
By comparing the absorption of these two wavelengths, the pulse oximeter calculates the percentage of hemoglobin that is oxygenated — the SpO₂ value — typically displayed on the screen as a number between 0 and 100%.
Parts of a Pulse Oximeter
A standard fingertip pulse oximeter includes:
LED sensors – Emit red and infrared light.
Photodetector – Detects transmitted light.
Microprocessor – Calculates the oxygen saturation and pulse rate.
Display screen – Shows results, often as SpO₂ and heart rate (BPM).
Power source – Usually batteries or rechargeable cells.
Normal Readings and Interpretation
A healthy person’s oxygen saturation generally falls between 95% and 100%.
95–100% – Normal range, adequate oxygenation.
90–94% – Mild hypoxemia (low oxygen levels).
Below 90% – Indicates severe hypoxemia and may require immediate medical attention.
It’s important to note that readings can fluctuate slightly due to movement, temperature, or even nail polish on the finger, which can interfere with the light signal.
Clinical and Home Applications
Pulse oximeters are widely used across various healthcare settings and at home.
1. Hospital and Clinical Use:
Operating rooms – To monitor oxygenation during anesthesia and surgery.
Intensive care units (ICUs) – Continuous monitoring of critical patients.
Emergency departments – Quick assessment of respiratory function.
Post-surgery recovery – Ensures oxygen levels remain stable.
2. Home Monitoring:
For patients with chronic respiratory or cardiac conditions, home monitoring is invaluable. Conditions like COPD (Chronic Obstructive Pulmonary Disease), asthma, sleep apnea, COVID-19, and heart failure often require regular SpO₂ checks. Early detection of falling oxygen levels allows for timely medical intervention, sometimes preventing hospitalization.
Advantages of Using a Pulse Oximeter
Non-invasive: It measures oxygen levels without drawing blood.
Instant results: Provides real-time readings within seconds.
Portable: Small, battery-operated devices suitable for home and hospital use.
Safe and painless: No discomfort or risk of infection.
Early detection: Identifies hypoxia (low oxygen levels) before symptoms appear.
Factors That Can Affect Accuracy
Several external and physiological factors can lead to inaccurate readings:
Cold fingers or poor circulation: Reduces blood flow and light detection.
Nail polish or artificial nails: Blocks light transmission.
Excessive movement: Causes fluctuations in readings.
Skin pigmentation and thickness: May slightly alter absorption patterns.
Bright ambient light: Interferes with the device’s sensors.
For the most accurate result, the patient should be at rest, with the hand warm, relaxed, and still.
The Role During the COVID-19 Pandemic
During the global COVID-19 outbreak, the pulse oximeter became an essential household medical device. COVID-19 patients often experienced “silent hypoxia,” a condition in which oxygen levels drop dangerously low without causing noticeable breathlessness. Regular monitoring with a pulse oximeter allowed early detection, enabling timely hospitalization and oxygen therapy. It played a life-saving role in countless homes and clinics worldwide.
Technological Advancements
Modern pulse oximeters have evolved with advanced features:
Bluetooth connectivity for data syncing with smartphones.
Integrated alarms for low oxygen levels.
Continuous monitoring via wearable wrist or ring designs.
Multi-parameter models that also measure respiration rate and perfusion index.
With telemedicine on the rise, these smart oximeters help doctors remotely monitor patients’ vitals.