Pulse Oximeter: What It Measures, Normal Values, and Types
Pulse Oximeter: What It Measures, Normal SpO₂ Values and Types of Devices
Everything you need to know about the pulse oximeter: how it works, what readings are normal and when to seek emergency care. Guide for professionals and patients in Colombia.
Reviewed by medical technology specialists · GSMED Imaging ColombiaThe pulse oximeter —also called a pulse oximeter— is one of the most widely used medical devices in the world. By simply placing a sensor on the finger, ear or wrist, it measures in real time the blood oxygen saturation (SpO₂) and heart rate, without the need to draw blood or perform invasive procedures.
During the COVID-19 pandemic, the oximeter became an essential home device: "silent hypoxemia" —a severe drop in oxygen without obvious symptoms— was one of the most important warning signs in patients with SARS-CoV-2 pneumonia. Today, its use goes much further: it is essential in ICUs, surgery, emergency rooms, medical offices, veterinary clinics and homes of patients with COPD, heart failure or sleep apnea.
In Colombia, where cities like Bogotá are located at altitudes of over 2,600 meters, understanding normal SpO₂ values has particular clinical implications that this article addresses in detail.
How does the pulse oximeter work?
The physical principle that makes pulse oximetry possible is called photoplethysmography: the device emits two beams of light —one red (660 nm) and another infrared (940 nm)— through the tissue (usually the finger) and a photodetector measures how much light passes through to the other side.
The key is that oxygenated hemoglobin (HbO₂) and deoxygenated hemoglobin (Hb) absorb light differently:
🔴 Red light (660 nm)
Deoxygenated hemoglobin absorbs more red light. That is why venous blood (without oxygen) looks darker. The oximeter uses this difference to calculate how much Hb is not saturated.
💡 Infrared light (940 nm)
Oxygenated hemoglobin absorbs more infrared light. Well-oxygenated arterial blood appears bright red because it reflects this wavelength more.
The oximeter's microprocessor calculates the ratio between the absorption of both wavelengths during the arterial pulse (that is why it is called "pulse": it only analyzes the pulsatile component, which corresponds to arterial blood, discarding the light absorbed by tissues, venous blood and skin).
The result is the SpO₂: percentage of hemoglobin that is saturated with oxygen. A value of 98% means that 98% of the hemoglobin binding sites are occupied by O₂ molecules.
🔬 Technical data: The sensor also detects the heart rate by analyzing the regularity of the arterial pulses. That is why the oximeter shows two values simultaneously: SpO₂ (%) and HR (bpm).
Table of normal SpO₂ values
Normal oxygen saturation ranges vary depending on age, clinical condition and —especially in Colombia— altitude above sea level.
| Population / Condition | Normal SpO₂ | Alert | Action |
|---|---|---|---|
| Healthy adult (sea level) | 95 – 100 % | 90 – 94 % | Clinically evaluate |
| Healthy adult in Bogotá (~2,600 m) | 92 – 98 % | 88 – 91 % | Evaluate symptoms and context |
| Stable COPD patient | 88 – 92 % | < 88 % | Adjust supplemental O₂ |
| Full-term newborn | 95 – 100 % | < 95 % | Immediate neonatal evaluation |
| Children (1–12 years) | 95 – 100 % | 91 – 94 % | Urgent medical consultation |
| Any patient — emergency | < 90 % → EMERGENCY ROOM | < 85 % critical | Immediate oxygen + transfer |
🏔️ Note on altitude in Colombia: In Bogotá (2,600 m), Manizales (2,150 m) and other high-altitude cities, atmospheric pressure is lower and the partial pressure of oxygen is lower. That is why it is normal for acclimatized residents to have SpO₂ between 92–96 %. A value of 93 % that would be concerning in Barranquilla can be completely normal for a healthy person from Bogotá. The doctor should always interpret the figure in clinical and geographic context.
Factors affecting the oximeter reading
The pulse oximeter is a reliable device, but several conditions can produce falsely low readings (false negatives) or falsely normal readings (false positives). Knowing them is essential to correctly interpret the results:
Dark polish (black, blue, green) can absorb light and falsely reduce SpO₂. Solution: rotate the sensor 90° (side of the finger) or remove the polish from the measuring finger.
Cold or hypoperfusion (shock, sepsis) reduces arterial flow in the fingers. The sensor does not detect the pulse well and produces erroneous readings or "no signal". Warming the hands improves the signal.
Motion artifact is the most frequent cause of erroneous readings. Professional-grade oximeters with Masimo SET® or Nellcor OxiMax® technology filter movement better.
Paradoxically, a normal SpO₂ with severe anemia can hide very deficient O₂ transport. The oximeter measures the % of saturated hemoglobin, not the total amount of hemoglobin available.
Direct sunlight or neonatal phototherapy lamps can saturate the photodetector. Covering the sensor with a dark towel or using opaque cover sensors solves the problem.
Hemoglobin bound to carbon monoxide absorbs light similarly to oxyhemoglobin. The standard 2-wavelength oximeter does not detect CO poisoning and can show normal SpO₂ in a severely poisoned patient.
Types of pulse oximeters
Oximetry technology has evolved to adapt to different clinical environments and monitoring needs:
Finger oximeter (clip)
The most common and economical. It is placed on the pad of the index or middle finger. Available in disposable (hospital) and reusable (home/clinic) versions. Ideal for spot measurement.
Use: Medical offices, emergency rooms, home, triage.
Wrist Oximeter
Allows continuous monitoring for hours or days. Used in sleep apnea studies, cardiopulmonary rehabilitation, and prolonged home monitoring. Professional models store data for later analysis.
Use: Sleep apnea, home COPD, rehabilitation.
Integrated in Multiparameter Monitor
Oximetry is one of the standard parameters in ICU, operating room, and recovery room monitors. It connects via reusable or disposable (adhesive) probes to the finger or earlobe for continuous monitoring with configurable alarms.
Use: ICU, operating room, delivery room, ambulance transport.
Neonatal and Pediatric
They use special adhesive probes for the foot, hand, or finger of the newborn or small child. They require greater precision and sensitivity to movement. They are essential in neonatal ICU (NICU) and critical pediatrics.
Use: NICU, neonatology, hospital pediatrics.
SpO₂ vs SaO₂ vs PaO₂: What's the difference?
Three terms that appear frequently in clinical reports and should not be confused:
| Parameter | What it measures | How it is obtained | Normal value |
|---|---|---|---|
| SpO₂ | Estimated oxygen saturation in peripheral capillary blood | Pulse oximeter (non-invasive) | 95–100 % |
| SaO₂ | Actual oxygen saturation measured in arterial blood | Arterial blood gas (invasive) | 95–100 % |
| PaO₂ | Partial pressure of oxygen dissolved in arterial plasma | Arterial blood gas (invasive) | 80–100 mmHg |
💡 Clinical relationship: SpO₂ and SaO₂ usually differ by only 1–2 percentage points under normal conditions. Arterial blood gas (SaO₂ and PaO₂) is the reference standard, but requires arterial puncture. The oximeter offers a continuous and non-invasive estimate that is sufficient for most clinical decisions, but in case of significant clinical doubts, arterial blood gas remains the gold standard.
Oximeters for medical vs home use
Not all oximeters are the same. The difference between a certified medical-use device and a consumer device can be clinically relevant:
✅ Medical / hospital use
- • FDA or CE Class IIb certification
- • Accuracy ±2 % at SpO₂ 70–100 %
- • Advanced motion filtering technology
- • Configurable alarms and exportable logs
- • Compatible with pediatric and neonatal probes
- • Certified maintenance and technical support
⚠️ Home / consumer use
- • Variable certification (many without clinical validation)
- • Accuracy ±3–5 % (can differ significantly)
- • No robust motion filtering
- • No configurable clinical alarms
- • Not suitable for critical therapeutic decisions
- • Useful for home monitoring guidance
Do you need oximeters or monitors for your institution?
We advise on selection according to the volume of patients and the level of complexity of your institution in Colombia.
Request free consultation →Frequently asked questions about the pulse oximeter
We answer the most common questions from patients and healthcare professionals.
