Pulse oximetry is a noninvasive technique that measures the peripheral arterial oxyhemoglobin saturation (SpO₂) of arterial blood. The reported result is a ratio, expressed as a percentage, between the actual oxygen content of the hemoglobin and the potential maximum oxygen-carrying capacity of the hemoglobin (Fischbach & Fischbach, 2018). A sensor, or probe, uses a beam of red and infrared light that travels through tissue and blood vessels. One part of the sensor emits the light, and another part receives the light. The oximeter then calculates the amount of light that has been absorbed by arterial blood. Oxygen saturation is determined by the amount of each light absorbed; nonoxygenated hemoglobin absorbs more red light and oxygenated hemoglobin absorbs more infrared light.

Sensors are available for use on a finger, a toe, a foot (infants), an earlobe, and forehead (Hess et al., 2021). It is important to use the appropriate sensor for the intended site and that it is fitted correctly (Hess et al., 2021); use of a sensor on a site other than what it is intended can result in inaccurate or unreliable readings. Circulation to the sensor site must be adequate to ensure accurate readings. Pulse oximeters also display a measured pulse rate.

It is important to know the patient's hemoglobin level before evaluating oxygen saturation because the test measures only the percentage of oxygen carried by the available hemoglobin. Thus, even a patient with a low hemoglobin level could appear to have a normal SpO₂ because most of that hemoglobin is saturated. However, the patient may not have enough oxygen to meet body needs (Morton & Fontaine, 2018).

A range of 90% to 100% is considered the normal SpO₂ (Bauldoff et al., 2020), depending on the patient's health status and health problems and needs; values ;90% are considered low (American Thoracic Society, 2021; MFMER, 2018b), indicate that oxygenation to the tissues may be inadequate, and should be investigated for potential hypoxia or technical error (Hinkle et al., 2022). When administering supplemental oxygen, most patients will have a target oxygen saturation of 94% to 98% (O'Driscoll et al., 2017). Patients with chronic obstructive pulmonary disease (COPD) and other risk factors for hypercapnia may have a target oxygen saturation of 88% to 92% (Mirza et al., 2018; Mitchell, 2015; O'Driscoll et al., 2017). Be aware of any prescribed interventions regarding acceptable ranges and/or check with the patient's health care team.

Pulse oximetry is useful for monitoring patients receiving oxygen therapy, titrating oxygen therapy, monitoring those at risk for hypoxia, monitoring those at risk of hypoventilation (opioids use, neurologic compromise), and postoperative patients. Pulse oximeter measurements are less accurate at SpO₂ less than 80%, but the clinical importance of this is questionable (Hess et al., 2021, p. 25). In addition, a patient's SpO₂ may remain relatively normal initially due to an increase in respiratory rate compensating for inadequate oxygen delivery (Dix, 2018; Elliott & Baird, 2019). Pulse oximetry does not replace arterial blood gas analysis. Desaturation (decreased level of SpO₂) indicates gas exchange abnormalities. Oxygen desaturation is considered a late sign of respiratory compromise in patients with reduced rate and depth of breathing.

Assessment

Assess for the presence of health problems that may impact oxygenation. Assess the patient's respiratory rate, rhythm, and depth and their mental status. Significant changes from baseline may indicate an alteration in oxygenation. Assess the patient's skin temperature and color, including the color of the nail beds. Temperature is a good indicator of blood flow. Warm skin indicates adequate circulation. Pallor (lack of color) of skin and mucous membranes can indicate less than optimal oxygenation. Cyanosis (bluish discoloration) and/or coolness or decreased temperature may indicate decreased blood flow or poor blood oxygenation. Check capillary refill; prolonged capillary refill indicates a reduction in blood flow. Assess the quality of the pulse proximal to the sensor application site. Assess for edema of the sensor site. Avoid placing a sensor on edematous tissue; the presence of edema can interfere with readings. Auscultate the lungs (see Skill 3-5). Note the amount of oxygen and delivery method if the patient is receiving supplemental oxygen.

Actual or Potential Health Problems and Needs

Many actual or potential health problems or issues may require the use of this skill as part of related interventions. An appropriate health problem or issue may include:

• Impaired gas exchange
• Ineffective airway clearance
• Activity intolerance

Outcome Identification and Planning

The expected outcomes to achieve when measuring oxygen saturation with a pulse oximeter is that the patient will exhibit oxygen saturation within their specified target range and based on their clinical status, and the heart rate displayed on the oximeter will correlate with the pulse measurement.

Implementation

Action	Rationale
1. Review the patient's health record for any health problems that would affect the patient's oxygenation status. Gather equipment.	Identifying influencing factors aids in interpretation of results. Assembling equipment provides for an organized approach to the task.
2. Perform hand hygiene and put on PPE, if indicated.	Hand hygiene and PPE prevent the spread of microorganisms. PPE is required based on transmission precautions.
3. Identify the patient.	Identifying the patient ensures the right patient receives the intervention and helps prevent errors.
4. Assemble equipment on the bedside stand or overbed table or other surface within reach.	Bringing everything to the bedside conserves time and energy. Arranging items nearby is convenient, saves time, and avoids unnecessary stretching and twisting of muscles on the part of the nurse.
5. Close the curtains around the bed and close the door to the room, if possible. Explain to the patient what you are going to do and why.	This ensures the patient's privacy. Explanation relieves anxiety and facilitates engagement with care.
6. Select an appropriate site for application of the sensor.	Inadequate circulation can interfere with the oxygen saturation (SpO2) reading.
a. Use the patient's index, middle, or ring finger (Figure 1).	Fingers are easily accessible.
b. Check the proximal pulse (Figure 2) and capillary refill (Figure 3) closest to the site.	Brisk capillary refill and a strong pulse indicate adequate circulation to the site.
c. If circulation to the site is inadequate, consider using the earlobe or forehead. Use the appropriate oximetry sensor for the chosen site.	These alternative sites are highly vascular. Correct use of appropriate equipment is vital for accurate results.
d. Use a toe only if lower extremity circulation is not compromised.	Peripheral vascular disease is common in lower extremities.
7. Select the proper equipment:
a. If one finger is too large for the probe, use a smaller finger.	Inaccurate readings can result if the probe or sensor is not attached correctly.
b. Use probes appropriate for the patient's age and size. Use a pediatric probe for a small adult, if necessary.	Probes come in adult, pediatric, and infant sizes.
c. Check if the patient is allergic to the adhesive. A nonadhesive finger clip or reflectance sensor is available.	A reaction may occur if the patient is allergic to an adhesive substance.
8. Prepare the monitoring site. Cleanse the selected area with a disposable cleansing cloth, as necessary; alternatively, have the patient wash their hands. Allow the area to dry. If necessary, remove any nail polish and artificial nails after checking the pulse oximeter's manufacturer's instructions.	Skin oils, dirt, or grime on the site can interfere with the passage of light waves. Research is conflicting regarding the effect of dark color nail polish and artificial nails. However, it is prudent to remove the nail polish (American Thoracic Society, 2021; USFDA, 2021; World Health Organization [WHO], 2011; Yönt et al., 2014). Refer to facility policy and the pulse oximeter's manufacturer's instructions regarding nail polish and artificial nails for additional information.
9. Attach the probe securely to the skin (Figure 4). Make sure that the light-emitting sensor and the light-receiving sensor are aligned opposite each other (not necessary to check if placed on the forehead).	Secure attachment and proper alignment promote satisfactory operation of the equipment and an accurate recording of the SpO2.
10. Connect the sensor probe to the pulse oximeter (Figure 5), turn the oximeter on, and check operation of the equipment (audible beep and fluctuation of the bar of light or waveform on the face of the oximeter).	An audible beep represents the arterial pulse, and a fluctuating waveform or light bar indicates the strength of the pulse. A weak signal will produce an inaccurate recording of the SpO2. The tone of the beep reflects the SpO2 reading. If SpO2 drops, the tone becomes lower in pitch.
11. Set alarms on the pulse oximeter. Check the manufacturer's alarm limits for high and low pulse rate settings (Figure 6).	The alarm provides an additional safeguard and signals when high or low limits have been surpassed.
12. Check oxygen saturation at regular intervals, as prescribed, as per nursing assessment, and as signaled by alarms. Monitor the hemoglobin level.	Monitoring SpO2 provides ongoing assessment of the patient's condition. A low hemoglobin level may be satisfactorily saturated yet inadequate to meet a patient's oxygen needs.
13. Remove the sensor on a regular basis and check for skin irritation or signs of pressure (every 2 hours for a spring-tension sensor and every 4 hours for an adhesive finger or toe sensor).	Prolonged pressure may lead to tissue necrosis. An adhesive sensor may cause skin irritation.
14. Clean nondisposable sensors according to the manufacturer's directions. Remove PPE, if used. Perform hand hygiene.	Cleaning equipment between each patient use reduces the spread of microorganisms. Proper removal of PPE reduces the risk for infection transmission and contamination of other items. Hand hygiene prevents the spread of microorganisms.

Evaluation

The expected outcomes have been met when the patient has exhibited an oxygen saturation within their specified target range and based on their clinical status, and the heart rate displayed on the oximeter has correlated with the pulse measurement.