All affect pulse oximeter reading, except?

NIMHANS Nursing Officer - 2021

Nursing Foundation

Medium

Appeared in: NIMHANS Nursing Officer - 2021

Explanation

Mild fever does not directly interfere with the spectrophotometric measurement used by a pulse oximeter.
The device measures the differential absorption of red and infrared light by oxygenated and deoxygenated hemoglobin; body temperature does not alter these properties.
While a high fever might be associated with shivering (motion artifact) or altered perfusion, a mild fever in itself is not a source of measurement error.

Option A: A bandage over the probe site can cause inaccurate readings by applying excessive pressure, which can diminish arterial pulsations or introduce venous pulsations. It can also physically block the light sensor.
Option C: Increased skin thickness, such as from calluses or edema, can impede the transmission of light from the oximeter's LED to the photodetector, resulting in a weak or absent signal.
Option D: Poor circulation (low perfusion) is a primary cause of inaccurate readings. The oximeter requires adequate pulsatile arterial blood flow to obtain a reliable signal. Conditions like hypotension, hypothermia, or peripheral vascular disease all lead to poor circulation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Factors affecting pulse oximetry accuracy as background academic context rather than a clinical decision trigger.
A nurse must always correlate the SpO2 reading with the patient's clinical presentation. An unexpectedly low reading in a patient who appears stable warrants troubleshooting the equipment and assessing for interfering factors.
Nursing interventions to improve a weak signal include warming the extremity, repositioning the probe to a different site (e.g., earlobe, forehead), removing nail polish, and ensuring the patient is still.
What if? If the patient had severe hypothermia instead of a mild fever, the pulse oximeter reading would likely be inaccurate. The cold would cause peripheral vasoconstriction, leading to poor circulation and a weak pulsatile signal, which is a known interference.

How to Approach the Question

First, identify the core of the question. It asks for the factor that does NOT affect pulse oximeter readings, which means it's an 'except' or negative-format question.
Your goal is to find the 'odd one out' from the options provided.
Evaluate each option based on your knowledge of how a pulse oximeter works. The device needs good pulsatile blood flow and unobstructed light transmission.
Consider Option A (Bandaging): This can physically obstruct light or circulation. It's a likely interference.
Consider Option C (Skin thickness): This can obstruct light. It's a likely interference.
Consider Option D (Poor circulation): This directly impacts the pulsatile signal. It's a very common interference.

Concept Tested & Keywords

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E6 Nursing Fundamentals Potter Perry 12e Part 3 p. 24-26

E6 Nursing Vital Signs p. 66-68