Consult the manufacturer’s instructions for the designated site placement of the sensor.
Do not attach the sensor to a finger, earlobe, or the bridge of the nose if the area is edematous or if skin integrity is compromised. Do not attach the sensor to fingers that are hypothermic.
Conditions that decrease arterial blood flow, such as peripheral vascular disease, hypothermia, hypotension, and peripheral edema, affect the accuracy of oxygen saturation readings. Pharmacologic vasoconstrictors also decrease arterial blood flow.
Pulse oximeters overestimate oxygen saturation in patients with acute respiratory failure, chronic bronchitis, and emphysema; however, monitoring trends is helpful. If a pulse oximeter reading is questionable, obtain arterial blood gas (ABG) values to determine oxygen saturation.undefined#ref1">1,5
Pulse oximetry is the noninvasive measurement of peripheral oxygen saturation (SpO2), which is expressed as the percentage of hemoglobin that is filled with oxygen. A pulse oximeter has a sensor with a light-emitting diode (LED) connected by a cable to an oximeter or contained in a one-piece portable battery-operated device. The LED emits light wavelengths that are absorbed differently by oxygenated and deoxygenated hemoglobin molecules. The more hemoglobin that is bound to oxygen, the higher the oxygen saturation.4 In general, the normal range for SpO2 is 95% to 99%.2 A consistent SpO2 of less than 95% should be investigated, and an SpO2 of 90% signifies developing hypoxemia.2 Pulse oximetry devices have a margin of error of 3% to 4%, especially in critically ill patients and newborns.3
Pulse oximetry is indicated for patients who are hypoxemic or who are at risk for impaired gas exchange. The measurement of SpO2 is simple and painless and has few of the risks associated with more invasive measurements of oxygen saturation (e.g., ABG sampling). Taking measurements with a digit or earlobe sensor requires a vascular, pulsatile area to detect the change in the sensor’s transmitted light. Conditions that decrease arterial blood flow (e.g., peripheral vascular disease, hypothermia, peripheral edema) affect accurate determination of oxygen saturation in these areas. For patients with decreased peripheral perfusion, a forehead reflectance sensor should be applied.
Factors that affect light transmission (e.g., outside light sources, patient motion) also affect the measurement of SpO2. Direct sunlight or fluorescent lighting should be avoided when using an oximeter, or the sensor should be protected with an opaque covering or towel. The sensors in most devices used in the home are contained in a light-blocking cover. Carbon monoxide in the blood, jaundice, and intravascular dyes can influence the light reflected from hemoglobin molecules. Levels of SpO2 measured in these conditions may be inaccurate. If factors affect light transmission, oxygenation levels should be obtained through ABG sampling instead.4
In adults, reusable and disposable oximeter sensors, if available, can be applied to the earlobe, finger, toe, bridge of the nose, or forehead. Each sensor is designated for a different part of the body. The sensors are not interchangeable, so a sensor for the finger (Figure 1) or toe should not be used on the ear or nose.
Some limitations may impact the accuracy of pulse oximeters, such as poor circulation; dark skin pigmentation; thick skin; current use of nicotine-containing products; cool skin; dark fingernail polish; and long, artificial nails. The pulse oximeter reading should not be used alone to determine the state of health.2
See Supplies tab at the top of the page.
Do not place a reusable clip-on finger sensor on the thumb; it is not designed for the thumb.
Rationale: Peripheral vasoconstriction alters SpO2.
Do not attach the sensor to fingers or toes that are hypothermic.
Rationale: The site must have adequate local circulation and be free of moisture.
Rationale: If the patient has obesity, a clip-on sensor may not fit properly.
Place the sensor on its designated site only; otherwise, an erroneous reading may be obtained.
Do not use a clip-on digit sensor on the patient’s thumb.
Rationale: Opaque coatings decrease light transmission; nail polish containing blue pigment absorbs light emissions and alters the SpO2 measurement.
Rationale: Correct hand positioning ensures sensor position and decreases motion artifact that interferes with SpO2 determination.
Rationale: Normal breathing prevents large fluctuations in minute ventilation and possible changes in SpO2.
Rationale: The pulse waveform display and audible beep are proportional to the pulse and SpO2 value. Manually obtaining the pulse rate confirms oximeter accuracy.
National Health Service (NHS). (2022). Guidelines on oxygen and oximetry. Retrieved June 23, 2023, from https://handbook.ggcmedicines.org.uk/guidelines/respiratory-system/guidelines-on-oxygen-and-oximetry/
Siegel, B.K., Heuer, A.J., Kallet, R.H. (2021). Chapter 19: Analysis and monitoring of gas exchange. In R.M. Kacmarek, J.K. Stoller, A.J. Heuer (Eds.), Egan’s fundamentals of respiratory care (12th ed., 368-394). St. Louis: Elsevier.
*In these skills, a “classic” reference is a widely cited, standard work of established excellence that significantly affects current practice and may also represent the foundational research for practice.
Clinical Review: Suzanne M. Casey, MSN-Ed, RN
Published: August 2023
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