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SpO2 oxygen saturation pulse oximetry definition normal values
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SpO₂ (Oxygen Saturation)
SpO₂ stands for peripheral capillary oxygen saturation, measured non-invasively by a pulse oximeter. It reflects the percentage of haemoglobin (Hb) molecules in the blood that are bound to oxygen — i.e., how much oxygen the blood is carrying relative to its maximum carrying capacity (Bailey & Love's Surgery, 28th Ed., p. 999).
How It Works
A pulse oximeter clips onto a peripheral site (usually a fingertip or earlobe) and emits two wavelengths of light (red ~660 nm and infrared ~940 nm). Oxyhaemoglobin and deoxyhaemoglobin absorb these wavelengths differently, allowing the device to calculate the ratio and display SpO₂ as a percentage.
Normal Values
| Category | SpO₂ Range |
|---|---|
| Normal (healthy adult) | 95–100% |
| Acceptable (some clinical contexts) | ≥94% |
| Mild hypoxaemia | 90–94% |
| Moderate hypoxaemia | 75–89% |
| Severe hypoxaemia | <75% |
A reading below 94% typically warrants clinical assessment; below 90% is generally considered a threshold for supplemental oxygen intervention.
SpO₂ vs SaO₂
| Term | Meaning | Method |
|---|---|---|
| SpO₂ | Peripheral O₂ saturation | Pulse oximetry (non-invasive) |
| SaO₂ | Arterial O₂ saturation | Arterial blood gas (invasive) |
SpO₂ is a close approximation of SaO₂ but can diverge in certain conditions.
Causes of False or Inaccurate Readings
- Poor peripheral perfusion (shock, hypothermia, vasoconstriction)
- Motion artifact
- Nail polish or dark pigmentation (particularly affects some devices)
- Carbon monoxide poisoning — carboxyhaemoglobin reads falsely high
- Methaemoglobinaemia — SpO₂ tends to read ~85% regardless of true saturation
- Anaemia — does not directly falsify SpO₂, but O₂ content can still be critically low
- Jaundice / bright ambient light — can interfere with optical sensors
Clinical Significance
- SpO₂ is a core vital sign used continuously in ICU, anaesthesia, emergency, and ward settings
- Guides oxygen therapy titration (target SpO₂ 94–98% in most patients; 88–92% in hypercapnic COPD patients to avoid suppressing hypoxic drive)
- A sudden SpO₂ drop is an early warning of respiratory deterioration, airway compromise, or haemodynamic instability
Limitations
SpO₂ only reflects haemoglobin saturation — it does not directly measure:
- PaO₂ (partial pressure of oxygen)
- Ventilation (CO₂ levels)
- Oxygen delivery (which also depends on cardiac output and Hb concentration)
For a complete picture of oxygenation and ventilation, an arterial blood gas (ABG) is required.
Xray paper name to take photos
This is not a medical query — it's about photography/imaging materials. I'll answer directly from general knowledge.
The paper (or film) used to take X-ray images is called:
Radiographic Film (X-ray Film)
The specific types include:
| Name | Description |
|---|---|
| Silver Halide Film | Traditional X-ray film; uses silver bromide crystals that react to radiation |
| Blue-sensitive film | Used with blue-emitting intensifying screens |
| Green-sensitive (Ortho film) | Used with green-emitting rare-earth screens (most common in modern radiology) |
| Direct Exposure Film | Used without screens, for fine-detail imaging (e.g. dental, extremities) |
| Duplicating Film | Used to make copies of existing X-ray films |
Key Brands / Trade Names
- Kodak (Carestream) — e.g., Kodak T-MAT, Kodak X-Omat
- Fujifilm — e.g., Fuji Super HR, Fuji UR
- Agfa — e.g., Agfa Cronex, Agfa Structurix
- Konica — e.g., Konica SRO
Modern Alternative
Most hospitals today have shifted to digital radiography (DR) or computed radiography (CR), replacing physical film with:
- Phosphor imaging plates (CR)
- Flat-panel digital detectors (DR)
In this case, no physical film is used — images are captured and stored digitally.
If you're asking about a specific use case (dental, chest, industrial, etc.), let me know and I can narrow it down.
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