Which of the following CANNOT cause a false pulse oximetry reading in a patient with respiratory distress?

AIIMS BBSR SNO - 2019

Fundamental of Nursing

Medium

Appeared in: AIIMS BBSR SNO - 2019

Explanation

Hyperthermia, or elevated body temperature, does not negatively interfere with pulse oximetry readings.
It typically causes peripheral vasodilation (widening of blood vessels), which can improve blood flow and the pulsatile signal, potentially making the reading more reliable.
Nursing literature identifies hypothermia (low temperature) as a cause of inaccuracy due to vasoconstriction, but not hyperthermia.

Option A: This is a primary cause of false readings. Pulse oximeters require adequate pulsatile arterial blood flow to differentiate between arterial and venous blood. Conditions like hypotension, shock, or peripheral vascular disease reduce this flow, leading to unreliable or unobtainable readings.
Option B: This is a known cause of false readings. Oedema (swelling) in the extremity where the probe is placed can increase the distance between the probe's light emitter and detector and scatter the light, obscuring the arterial pulsation and leading to inaccurate measurements.
Option D: This is a well-documented cause of false readings. Dark-colored nail polish (e.g., black, blue, brown) and artificial nails can absorb the specific wavelengths of light used by the oximeter, which interferes with the device's ability to calculate oxygen saturation, often resulting in a falsely low reading.

Clinical Relevance

Nursing practice connection: Knowing Factors affecting pulse oximetry accuracy helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses must always perform a quick assessment for factors that can interfere with SpO2 readings to avoid making clinical decisions based on inaccurate data.
If a pulse oximetry reading is unexpectedly low or does not align with the patient's clinical presentation, the nurse's first action should be to troubleshoot. This includes checking for a warm extremity, removing nail polish, ensuring proper probe placement, and trying an alternative site (like an earlobe or forehead).
What if? If the patient had severe hypothermia instead of hyperthermia, the SpO2 reading would likely be inaccurate or unobtainable due to intense peripheral vasoconstriction. The nursing priority would be active rewarming and using a more central monitoring site for oxygen saturation.

How to Approach the Question

First, identify the negative keyword "CANNOT". This signals that you are looking for the one option that is an exception.
The question requires you to find the factor that does NOT cause a false pulse oximetry reading. This means three of the options are known causes of interference.
Recall the basic principle of pulse oximetry: it measures light absorption through pulsatile arterial blood in a capillary bed.
Evaluate each option's effect on this principle:
Inadequate circulation: Weakens the arterial pulsation, causing a bad signal. This interferes.
Oedema: Scatters light and can compress vessels, weakening the signal. This interferes.

Concept Tested & Keywords

Concept Tested: Factors affecting pulse oximetry accuracy
Stem keywords: pulse oximetry, false reading, respiratory distress
Lead-in keywords: CANNOT
Negative lead-in flag: The question asks for the factor that does NOT cause a false reading, which is a negative framing.

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