In Pulse Oximetry, the device differentiates between oxygenated and deoxygenated hemoglobin based on the absorption of:

Appeared in: RML Lucknow - 2021

Explanation

Pulse oximetry operates on the principle of spectrophotometry, using light to measure the concentration of a substance.
The device emits two specific wavelengths of light: red light (approx. 660 nm) and infrared light (approx. 940 nm).
Oxygenated hemoglobin (HbO₂) and deoxygenated hemoglobin (Hb) have different light absorption characteristics at these two wavelengths.
HbO₂ absorbs more infrared light, while Hb absorbs more red light.
The oximeter calculates the ratio of the light absorbed at each wavelength to determine the peripheral oxygen saturation (SpO₂).

Option A: X-rays are a form of high-energy ionizing radiation used for imaging dense structures like bones and are not related to measuring oxygen saturation.
Option C: Ultrasonic waves are high-frequency sound waves, not light. They are used in sonography to create images of soft tissues and organs.
Option D: Gamma rays are a highly energetic form of electromagnetic radiation used in nuclear medicine (e.g., PET scans) and cancer therapy. They are not used for vital sign monitoring.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Principle of Pulse Oximetry as background academic context rather than a clinical decision trigger.
Pulse oximetry is a standard of care for monitoring oxygenation, considered the 'fifth vital sign' in many settings.
Nurses must be aware of factors that can cause inaccurate readings, such as dark nail polish, poor peripheral circulation, hypothermia, patient motion, and ambient light.
It is crucial to correlate the SpO₂ reading with the patient's overall clinical presentation. A patient can have a normal SpO₂ but still be in respiratory distress.

How to Approach the Question

First, identify the core concept of the question, which is the working principle of 'Pulse Oximetry'.
Recall that oximetry is a method to measure oxygen saturation. The '-metry' suffix implies measurement, and 'oxi-' relates to oxygen.
The key is how the device 'differentiates' between oxygenated and deoxygenated blood. This points to a specific physical property.
Remember that pulse oximetry is based on spectrophotometry, which involves light absorption.
Evaluate the options: X-rays, ultrasonic waves, and gamma rays are different forms of energy used for other diagnostic purposes (imaging bones, soft tissues, and nuclear medicine, respectively).
Select the option that involves light in the visible or near-visible spectrum, which is 'Infrared and Red light'.

Concept Tested & Keywords

Concept Tested: Principle of Pulse Oximetry
Stem keywords: Pulse Oximetry, oxygenated hemoglobin, deoxygenated hemoglobin, absorption
Lead-in keywords: based on
Negative lead-in flag: false

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