Pulse oximetry: Clinical skills notes





Pulse Oximetry


As a nurse, you will help provide safe care to clients who have or are at risk for hypoxia, which is when there is not enough oxygen to meet the needs of the body. These clients require pulse oximetry, which is a non-invasive, easy, and pain-free method of measuring the amount of oxygen carried by the hemoglobin in the red blood cells. This is known as arterial blood oxygen saturation, or SaO2 for short. Maintaining a normal SaO2 ensures that the amount of oxygen that travels through the bloodstream to tissues around the body is adequate. 


A pulse oximeter consists of a probe, which is attached by a cable to a pulse oximeter. That probe has a light source on one side and a photodetector, or sensor, on the other side. So, when it gets clipped onto a body part, a light shines through the tissues on one side, and on the other side, the sensor detects how much light has been absorbed by the arterial blood in the tissues. The principle is that, when hemoglobin is bound to oxygen, it absorbs more light than when it’s not. 

Figure 1: Pulse oximeter.
There are several types of probes, depending on the site they can be placed.
  • Digit probes: fit onto a finger or toe; most common and easily used type
  • Earlobe probes: attach to the client's ear
  • Forehead probes: less commonly, if the digits or earlobes are inaccessible, a pulse oximetry probe can be applied across the forehead and secured with a headband
  • Sensor pads: can be used on several different sites, including an adult's earlobe or nose bridge and a newborn's palms or soles

Both earlobe and forehead probes tend to be more accurate than digit probes in cases when blood flow to the extremities is compromised or if the client moves their hands or feet frequently, creating motion artifacts.

All these probes can be either disposable, which are preferred when multiple clients need to be checked using the same oximeter, or reusable when used for a single client. They also come in two types: adhesive and clip sensors. In general, adhesive sensors are better for younger children or if you need to place the sensor on an earlobe, nose bridge, or toe. Clip sensors might not be the best for children because they are very easy to take off.

Figure 2: A. Digit probe, B. earlobe probe, C. forehead probe, D. sensor pads.

A pulse oximeter reading, also called SpO2, of 95% or greater is considered normal. Anything below that is considered low for most clients. But, if it falls below 85%, it can get really dangerous for the client. This may occur in clients with various lung conditions that interfere with gas exchange, meaning movement of oxygen and carbon dioxide between the blood, lungs, and tissues. 

In other cases, though, readings can be falsely low because of poor blood flow to the extremities, which makes it hard for the pulse oximeter to pick up a proper signal. This could be due to:
  • peripheral vascular disease, which happens when one of the arteries supplying the extremities becomes narrowed
  • hypotension, or low blood pressure
  • hypothermia, or decreased body temperature
  • several medications
  • peripheral edema, or accumulation of fluid and swelling of the limbs
  • smoke inhalation
  • carbon monoxide poisoning

Readings can also be inaccurate due to motion artifacts, like when the client is shivering or restless, meaning that false signals are generated when they shouldn’t be. Readings may also be inaccurate if the client is wearing nail polish, or if bright light, such as sunlight, is shining on the probe, making it harder to measure the oxygen saturation. 

  • Depending on the condition of the client, pulse oximetry can be used intermittently, meaning that you check the client’s SpO2 at certain times, or continuously, where the client is continuously connected to the pulse oximeter. In the latter case, an alarm can notify you if SpO2 falls below a certain level or if the probe falls off.
  • If the client is a child, remember that they will probably love to move, so it might be best to place the probe on their finger or toe; otherwise, you may get inaccurate readings. Also, avoid using forehead or nose probes with these clients.
  • Children, especially neonates, have delicate skin and can be easily injured, so remember to protect their skin, check under the probe regularly for skin breakdown, and routinely place the probe in a different spot.
  • In all cases, make sure to use the appropriate probe for those sites.
  • If the client is restless or moving too much, encourage them to stay still, try to assist them to hold their limb steady, or simply place the probe in a different spot.
  • Before clipping on a finger probe, check for the presence of nail polish or artificial fingernails and remove them.
  • In general, never place the probe on a thumb.
  • Don’t put the probe on the same limb as a blood pressure cuff; otherwise, the probe reading will be inaccurate whenever the cuff inflates.
  • To get the clearest reading, avoid exposure of the probe to direct bright light.
  1. Gather the supplies you’ll need, including the probe and the pulse oximeter.
  2. Check for any client factors that may affect the accuracy of the reading, which type and location of the probe should be used, if SpO2 needs to be measured continuously or intermittently, where to set the alarm limits, and how often you should check and record the SpO2.
  3. Perform hand hygiene.
  4. Place the probe; be sure to avoid placing it on skin that is not intact. If you’re using an adhesive sensor, make sure that the two sides of the probe are opposite each other.
  5. Plug the probe into the oximeter and turn it on.
  6. Listen for audible beeps and check the waveform on the oximeter screen. A good waveform will be consistent and regular and free of sudden jumps or flat lines.
  7. Check the client’s pulse to see if it matches the sound of the oximeter. If not, re-adjust the probe until it does.
  8. If SpO2 is measured continuously:
    • be sure that the alarm is on
    • check the integrity of the skin under the probe every two hours
    • move the probe to another spot every four hours
  9. For intermittent monitoring:
    • turn the oximeter off
    • remove the probe from the client
    • either clean it if it's reusable or discard it in the appropriate manner if it's disposable
    • perform hand hygiene

When caring for a client who is monitored with pulse oximetry, there are a few things you should report, such as an SpO2 below a value specific for the client, to the healthcare provider. 

Observe the skin integrity, color, moisture, and temperature at the site where the probe is placed. If there’s skin breakdown or irritation or the skin is pale, damp, or cold, choose another site for the probe. Check for any changes in vital signs or in the level of consciousness, unusual respiratory sounds, and bluish discoloration of the skin or mucous membrane.

  • the date and time
  • SpO2 reading
  • the observations you made while collecting the reading

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